Dissertations / Theses on the topic 'Volcanoes – Indonesia'

This thesis set out to investigate the influence of disturbance on the succession of the Krakatau islands (Rakata, Sertung, Panjang). The hierarchical model of succession by S. Pickett and colleagues (1987) was adopted as a research framework, and provided the basis for an alternative model of succession on Krakatau that focuses on processes rather than successional pathways. Investigations were conducted on (i) the meso-scale, and (ii) the patch-scale, (i) quantified the recent disturbance regime, and inter- and intra-island differences in diversity, (ii) compared sapling performance (growth, mortality and recruitment), and species compositional patterning in space and time for saplings and the seed bank with respect to island, gap size and severity of disturbance. Multivariate techniques were used, and amongst other attempts at characterising the light environment, hemispherical photography was employed. For the first time the effect of a continuous period of volcanic activity (1992-1995) of Anak Krakatau could be directly quantified and compared between Panjang and Sertung (ash-affected) and Rakata (receiving no ash). Increased rates of gap formation in the volcanically active period in comparison to the previous decade were found for all islands. This supports the disturbance-driven model of Whittaker and colleagues. However, an extension is required, because, contrary to expectation, Rakata also experienced more disturbance. This increase is argued to be a result of more severe weather conditions, and an increased number of earth tremors, during times of volcanic activity. The disturbance factors of extreme climatic events (e.g. ENSO events) and human impact are also proposed for inclusion in the alternative model. Drought associated with the 1994 El Niño is of relevance to short-term and potential long-term impact on regeneration dynamics and succession. Attention was drawn to the local human influence of pumice mining on the coastal forests. Supporting previous findings on the plot- and whole island scales, data from species presence/absence transects established that species richness and beta-diversity on the ash- affected islands was also lower on the meso-scale. Panjang's canopy composition is less uniform, and locally more species-rich than Sertung's. More evidence of the suggested decline of the mono-dominant species Neonauclea calycina and Timonius compressicaulis was gathered. The third dominant, Dysoxylum gaudichaudianum, is expanding in the lowlands of all islands. This is aided by its ability to regenerate in moderate shade, to grow rapidly in gap environments, and its tolerance of ash-fall, drought and herbivory. However, on Rakata, it is not expected to become generally mono-dominant because a considerable number of other potential canopy species are present. Sapling performance and species composition and its changes were in general strongly affected by ash-fall and drought. These factors tended to override effects of gap size and severity of disturbance. Advance regeneration, and the composition of the local forest type were identified as important factors influencing the composition of the early stages of gap-fill. The local forest type also seemed to contribute most to seed bank composition. As rarer species tended to have clumped distributions, and 'safe sites' for regeneration seemed not to be limiting, dispersal constraints were argued to be the most likely factors slowing diversification, unless further severe volcanic disturbance leads to successional set-back. The latter also strongly limits the predictability of succession on Krakatau.

Volcanic and magmatic processes are controlled by the composition of the magmas involved and the nature and structure of their underlying plumbing systems. To understand and predict volcanic behaviour, it is of critical importance to characterize the associated magmatic plumbing and supply system. This study investigates the magma plumbing system beneath Bali, Indonesia by employing several thermobarometric models using mineral phases in lavas from the simultaneous eruptions of Agung and Batur volcanoes in 1963 and the 1974 eruption of Batur. Compositional data were acquired from feldspar, pyroxene, and olivine crystals, using electron microprobe analysis, as well as from whole-rock samples using inductively coupled plasma mass spectrometry. Clinopyroxene-melt and clinopyroxene composition thermobarometers were then applied to equilibrated clinopyroxene-melt couples, while plagioclase-melt thermobarometry was employed on equilibrated plagioclase-melt pairs. The results were used to construct comprehensive magmatic plumbing models for Agung and Batur and are compared with geochemical, geophysical and petrological data on these volcanoes and others in the region. For the 1963 Agung eruption, results from clinopyroxene-melt thermobarometry suggest dominant crystallisation levels between 18 and 22 km depth. Clinopyroxene from the 1963 eruption of Batur record crystallisation depths between 12 and 18 km, whereas clinopyroxene from the 1974 Batur eruption show a main crystallisation level between 15 and 19 km. Furthermore, plagioclase-melt thermobarometry indicates the existence of shallow level magma reservoirs, with depths between 3 and 7 km for the 1963 eruption of Agung, between 2 and 4 km for the 1963 Batur eruption and between 3 and 5 km for the 1974 Batur event. The deep magma storage regions notably coincide with lithological boundaries in the crust and mantle beneath Bali, while the shallow reservoirs are consistent with recent geophysical studies that point to regional shallow-level magma storage. An along-arc comparison reveals this trend to be characteristic of Sunda arc magma storage systems and highlights the utility of a thermobarometric approach to detect multi-level systems beneath recently active volcanic systems.

Dans l'histoire des éruptions volcaniques, le Papandayan à l'Ouest de Java est considéré comme l'un des plus meurtriers après avoir causé la mort de 2957 personnes et des dégâts sérieux en 1772. L'éruption la plus récente de ce volcan a eu lieu en 2002 et était de type phréatique. Cette éruption a été précédée d'une augmentation soudaine de l'activité sismique moins de deux jours avant l'éruption. Aucune victime n'a été déplorée. La nature de cette éruption est indéfinie. Cette thèse regroupe plusieurs études utilisant différentes techniques en vue d'améliorer la prédictibilité des éruptions du volcan Papandayan, principalement via l'interprétation des signatures sismiques.

Le monitoring sismique passif a débuté en décembre 2009 par l'installation d'une station sismique permanente à large bande dans le cratère du Papandayan. L'année suivante, une station météorologique a été installée pour compléter les mesures. La troisième année, 8 stations sismiques temporaires ont été déployées autour du volcan en réponse à une augmentation de l'activité sismique en 2011.

Nous avons conduit différentes études; (1) Nous avons examiné l'évolution de l'activité volcanique par réalisation d'une revue complète de l'histoire éruptive du volcan, autant pour la période préhistorique qu'historique. (2) Nous avons réalisé une analyse temps-fréquence des événements sismiques, étudié leurs caractéristiques et proposé une nouvelle classification avec une description des processus physiques supposés les générer. (3) Nous avons étudié les signatures sismiques précurseur de l'éruption de 2002 et pendant la crise volcanique de 2011 en implémentant différentes méthodologies, dont: la détection automatique d'événements sismiques à l'aide de filtres récursifs STA/LTA, l'analyse spectrale des formes d'onde, la mesure continue de l'amplitude spectrale du signal (SSAM), la polarisation des ondes et l'analyse de la distribution fréquence/magnitude (b-value). Nous avons alors réalisé un modèle chronologique des séquences sismiques du Papandayan. (4) Pour améliorer la compréhension de la dynamique des fluides sous le volcan Papandayan, nous avons réalisé une analyse des fréquences complexes des événements longue période (LP) et leurs variations temporelles peuvent être utilisées pour estimer (a) la composition des fluides présents dans les fractures sous le volcan et/ou (b) l'évolution des dimensions de ces fractures. Ces variations des fréquences complexes des événements LP peuvent être interprétées comme les réponses dynamiques du système hydrothermal à des changements d'impulsions de chaleur transférées par les flux de gaz volcaniques du magma sous le volcan. (5) nous avons calculé l'évolution temporelle du rapport spectral horizontal-sur-vertical (HVSR) en utilisant le bruit sismique ambiant enregistré par une station unique pour estimer les variations de vitesse de propagation des ondes de cisaillement en lien avec l'activité dynamique du volcan. Nous avons trouvé une corrélation claire entre les variations de fréquence de résonnance HVSR et l'augmentation de la sismicité.

Enfin, nous proposons des hypothèses sur les processus physiques qui se produisent sous le Papandayan. Cette étude est une première tentative d'utilisation de cette méthode pour surveiller l'activité volcanique en continu.

Doctorat en Sciences
info:eu-repo/semantics/nonPublished

Kawah Ijen (2386 m) is a stratovolcano located within Ijen Caldera, at the easternmost

part of Java island in Indonesia. Since 2010, the volcano has been equipped with seismometers

and several sensors (temperature and level) have been immersed in its acidic lake waters and in the acidic river seeping on the volcano flanks. While finding instruments capable of resisting to such extreme conditions (pH~0) has been challenging, the coupling of lake monitoring techniques with seismic data improves the knowledge of the volcanic-hydrothermal dynamics. Moreover, the monitoring capabilities have been considerably

enhanced supporting the decision-making of the authorities in case of emergency.

Several methods and processing techniques were used to analyze the seismic data. Much effort has been given to implement the seismic velocities (Moving Window Cross Spectral Analysis (MWCSA)) calculations. At Kawah Ijen, the frequency band that is less affected by the volcanic tremor and the seasonal fluctuations at the source ranges between 0.5-1.0 Hz. Moreover, a stack of 5 days for the current CCF gives reliable results with low errors and allows to detect fluctuations which are missed using a 10-day stack.

The background seismic activity mostly consists in low frequency events and a continuous tremor of low amplitude. Fluctuations of the lake temperature and level result from the recharge of the hydrothermal system during the rainy season. Kawah Ijen lake waters are not perfectly mixed and a shallow stratification occurs during the rainy season, because meteoric waters are less dense than the lake fluids.

Different unrest occurred during our study. Some of them strongly affected the volcanic lake, while others did only weakly. In the first category, a strong unrest commenced in October 2011 with heightened VT (Volcano Tectonic) earthquakes and low frequency events activity, which culminated mid-December 2011. This unrest was correlated with an enhanced heat and hydrothermal fluids discharge to the crater and significant variations of the relative velocities (~1%). This suggests an important build-up of stress into the system. VT earthquakes opened pathways for the fluids to ascend, by increasing the permeability of the system, which latter allowed the initiation of monochromatic tremor (MT) when the steam/gases interacted with the shallow portions of the aquifer. Our calculations evidence a higher contribution of steam in March 2012 that might explain the increase of the MT frequency when bubbles were observed at the lake surface. This period was also characterized by short-lived but strong velocity variations, related to water level

rises containing important amount of bubbles, and important heat and mass discharges

into the lake. On the contrary, the second category of unrest did only slightly affect the

lake system. This could be explained by a dryer hydrothermal system and/or locations of

the seismic sources, which were not directly linked to the lake.

While a magmatic eruption will likely be preceded by a strong seismic activity, the major challenges remain to understand why the unrest we studied did not lead to an eruption and to identify precursory signs of a phreatic eruption. Even a small phreatic eruption would be devastating for the people working everyday in the crater and the ones

who live nearby the voluminous acidic lake.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

La caldera du volcan Rinjani contient un lac d’un volume de 1 km³ qui est probablement le plus grand lac volcanique au monde présentant une anomalie thermique nette. Ce lac présente une composition neutre chlorure sulfate bicarbonate inhabituelle pour les lacs volcaniques. Sa TDS (2600 mg/l) et conductivité (3500µs/cm) élevées indiquent un apport de fluides hydrothermaux très important. Enfin, son alcalinité élevée (520 mg/l), indique un apport important de dioxyde de carbone dans le lac.

Les sources thermales situées autour du Gunung Baru (cône volcanique situé dans la caldera) ont une composition chimique en éléments majeurs et une composition isotopique proche de celles du lac volcanique indiquant qu’elles sont essentiellement le résultat du recyclage du lac par le système hydrothermal. Les variations de compositions entre les différentes sources ont permis de montrer que leurs compositions est le résultat du mélange entre un fluide hydrothermal profond de composition neutre chlorure, dont la température a été estimée à 270°C, et d’un fluide plus superficiel riche en magnésium et en sulfate.

Le flux de dioxyde de carbone à la surface du lac a été estimé à l’aide de la méthode de la chambre d’accumulation et par calcul à environ 2300 t/j, ce qui représente un apport significatif de gaz. Cependant, comme le lac présente une structure polymictique, le risque d’accumulation de dioxyde de carbone en profondeur et donc d’éruption limnique peut être exclus.

Pour la première fois dans cette thèse, le modèle d’estimation des flux thermiques émis par les lacs volcaniques mis au point par Stevenson (1992) a été contraint par des mesures des paramètres météorologiques mesurés en continu, ce qui a permis de valider le modèle. De plus, nous avons pu montrer que l’essentiel des variations de températures des lacs volcaniques est dû à des variations météorologiques. En utilisant le flux thermique plutôt que la température, il est dès lors possible d’avoir accès à des variations de l’activité volcanique.

Le flux thermique estimé pour le lac du Rinjani est de 1700 MW, ce qui représente le flux le plus élevé jamais mesuré sur un lac volcanique aérien. Ce flux thermique est aussi plus élevé que le flux thermique mesuré sur des lacs de lave à 800°C. Ce paradoxe apparent s’explique par la plus grande dimension des lacs volcaniques, la capacité calorifique de l’eau quatre fois plus importante que celle du magma et la viscosité de l’eau 1 million de fois inférieure, ce qui fait de l’eau un excellent fluide caloporteur pour transporter les calories vers la surface.

Doctorat en Sciences
info:eu-repo/semantics/nonPublished

L’intérêt de la télédétection appliquée aux volcans actifs et potentiellement dangereux a été démontré depuis longtemps dans la mesure où cette technique a participé à l’amélioration de la compréhension des processus éruptifs et des aléas volcaniques, amélioration qui permet une réduction des risques volcaniques. Nous avons entrepris plusieurs études volcanologiques reposant sur l’usage d’images de moyenne et haute résolution spatiale, qu’elles soient optiques (IKONOS, Pléiades, GeoEye, Quickbird and SPOT5), radar (ALOS-PALSAR) ou bien thermiques (ASTER et MODIS «hot spot»). Associées à l’analyse de MNTs et de photographies aériennes acquises par un drone, ces études ont consisté à appliquer des techniques de télédétection sur le Semeru et le Merapi, deux des volcans composites les plus actifs et les plus densément peuplés de l’ile de Java en Indonésie. Cette recherche fondée sur la télédétection a permis de mettre en évidence des structures géologiques et tectoniques, d’identifier, de classer et de cartographier des dépôts éruptifs sur les deux volcans et a servi à améliorer l’évaluation des risques à la suite des grandes éruptions de 2002-2003 au Semeru et de 2010 au Merapi. Nous avons également initié une étude afin de comprendre les interactions entre l’activité éruptive et le contexte sismo-tectonique régional en utilisant l’analyse des données MODIS avec la méthode MODVOLC. Nous avons remis à jour la carte géologique du volcan Semeru en y associant des données issues de l’interprétation d’images HSR récentes, des photographies aériennes, l’analyse de MNTs et des observations de terrain, notamment dans le réseau hydrograhique qui convoie des lahars. Nous avons décrit l’histoire éruptive postérieure à 2001 au Semeru en incluant la grande éruption à l’origine des écoulements pyroclastiques (EPs) en 2002-2003 et les éruptions effusives de 2012-2014, qui constituent un phénomène rarement observé sur ce volcan. Le Semeru a produit un volume de 2.5 ± 0.5 106m3 de coulées de lave provenant du cratère sommital entre 2010 et 2014, ce qui peut annoncer, pour la première fois depuis 1967 ou 1941, une modification profonde du style éruptif de ce volcan. Au moment de terminer cette thèse, le dome-coulée situé dans le cratère Jonggring-Seloko continue à croître et les coulées de lave dépassent 2 km de longueur dans la cicatrice majeure en pente raide sur le flanc SE ; leurs fronts pourraient s’effondrer et produire des EPs dont le volume moyen pourrait excéder les valeurs de 3 à 6.5 million de m3 mesurées sur la période 1967-2007. Les écoulements futurs pourront déborder des parois de la cicatrice vers l’aval et se propager vers les vallées des flancs est et sud-ouest. L’épisode éruptif du 26 octobre au 23 novembre 2010 s’est avéré l’événement majeur de l’activité du Merapi depuis 1872. Notre interprétation des images HSR démontre qu’à l’issue des éruptions explosives, le sommet du Merapi a perdu un volume de 10 x 106m3 et la gorge de Gendol orientée SSE a été élargie jusqu’à mesurer 1.3 x 0.3 x 0.2 km. Le nouveau cratère élargi et profond inclut le dome post-2010, qui a été fracturé en 2013, tandis que ses parois verticales instables peuvent être fragilisées par les explosions mineures de 2013 et 2014. Nous avons identifié et cartographié les dépôts pyroclastiques et de lahar de 2010 en appliquant plusieurs méthodes de classification aux images optiques HSR et aux données polarisées de Radar à Synthèse d’Ouverture (RSO). Les résultats démontrent la capacité de l’imagerie satellitaire HSR à capturer l’extension et les impacts de dépôts immédiatement après une grande éruption et avant tout remaniement. Cette technique met en exergue l’utilité de l’imagerie haute résolution et des données radar pour les volcans en activité persistante dont l’accès est souvent rendu impossible. (...)
Remote sensing has long been recognized as a tool for analysis at active and hazardous volcanoes because it can augment our understanding of the processes that underlie volcanic activity so as enable us to apply this understanding to volcanic risk reduction. This thesis presents a volcanological study using High-Spatial Resolution optical images (IKONOS, Pléiades, GeoEye, Quickbird and SPOT5 satellites), radar data (ALOS-PALSAR sensor) and thermal (ASTER satellite and MODIS hot spot) images. In association with DEMs and low-altitude aerial photographs, remote sensing techniques have been applied for tracing the evolution of activity at Semeru and Merapi, two of the most active and densely populated volcanoes in Java, Indonesia. This remotely sensing-based study has unraveled structures, geological features and erupted deposits of both volcanoes and has improved the existing hazard assessment after their most recent eruptions. The thesis also presents the first advance towards deciphering possible interactions between regional tectonic earthquakes and renewed stages of eruptive activity of Merapi and Semeru volcanoes based on the analysis of volcanic hotspots detected by the MODVOLC technique. The geological map of Semeru is updated, including additional data derived from the interpretation of the most recent satellite images, aerial photographs, DEM analysis and fieldwork. The post-2001 eruptive activity at Semeru, including the large PDC-forming eruption in 2002-2003 and uncommon lava flow eruptions in 2010-2014 are investigated. The fact that Semeru has produced several lava flows from the central summit vent between 2010 and 2014 may herald a profound change in eruption style for the first time since at least 1967. At the time of writing, a dome-fed coulée in the Jonggring-Seloko crater continues to grow and lava flows are extending to distances of >2 km down Semeru's SE-scar; their fronts may collapse and produce large-volume pyroclastic density currents (PDCs), perhaps exceeding the average (1967-2007) volume range of 3 to 6.5 million m3. Future dome-collapse PDCs may travel farther down the main SE scar and can spill over its lowermost rims towards the southwest and eastward radiating drainage network. The 26 October-23 November 2010 eruption was the Merapi’s largest event since 1872 (it attained VEI=4). The interpretation of HSR images shows that due to the explosive eruptions, the summit area lost about 10 x 106m3 and the SSE-trending Gendol Breach enlarged to reach 1.3 x 0.3 x 0.2 km in size. The new, enlarged and deep summit crater including the 2010 lava dome is extremely unstable having been weakened by the post-2010 explosive events. This instability is a result of the steep Gendol Breach below the mouth of the crater and the steep and unstable crater walls. The 2010 Merapi pyroclastic and lahar deposits have been identified by applying several classification methods to HSR optical images and dual-polarization synthetic aperture radar (SAR) data. The results show the ability of remotely sensed data to capture the extent and impacts of pristine deposits shortly after emplacement and before any reworking, and highlight the purpose of using high-spatial resolution imagery and SAR data on persistently active volcanoes where access for field survey is often impossible. The 2010 tephra and PDC deposits covered ca. 26 km2 in two catchments of Gendol and Opak Rivers on Merapi’s south flank, i.e. 60-75% of the total PDC deposit area and a total bulk volume of 45 x 106m3. The tephra-fall deposit covered an area of ca. 1300 km2 with a volume range of 18-21 x 106m3. Volumes of these deposits were estimated using the areas determined from remote sensing data and deposit thickness measured in the field. (...)
Penginderaan jauh telah lama dikenal sebagai suatu alat untuk analisis di gunungapi aktif dan berbahaya karena dapat meningkatkan pemahaman kita tentang proses yang mendasari aktivitas gunung berapi sehingga memungkinkan kita untuk menerapkan pemahaman ini dalam pengurangan risiko erupsi gunungapi. Disertasi ini menyajikan studi vulkanologi menggunakan citra satelit optik resolusi tinggi (IKONOS, Pléiades, GeoEye, Quickbird dan SPOT5), data radar (ALOS-PALSAR sensor) dan citra termal (satelit ASTER dan hotspot MODIS). Dalam kaitannya dengan DEM dan foto udara, teknik penginderaan jauh telah diterapkan untuk melihat evolusi aktivitas di Semeru dan Merapi, dua gunung berapi yang paling aktif dengan kepadatan penduduk yang tinggi terletak di Pulau Jawa, Indonesia. Studi berbasis penginderaan jauh ini telah mengkaji struktur, fitur geologi dan material erupsi dari kedua gunungapi tersebut dan telah mempertajam penilaian bahaya yang ada setelah erupsi terkini. Disertasi ini juga menyajikan kemajuan awal dalam menafsirkan kemungkinan interaksi antara gempa tektonik regional dan aktivitas gunungapi Merapi dan Semeru berdasarkan analisis hotspot vulkanik yang terdeteksi oleh MODVOLC. Peta geologi Semeru telah diperbaharui dengan memasukkan data tambahan yang berasal dari interpretasi citra satelit terbaru, foto udara, analisis DEM dan data lapangan. Aktivitas erupsi pasca-2001 di Semeru, termasuk erupsi dengan aliran pirokastik (Pyroclastic Density Current/PDC) besar pada tahun 2002-2003 dan erupsi tidak biasa dengan aliran lava pada 2010-2014, telah dikaji. Fakta bahwa Semeru telah menghasilkan beberapa aliran lava dari kawah di puncak antara tahun 2010 dan 2014, mengindikasikan perubahan besar dalam gaya erupsi untuk pertama kalinya setidaknya sejak 1967. Pada saat penulisan disertasi ini, sebuah kubah lava (Coulée) di kawah Jonggring- Seloko terus tumbuj dan aliran lava yang memanjang hingga jarak >2 km arah tenggara Semeru; ujung lava kemungkinan dapat runtuh dan menghasilkan aliran piroklastik yang mungkin melebihi volume rata-rata (tahun 1967 hingga 2007) dalam kisaran 3-6.5 juta m3. Aliran piroklastik yang akan datang mungkin mengalir sepanjang gawir utama ke arah tenggara dan dapat menyebar melampaui lereng paling bawah ke arah barat daya dan ke arah timur menyebar ke jaringan drainase. Erupsi yang terjadi pada 26 Oktober-23 November 2010 adalah erupsi terbesar Merapi (mencapai VEI 4) sejak 1872. Interpretasi citra resolusi tinggi menunjukkan bahwa daerah puncak kehilangan batuannya sekitar 10 juta m3 akibat erupsi eksplosif. Erupsi juga memperbesar “Gendol Breach” dengan orientasi tenggara menjadi berukuran 1.3x0.3x0.2 km. Kawah puncak yang baru, diperbesar dan dalam, termasuk juga kubah lava tahun 2010 sangat tidak stabil dan telah diperlemah oleh beberapa erupsi eksplosif pasca-2010. Ketidakstabilan ini diakibatkan oleh curamnya Gendol Breach di bawah mulut kawah dan kondisi dinding kawah yang curam dan tidak stabil. Deposit piroklastik dan lahar diidentifikasi dengan menerapkan beberapa metode klasifikasi terhadap citra optik resolusi tinggi dan data dual-polarisasi Synthetic Aperture Radar (SAR). Hasilnya menunjukkan kemampuan data penginderaan jauh untuk merekam jangkauan dan dampak dari deposit murni sesaat setelah pengendapan dan sebelum proses erosi, serta menyoroti tujuan penggunaan citra resolusi tinggi dan data SAR di gunungapi sangat aktif dengan akses untuk survei lapangan sering kali tidak memungkinkan. Endapan tephra dan PDC menutupi area sekitar 26 km2 di dua DAS, Kali Gendol dan Opak, di sisi selatan Merapi, atau 60-75% dari total luas endapan PDC, dan total volume 45 juta m3. Deposit tephra jatuh menutupi area seluas sekitar 1.300 km2 dengan volume 18-21 juta m3. Volume endapan vulkanik ini diestimasi menggunakan informasi luas yang ditentukan dari data penginderaan jauh dan ketebalan yang diukur di lapangan. (...)

Soputan volcano is one of the few basaltic volcanoes among 127 active volcanoes in Indonesia. It is part of the Sempu-Soputan volcanic complex located south of Tondano Caldera, North Sulawesi and commonly produces both explosive eruptions with VEI 2-3 and effusive lava dome and flow eruptions. Over the last two decades, Soputan had thirteen eruptions, the most recent in 2016. Most eruptions started explosively, followed by dome growth and in some cases pyroclastic flows. Our study focuses on understanding the magmatic system of Soputan and what processes are responsible for its highly explosive eruptions, which are typically uncommon for a basaltic magma composition. Our study includes tephra samples predating the 1911 eruptions, lava flow samples from the 2015 eruption, and ash from a 2015 fallout deposit. Our whole rock major and trace element composition are virtually identical to lava flow and select pyroclastic deposit compositions of Kushendratno et al. (2012) for the 1911-1912 and 1991-2007 eruptions. Bulk rocks contain 49 to 51 wt.% SiO2, whereas 2015 ash samples are slightly more silicic with 53 wt.% SiO2, consistent with segregation of groundmass from phenocrysts in the eruption cloud. Mantle normalized incompatible trace elements indicate strongly depleted HFSE (High Field Strength Elements) and REE (Rare Earth Elements) signatures but with spikes at Pb and Sr and mild enrichment of Rb and Ba. In comparison of data of this study with what was reported by Kushendratno et al. (2012), Fo68-79 olivine-hosted melt inclusions range from basaltic (48-52 wt.% SiO2) to basaltic andesite (54-55 wt.%) as compared to 54 - 65 wt.% SiO2 glass in Fo68-74 olivines. The compositional range of melt inclusions is consistent with 50% fractionation of multiple minerals including observed phenocrysts of olivine, plagioclase, pyroxene and oxides. Compositional trends with an inflection point likely reflect a change in the crystallizing assemblage, where early crystallization includes clinopyroxene and plagioclase, while later crystallization is dominated by plagioclase. New volatile concentration data from melt inclusions (S max. 0.35 wt.%, Cl max. 0.17%, H2O max. 5.2 wt.% from FTIR analyses) are higher than previously reported from younger samples (S max. ~0.07 wt.%, Cl max. 0.2%, H2O max. ~1 wt.%). H2O is relatively constant (~1-4 wt.%) for individual tephra samples (data by FTIR and water by difference method). Our inclusion data suggest that more volatile-rich magmas exist at depth and this is consistent with a model whereby recharge of deep, volatile-rich magmas into a more degassed and crystal-rich magma initiates a new, highly explosive eruption.

Surface manifestations of hydrothermal fluids such as fumaroles and hot springs provide valuable information about the level of activity of a volcano during quiescent period. Geochemical study of gas and spring waters is useful to elaborate geochemical model for magmatic-hydrothermal system. Furthermore, temporal geochemical monitoring of these fluids with time provides a better understanding in processes occurring inside the volcano and can be useful to detect any changes in the activity of the magmatic-hydrothermal system. This thesis investigates two hydrothermal systems at Kelud and Papandayan volcanoes that are located at Java Island in Indonesia. Kelud is considered as one of the most dangerous volcanoes of Java because of its frequent eruptions. After the last eruption that occurred in 1990, a new lake rapidly filled the crater of Kelud volcano. Water samples collected since 1993 are near neutral Na-K chloride fluids and are typical of aged hydrothermal system where the acidity has been completely neutralized by fluid-rock interaction and where the emission of acid magmatic gases has stopped. Two sudden increases in lake temperature in 1996 and 2001 were accompanied by rapid changes in lake water compositions and suggest the existence of two hydrothermal systems feeding the lake: a shallow hydrothermal system dominated by Ca-Mg sulfate waters and a deepest aquifer with neutral alkali chloride waters. From 2001 to 2005, measurements of CO2 emitted by the surface of the lake were performed by using the accumulation chamber method modified in order to work at the surface of a crater lake. Two statistical methods were used to process data: the graphical statistical and stochastic simulation methods. The results of graphical statistical approach showed that two different degassing processes are acting at the lake surface: one corresponding to CO2 fluxes resulting from rising bubbles and the other corresponding to equilibrium diffusion of dissolved CO2 at the water-air surface. Total CO2 emission rate estimated by stochastic simulation ranges from 105 t/day for 2001 to 32 t/day for 2005. Thermal energy released by the lake was also estimated by using an energy balance model with a new constraint using the CO2 flux. The thermal flux decreased from 200 MW (2001) to 100 MW (2002) and then remained stable. Correlation between the chemical data of waters, the fluxes of CO2 and energy show that a constant decrease in the level of activity of the volcano since 1993 occurred although the lake temperature has been stable since 2003. Since the last magmatic eruption that occurred in 1772, phreatic eruptions occur on Papandayan volcano with the last one in 2002. The volcanic material ejected during this eruption is essentially made of altered rocks from within the hydrothermal system. The interaction of acid waters with the host rocks corresponds to an advanced argilic alteration. The chemical compositions of waters from Papandayan volcano and Kelud lake waters are contrasting. Indeed, the spring waters sampled since 1994 are acid sulfate-chloride waters and acid sulfate waters. The chemical and isotopic analyses of gases and waters suggest a significant magmatic contribution in SO2, HCl and HF to the hydrothermal system. The chemical composition of waters sampled after the 2002 eruption have provided information about origin of this eruption. Decrease in chloride concentration and in delta 34S of dissolved sulfates showed that the magmatic contribution in these fluids are less important and that the waters are likely to be formed by the condensation of steam (H2O, H2S) rising from a boiling aquifer.

Doctorat en sciences, Spécialisation géologie
info:eu-repo/semantics/nonPublished

The largest naturally-occurring lake of hyperacid brine in the world is located in the crater of Kawah Ijen volcano in East Java, Indonesia. The hyperacid Banyu Pahit River flows down the side of Kawah Ijen and is a major source of regional natural pollution. Hydrothermal fluid, meteoric derived groundwater, seepage from the hyperacid crater lake, and water-rock interaction are the major sources and sinks of water and solutes from the volcano to the surrounding environment. The current research is focused on the upper Banyu Pahit River valley (within 3 km of the summit) which has been understudied to date. Detailed chemical analyses of the Banyu Pahit River, the crater lake, and all observed springs (neutral and acid) that contribute water to the river were made, including 46 major, minor and trace elements. The distinct chemical signature of each water source, as well as that of water-rock interaction, is determined. Several elements have been identified as conservative tracers of hydrologic sources and sinks as they enter the surface water system. Mass balance mixing analysis using the conservative tracers, combined with discharge measurements, is used to quantify the fluid and solute mass contribution of each source. The results of this analysis indicate that fluid from the deep hydrothermal system contributes the majority of the solute flux from Kawah Ijen, and that it also forms the headwaters of the Banyu Pahit River. The flux of crater lake seepage, which was previously assumed to be both the main source of acid water for the Kawah Ijen hydrologic system and the headwaters of the Banyu Pahit River, has now been determined to be a full order of magnitude lower than that of hydrothermal fluid (total calculated flux = 1.2 l/s crater lake seepage versus 15.4 l/s hydrothermal fluid).
Le plus grand lac naturel de saumure hyperacide du monde est situé dans le cratère du volcan Kawah Ijen, dans la province de Java Est, en Indonésie. La rivière hyperacide Banyu Pahit s'écoule sur le flan du Kawah Ijen et constitue une importante source de pollution naturelle régionale. Les fluides hydrothermaux, l'eau souterraine d'origine météorique, les eaux d'exfiltration provenant du lac du cratère et les interactions eau-roche représentent les principaux puits et sources d'eau et de solutés de ce basin. La présente étude est centrée sur la vallée du cours supérieur de la rivière Banyu Pahit (dans un rayon de 3 km du sommet), une région sur laquelle peu d'études se sont penché. Des analyses chimiques détaillées (incluant 46 éléments majeurs, mineurs et en traces) ont été effectuées sur les eaux de la rivière Banyu Pahit, du lac du cratère et de toutes les sources observées (neutres et acides) qui contribuent à l'écoulement de la rivière. La signature chimique distincte de toutes les sources d'eau, ainsi que celle des interactions eau-roche, a été établie. Plusieurs éléments s'avèrent être des traceurs conservatifs de sources et puits hydrologiques du système d'écoulement de surface. L'analyse de mélange basée sur le bilan massique des traceurs conservatifs, combinée aux mesures de débit d'écoulement, est utilisée pour quantifier la contribution massique de fluides et solutés de chaque source. Les résultats de cette analyse indiquent que les fluides provenant du système hydrothermal profond sont responsables de la majeure partie de l'apport de solutés provenant du Kawah Ijen et qu'ils constituent également la source de la rivière Banyu Pahit. Il est maintenant établi que l'apport du lac aux eaux de surface du basin, apport qui jusqu'à present était considéré comme dominant, est largement inférieur à l'apport associé aux fluides hydrothermaux (débit calculé total = 1,2 l/s pour l'apport du lac cont

Improving our understanding of magma plumbing and storage remains one of the majorchallenges for petrologists and volcanologists today. This is especially true for explosivevolcanoes, where constraints on magma plumbing are essential for predicting dynamicchanges in future activity and thus for hazard mitigation. This study aims to investigate themagma plumbing system at Anak Krakatau; the post-collapse cone situated on the rim of the1883 Krakatau caldera. Since 1927, Anak Krakatau has been highly active, growing at a rateof ~8 cm/week. The methods employed are a.) clinopyroxene-melt thermo-barometry (Putirkaet al., 2003; Putirka, 2008), b.) plagioclase-melt thermo-barometry (Putirka, 2005), c.)clinopyroxene composition barometry (Nimis & and Ulmer, 1998; Nimis, 1999; Putirka,2008) and d.) olivine-melt thermometry (Putirka et al., 2007). Previously, both seismic(Harjono et al., 1989) and petrological studies (Camus et al., 1987; Mandeville et al., 1996a;Gardner et al., in review, J. Petrol.) have addressed the magma plumbing beneath AnakKrakatau. Interestingly, petrological studies indicate shallow magma storage in the region of2-8 km, while the seismic evidence points towards a mid-crustal and a deep storage, at 9 and22 km respectively.This study shows that clinopyroxene presently crystallizes in a mid-crustal storage region(8-12 km), a previously identified depth level for magma storage, using seismic methods(Harjono et al., 1989). Plagioclases, in turn, form at shallower depths (4-6 km), in concertwith previous petrological studies (Camus et al., 1987; Mandeville et al., 1996a; Gardner etal., in review, J. Petrol.). Pre-1981 clinopyroxenes record deeper levels of storage (8-22 km),indicating that there may have been an overall shallowing of the plumbing system over thelast ~40 years. The magma storage regions detected coincide with major lithologicalboundaries in the crust, implying that magma ascent and storage at Anak Krakatau is probablycontrolled by crustal discontinuities and/or density contrasts. Therefore, this study shows thatpetrology has the sensitivity to detect magma bodies in the crust where seismic surveys faildue to limited resolution. Combined geophysical and petrological surveys offer an increasedpotential for the thorough characterization of magma plumbing at active volcanic complexes.

Les connaissances actuelles sur le comportement hydrogéologique des édifices volcano-détritique sont encore limitées et cela limite la bonne gestion des ressources en eau. Depuis une décennie, sur les flancs du volcan Merapi, à Java Centre, en Indonésie, une pression croissante se fait sur la ressource en eau avec l'intensification des pratiques agricoles irriguées, la croissance de la population et les utilisations industrielles de l'eau. Le manque de connaissances sur les processus du cycle de l'eau par les consommateurs déclenche des conflits d'usage et le partage de l'eau devient une question centrale. Une compréhension plus précise du cycle de l'eau dans sa globalité dans ce genre de contexte est donc un point fondamental qui a besoin d'être amélioré.Ce travail a été axé sur la caractérisation des ressources en eaux souterraines à travers l’étude de la géométrie et des propriétés hydrodynamiques des systèmes aquifères /aquitards multi-couches à l'échelle d’un bassin versant expérimental sur le flanc Est du volcan Merapi. Pour couvrir tous les processus impliqués dans la circulation des eaux souterraines, une approche multi-disciplinaire a été choisi.Une nouvelle approche géologique et géomorphologique a été réalisé afin de caractériser la structure interne et l'architecture de dépôt sur le flanc Est du Merapi. Sur la base de ces résultats, un modèle conceptuel géologique et géomorphologique a été construit et révèle des formations détritiques chenalisées et connectées depuis les hautes altitudes jusqu’aux vallées, créant des chemins préférentiels pour les eaux souterraines.La caractérisation du climat avec l'estimation des termes du bilan hydrique et la description des principaux processus hydrologiques sont décrits par le suivi de deux années hydrologiques (2011-2012 et 2012-2013 ). Le climat tropical de cette région se caractérise par une période de mousson (Novembre à Mai ) et une saison sèche (Juin à Octobre ). Le bilan hydrologique est caractérisé par 40 % des précipitations sont perdus par évapotranspiration, 10 % s'écoulent et la moitié restante s'infiltre à travers l'édifice volcano-détritique et recharge les aquifères multicouches.Le fonctionnement hydrogéologique d'un environnement volcano-détritique complexe a pu être appréhendé à l’aide d’un suivi hydrogéologique, hydrochimique et géochimiques sur les sources et des puits peu profonds. Deux ceintures de sources ont été identifiées: la première est caractérisée par des sources de dépression alignées le long d'une ligne topographique tandis qu'une faille normale est probablement à l'origine de la seconde. L’utilisation de la température de l’eau de source comme traceur de l’altitude de recharge a permis l’identification de plusieurs systèmes aquifères multi-couches. Les propriétés hydrauliques de ces aquifères ont été établi à partir des l'analyses des essais hydrauliques. Le premier système aquifère est situé proche de la surface et possède une faible conductivité hydraulique. En revanche, un second système aquifère a été identifié en profondeur et possède une forte perméabilité. Le traceur “température” met en évidence un effet de mélange entre le premier et le deuxième aquifère au niveau des sources de basses altitudes . Ce phénomène est confirmé par les résultats des analyses isotopiques.L'application d'un modèle numérique couplant la circulation des flux, le transfert de masse ou le transfert de chaleur confirme le modèle conceptuel hydrogéologique et permet de quantifier la ressource en eau
The current knowledge on the hydrogeological behavior of the volcano-detritic edifices is still sparse and these lacks limit the attempting of water resource management. Since a decade, on the flanks of Merapi volcano, in Central Java, Indonesia, an increasing pressure is done on the water resource with the intensification of the irrigated agriculture practices, the growth of population and the water industrial uses. The lack of knowledge about the water cycle processes by the consumers triggers water use conflicts and the water sharing becomes a central issue. A most accurate understanding of the water cycle in its globality in this kind of context is hence a fundamental point that need to be improved.This work has been focused on the characterization of groundwater resource thought the identification of the extent, the geometry and hydrodynamic properties of the aquifers/aquitards multi-layered system at the experimental catchment scale on the Eastern flank of Merapi volcano. To cover all the processes involved into the groundwater circulation, a multi-disciplinary approach has been chosen.A new geological and geomorphological approach is performed to characterize the internal structure and the deposit architecture on this zone of the Eastern flank of the Merapi. Based on these results, a geological and geomorphological conceptual model has been built and insists on the channelized detritic formations connected from the upper parts to the low lands through the volcanic edifice and that create preferential groundwater path ways.The climate characterization with the estimation of the water balance terms and the description of main hydrological processes are described with the monitoring of two hydrological years (2011-2012 and 2012- 2013). The tropical climate of this region is characterized by seasonal monsoon (November to May) and dry season (June to October). The global water balance can be distributed as follow: 40% of rainfall are lost by evapotranspiration, 10% runs off and the remaining half infiltrates through the volcano-detritic edifice to recharge the multi-layered aquifers.The hydrogeological functioning of a complex volcano-detritic environment is explained through the implementation of hydrogeological, hydrochemical and geochemical monitoring on inventoried springs and wells. Two spring belts are described, the first one is characterized by depression spring along a topographic line while a normal fault is probably at the origin of the second one. The identification of a multi-layered aquifer systems has been done based on the determination of the spring water temperature as a relevant tracers of the recharge elevation and the groundwater circulations. The hydraulic properties of these aquifers have been investigated from the analysis of hydraulic tests. Results show a low permeable aquifer close to the surface with a local recharge while a second aquifer system with high permeability and regional recharge is located deeper. The tracer temperature shows a mixing effect between the first and the second aquifers in the springs at low elevation. This phenomenon is confirmed by the isotope analysis.The application of a coupled numerical model between flow circulation, first mass transfer and second heat transfer confirms the hydrogeological conceptual model of volcano-sedimentary edifice and allows to quantify the water resource

This research develops a conceptual model of trust during emergency evacuations in Indonesia. Drawing upon the cultural theory of Douglas (1978) as the theoretical basis, this research explores and identifies the main components required to build a conceptual model in agent-based modelling and simulation (ABMS) by: (1) improving the existing situational judgment test (SJT) scoring method for clustering people's trust into cultural categories; (2) identifying the differences between each cultural category; and (3) investigating the factors that encourage people in each category to shift to another category when they face three different situations. To accomplish the research goal, a two-case comparative study in Merapi and Sinabung is conducted using: (1) semi-structured interviews with government representatives, non-government leaders, and anthropologists; and (2) an empirical survey of villagers in Merapi and Sinabung. The interview results are analysed using thematic analysis, which provides the information needed to develop the initial conceptual model and to construct the SJT used in the survey questionnaire. The survey results are then analysed using three different methods: (1) hierarchical and k-means clustering, to improve the existing SJT scoring method; (2) a non-parametric test to identify the differences between cultural categories; and (3) multinomial logistic regression (MLR) to identify the factors encouraging people in each category to shift to another category. Finally, the survey results are used to verify the initial conceptual model developed following the interviews. The research finds that the hierarchical and k-means clustering methods can successfully improve the existing SJT scoring method due to the higher consistency achieved in the validation process. Four and two cultural categories are found in Merapi and Sinabung, respectively. On the other hand, this research also successfully distinguishes between the cultural categories based on attributes grouped into three aspects - socio-demographic, evacuation behaviour, and psychological aspects - and identifies the factors that encourage people in each category to shift to another category when they face three different situations: (1) when the volcano shows eruption signs; (2) when a long duration eruption occurs; and (3) when the volcano erupts. These results are used as the main components to verify the initial conceptual model of trust. The verified conceptual model developed in this research can be utilised in the future as a basis on which to simulate people's trust during emergency evacuations using ABMS, and can also help policy-makers in Indonesian disaster management to better comprehend future ABMS.

Porphyry and high sulfidation epithermal ore-forming systems are genetically associated with calc-alkaline volcanism in subduction zones, and where erosion has not been too deep, the volcanic rocks are still commonly exposed in close proximity to the deposits. Most models for porphyry copper and high sulfidation epithermal gold systems include a shallow magmatic reservoir (the porphyry stock), an overlying hydrothermal cell, its alteration paragenesis and a stratovolcano. Some investigations also discuss the importance of underlying granitoid batholiths as feeders for porphyry stocks and their hydrothermal systems. Although it is commonly believed that the ores deposit during the waning stages of volcanism, given the time span over which these deposits form (tens of thousands to several million years) and the undeniable existence of hydrothermal systems beneath volcanoes, it is quite probable that their formation is initiated at times when volcanoes are still active. Although currently mined ore deposits are excellent places to focus research, subduction zone stratovolcanoes provide important windows on the magmatic-hydrothermal processes at play.This thesis describes an investigation of the magmatic-hydrothermal environment that resides beneath Merapi volcano, Indonesia. The research involved sampling and chemical analysis of minuscule aliquots of evolving silicate and sulfide melts trapped as inclusions at different times and in different locations in growing crystals subsequently ejected during eruptions. The research also involved sampling and analysis of fumarolic gases (and their precipitates) emitted at Merapi volcano during times of quiescence and eruptive activity, as well as compilation of published compositional data for fumarolic gases from other arc volcanoes. These gases are the surface equivalents of ore-forming magmatic-hydrothermal fluids. Finally the research involved compilation from the literature of compositional data for fluid inclusions (micron-scale droplets of magmatic volatile phases) trapped in gangue minerals in porphyry copper deposits. The focus of the research was the behaviour of copper, nickel, cobalt, zinc, lead and molybdenum in magmatic hydrothermal systems.The research reported in Chapter 1 showed that injections of sulfide melt-saturated mafic magma into shallower, more evolved and more oxidized resident magma at Merapi volcano induced exsolution of a magmatic volatile phase from the mafic magma. This hydrothermal fluid dissolved the sulfide melt and became enriched in chalcophile (notably copper) and siderophile metals. An argument is presented that the overpressure generated by the exsolution of a fluid originating in this manner triggered an explosive eruption at Merapi volcano in 2006. This is supported by the observation that the metal content, particularly of copper, was higher in the volcanic gas sampled immediately after this eruption than during periods of quiescence and that metal ratios of the gas are remarkably similar to those of sulfide melt inclusions. In Chapter 2, it is shown that the mafic magma mixed poorly with the more felsic magma, that both magmas evolved via assimilation and fractional crystallization and, most importantly, that the magmatic volatile phase transferred base metals to the more felsic magma. In Chapter 3, the fluid inclusion and volcanic gas data are used to make inferences about the evolution of porphyry ore-forming systems and link mechanisms of ore-formation to those operative during the eruptive cycles of volcanoes. Finally, the thesis integrates the findings of this study into a model that provides new insights into the formation of porphyry copper deposits below stratovolcanoes.
Les gîtes de types porphyriques et épithermaux sont génétiquement associés au volcanisme des zones de subduction et les roches volcaniques cogénétiques à ces gisements sont souvent encore présentes. Tous les modèles actuels de mise en place de ces gîtes définissent un réservoir magmatique peu profond, lequel est coiffé d'une cellule hydrothermale et de sa séquence complexe d'altération, ainsi que d'un stratovolcan. Certains auteurs discutent aussi de l'importance de batholites sous-jacents ayant généré le porphyre et ses fluides hydrothermaux. Quoiqu'il soit généralement accepté que ces gîtes se forment durant le déclin du volcanisme, étant donné la longévité des périodes proposées pour la formation de ceux-ci (de dizaines de milliers à plusieurs millions d'années) et l'existence indéniable de systèmes hydrothermaux associés, il est fort probable que la formation de ces gîtes soit initiée alors que le volcanisme est encore actif. Les volcans situés en zones de subduction représentent d'importants points d'observation des processus magmatiques-hydrothermaux actuels.La présente recherche porte sur l'environnement magmatique-hydrothermal qui existe sous le volcan Mérapi, situé en Indonésie. Des échantillons de liquides silicatés et sulfurés piégés à l'intérieur de cristaux durant leur croissance à différents moments et endroits dans le magma et avant d'être éjectés hors des réservoirs magmatiques lors d'éruptions volcaniques ont été prélevés et dosés. Des gaz fumerolliens de haute température et leurs sublimats émis au volcan Mérapi durant des phases de dégazage passif et d'éruption explosive ont été échantillonnés et analysés. Des résultats similaires pour les gaz d'autres volcans, ainsi que des analyses d'inclusions fluides de systèmes hydrothermaux de porphyres cuprifères ont été compilés à partir de la littérature. Les gaz volcaniques analysés sont les équivalents superficiels des fluides magmatiques-hydrothermaux qui génèrent les gisements métallifères.Dans le premier chapitre, il a été démontré que des magmas mafiques d'origine profonde et saturés en liquide sulfuré ont été injectés dans le réservoir magmatique peu profond de Mérapi, celui-ci contenant un magma plus évolué et plus oxydé. La décompression qu'a subie le magma mafique a provoqué l'exsolution d'une phase magmatique volatile (un fluide hydrothermal) qui a dissous le liquide sulfuré et ses métaux chalcophiles et sidérophiles (notamment le cuivre). La surpression générée par l'exsolution de ce fluide hydrothermal a provoqué l'éruption explosive du volcan Mérapi de mars à août 2006. Ceci est corroboré par l'observation que certains métaux, particulièrement le cuivre, étaient enrichis dans les gaz volcaniques émis après l'explosion par rapport aux niveaux mesurés durant la phase de dégazage passif, et par le fait que les rapports des métaux dans ces gaz post-explosion étaient soudainement semblables à ceux mesurés dans les inclusions sulfurées, alors qu'ils étaient bien différents durant les phases de dégazage passif du volcan. Dans le second chapitre, je démontre que le magma plus mafique et le magma plus felsique ne se sont pas bien mélangés, que les deux magmas ont évolué via l'assimilation de roches encaissantes et la cristallisation fractionnée, et que la phase magmatique volatile qui s'est séparée du magma mafique et qui a dissous le liquide sulfuré a transféré ses métaux au magma plus felsique. Dans le troisième et dernier chapitre, les inclusions fluides et les gaz volcaniques ont été utilisés en conjonction avec les connaissances acquises et décrites dans les deux premiers chapitres afin de proposer un modèle pour l'évolution du système porphyrique et d'établir les liens qui existent entre les mécanismes de formation des gîtes porphyriques et épithermaux acides, et ceux qui opèrent durant les cycles éruptifs des volcans. Un modèle pour la formation des porphyres cuprifères sous les stratovolcans actifs des zones de subduction est finalement proposé.

Les volcans sont des espaces qui combinent aléas et ressources naturelles, cette dernière justifiant la forte densité de population vivant sur de nombreux volcans actifs en milieu tropical. Au-delà d’une source de matériaux de construction, certains volcans sont considérés comme de véritables châteaux d’eau, offrant d’importantes possibilités d’adduction d’eau potable au travers de systèmes aquifères complexes et parfois artésiens. Le système aquifère du volcan Bromo-Tengger à l’Est de l’Ile de Java en Indonésie représente une ressource stratégique grâce à sa principale source artésienne Umbulan qui alimente en partie la deuxième plus grande ville d’Indonésie (Surabaya). Depuis plus d’une décennie, cette ressource subit une pression croissante avec une augmentation des besoins en eau pour les pratiques agricoles, le développement industriel, l’augmentation de la population et est accentuée par des techniques de forage de plus en plus accessibles. Connu comme l’un des stratovolcans les plus visités au monde, le potentiel aquifère du Bromo-Tengger n’était jusqu’ici que très peu étudié.Dans le cadre de ce travail, une approche multidisciplinaire a été utilisée pour caractériser l’hydrogéologie du flanc Nord du Bromo-Tengger et sa plaine artésienne.Les résultats géologiques et géophysiques ont permis de préciser la lithologie et la géométrie des formations aquifères du volcan mais également d’identifier le contexte d’émergence des exutoires naturels telles que les grandes sources artésiennes de piedmonts volcaniques.Les conditions climatiques ont été caractérisées avec la mise en place de stations météorologiques le long du flanc Nord du volcan et complétées par l’instrumentation d’un bassin versant représentatif. Confrontées aux données hydrochimiques et isotopiques, elles ont permis une analyse quantitative de la distribution de la recharge et l’élaboration d’un premier modèle conceptuel hydrogéologique. La recharge s’effectue sur tout le flanc du volcan (≈66% de la pluie) avec une zone préférentielle de recharge identifiée vers 1000 m d’altitude due principalement aux effets orographiques. Conceptuellement, les eaux infiltrées alimentent un système binaire composé d’un réseau d’aquifères perchés alimentant tout ou partie un aquifère libre de base dont la partie terminale devient captive vers la plaine au travers d’un aquifère artésien multicouche, expliquant les fortes productivités aquifères de la zone.Un nouveau dispositif de mesure sur forages artésiens a été développé, combinant essai par pompage et mesure du charge hydraulique. Leur interprétation permet d’estimer les paramètres hydrodynamiques ainsi que la réalisation une carte piézométrique de l’aquifère artésien de Pasuruan. Ces derniers résultats, ont permis de définir les principales directions et systèmes d’écoulement ainsi que les temps de transit.Un premier modèle numérique d’écoulement en régime permanent montre une bonne cohérence avec le modèle conceptuel précédemment développé. Il permet une meilleure compréhension du fonctionnement hydrogéologique dans la situation présente et celle de pré-exploitation. Confronté aux données d’analyse d’âge de l’eau souterraine dans la plaine, il permet de discuter du modèle d’écoulement le plus réaliste à considérer à l’échelle du volcan.Ces travaux de recherche contribuent à améliorer la connaissance hydrogéologique des stratovolcans andésitiques en position d’arc volcanique sous climat tropical, incluant une caldera, des aquifères perchés de haute altitude ainsi qu’une plaine volcano-sédimentaire multicouche et artésienne
AbstractVolcanoes are environments combining hazards and natural resources, the latter justifying the high population density living on many active volcanoes in tropical contexts. More than a source of construction materials, some volcanoes are considered as "water castles", providing important possibilities for drinking groundwater supply through complex and sometimes artesian aquifer systems. The Bromo-Tengger volcano aquifer system in East Java, Indonesia, is a strategic resource with its main artesian spring Umbulan, which partly supplies the second biggest city of Indonesia (Surabaya). For more than a decade, this resource has been under increasing pressure with an increase of water abstraction for agricultural practices, industrial development, population growth and is amplified by increasingly accessible drilling techniques. Known as one of the most visited stratovolcanoes in worldwide, the aquifer potential of the Bromo-Tengger was barely studied until now.As part of this thesis, a multidisciplinary approach was used to characterize the hydrogeology of the northern flank of the volcano and its downstream artesian plain. Geological and geophysical results have highlighted the lithology and the geometry of the volcano's aquifer formations. The outflow context of natural major artesian springs of volcanic piedmonts area such as Umbulan has been identified.The climatic conditions were characterized with the installation of new meteorological stations along the northern flank and completed by the monitoring of a representative watershed. Compared with hydrochemical and isotopic data, they allowed a quantitative analysis of the distribution of the recharge and the elaboration of a first hydrogeological conceptual model. The recharge covers the whole northern flank of the volcano (≈66% of the rain) with a preferential recharge zone identified at about 1000 m elevation mainly due to orographic effects. Conceptually, infiltrated waters supply a binary system composed of: a network of high elevation perched aquifers feeding all or part of a low-lying basal aquifer. This latter becomes confined towards the plain through a multi-layer artesian aquifer, explaining the high aquifer productivity of the area.A new measurement device at free-flowing artesian well has been developed, combining hydraulic tests and piezometric measurement. Their interpretation allows both estimating the hydrodynamic parameters and drawing a piezometric map of the artesian aquifer of Pasuruan. These last results, made it possible to define the main flow directions and systems as well as an estimate of groundwater transit time.A first steady-state numerical flow model shows good consistency with the conceptual model previously developed. It allows a better understanding of the hydrogeological functioning in the present and pre-exploitation conditions. Compared with the water age dating analyses, it allows to discuss the most realistic flow model to consider at the scale of the volcano.This research provides new insights in the understanding of hydrogeology of andesitic stratovolcanoes in volcanic arc position under tropical climate including a caldera, high-elevation perched aquifers with a multi-layered and artesian volcano-sedimentary plain.Keywords: Hydrogeology, Bromo-Tengger volcano, conceptual hydrogeolgoical model of volcanic aquifer, volcano-sedimentary plain, artesianism, recharge, multidisciplinary

Adam Bobbette Cultures of Forecasting: Volatile and Vulnerable Nature, Knowledge, and the Future of Uncertainty Summary This dissertation is a cultural history and ethnography of volatile nature forecasting. It looks at the ways that the future of nature is known in highly unpredictable contexts through a broad history of modernist nature forecasting and an ethnography of state scientists, shamans, and a sultans retinue on the active volcano, Mount Merapi, Indonesia. The project aims to understand how practices of forecasting generate futures, mobilize, and organise anticipation, how time is known, and populations governed. It looks at the way that publics emerge through forecasting technologies, and how futures and nature-culture relations are contested. It follows the practices of scientists in volcano and tsunami observatories, in planes tracking tropical storms, and bunkers dug into active volcanoes; at how instruments and technologies such as seismographs, windows, globes, speakers, and electrical tomography, mediate and transform relations with nature, the future, and governance. It considers too, the role of architecture, shamanism, and the state in appropriating and governing uncertainty. By following the fieldwork of geophysicists and volcanologists in observatories and the edge of the caldera of Mount Merapi, as well as spirit possession practices, and the ritual offerings of a sultan, I demonstrate how practices of forecasting are making contested futures lived in the present, and forging infrastructures and tools for their longevity. Forecasting, I demonstrate, is a cultural technique that negotiates the porous borders between the human, nature, and the future.

The psychosocial well-being of survivors of armed conflicts, forced displacement, and/or natural disasters is becoming more and more an integral component of holistic humanitarian response. Yet many organisations rely on broad, generalised manuals or guidelines which do not take into account the unique characteristics of societies and target populations. This paper describes the author’s research with disaster survivors in Java, Indonesia, and refugee in Sweden, aiming to characterise the process of recovery, adaptation and integration through beneficiaries’ own words. The author looks at how theory can be applied, such as whether a hierarchy of needs can be universally relevant, how the host Swedish society affects refugees’ experiences, which so-called “states of being” subjects experience, and how religion and cultural differences like individualism and collectivism influence one’s ability to regain psychosocial well-being. The author used both in-depth interviews and quantitative questionnaires to obtain data. Results showed an incredible level of resilience and positivity among all groups, though Indonesians reported family, spirituality and the community as major helping factors, while many refugees in Sweden pointed to their own individual determination and will to succeed. Many Indonesians identified economic livelihood as the biggest remaining gap, while refugees in Sweden spoke of language skills, educational qualifications and employment as keys to success and integration. Many challenges and gaps remain, especially for newly arrived refugees facing an increasingly difficult job market and fewer opportunities.

High-sulfidation epithermal deposits are genetically associated with calc-alkaline volcanism in subduction zones, and although these ore deposits are excellent places to focus research, subduction zone stratovolcanoes provide important windows on magmatic-hydrothermal processes that are not available from study of the corresponding ore deposits. There is general agreement that the hydrothermal alteration accompanying the high-sulfidation epithermal ores is the product of volcanic degassing, however, there is considerably less agreement on the nature and origin of the ore fluid. Opinion is divided over whether the ore fluid is a vapor or a liquid, and whether it is entirely volcanic or of mixed volcanic-meteoric origin.The research presented here details a field-based investigation of the magmatic-hydrothermal environment of Kawah Ijen volcano, an active stratovolcano (mainly andesitic pyroclastics and lavas) located in the Ijen Caldera Complex in Java, Indonesia. The Kawah Ijen crater is approximately one kilometer in diameter and contains a hyperacidic lake (pH ~ -0.5) and a small and actively degassing solfatara, which is surrounded by a much larger area of acid-sulfate alteration that was exposed during a phreato-magmatic eruption of the volcano in 1817; the eruption excavated the crater to a depth of 250 m. The research described in this thesis involved sampling and chemical analyses of the gases and their condensates (the surface equivalents of the ore-forming magmatic-hydrothermal fluids) collected from the solfatara and rock samples taken from the alteration center.Condensed fumarolic gases (pH ~ -0.5) released from the solfatara and sampled at temperatures between 330 and 495 °C contain up to 3 ppm Cu and 3.8 ppm As; the concentration of Ag is below detection. The alteration center is characterized by zones of residual silica, alunite-pyrite and kaolinite/dickite; based on alunite-pyrite geothermometry, the area formed at a temperature between 200 and 300 °C. High sulfidation epithermal mineralization occurs in this area in the form of massive and vein-hosted pyrite that contains up to 200 ppb Au, 9 ppm Ag, 6,800 ppm Cu, and 3,430 ppm As; these elements are invisible at the highest resolution of scanning electron microscopy, and thus occur either in the form of nano-particles or are in solid solution in the pyrite.The manuscript in Chapter 3 summarizes the observations detailed above to support a model in which highly acidic gases condensed ~ 250 m beneath the floor of the pre-1817 crater at Kawah Ijen volcano. In the area near the source of the vapors, the ratio of fluid to rock was extremely high and resulted in the leaching of elements from the andesitic host rock, leaving behind a residue of "vuggy silica." With increasing distance from the source, in an area of intermediate fluid/rock ratio, the condensed liquids replaced the primary minerals of the host with alunite and pyrite. The kaolinite/dickite zone formed in a rock-buffered environment (low fluid/rock ratio), in the zone furthest from the vapor source. Gold- silver- and copper-bearing phases were undersaturated in the condensed liquids, however, they were able to concentrate by adsorbing on the surfaces of the growing pyrite crystals, which developed p-type conductive properties as a result of the uptake of arsenic. The metals were incorporated in the pyrite either by their electrochemical reduction to form native metal nano-particles, through coupled substitutions with arsenic for iron and sulfur, or in the case of Cu, by direct replacement of Fe. This thesis provides new insight into the formation of high-sulfidation epithermal deposits, showing, in particular, that high sulfidation epithermal precious metal mineralization can form directly from condensed volcanic gases and that the processes of alteration and metallic mineralization occur synchronously.
Les dépôts épithermaux à forte sulfuration sont génétiquement associés au volcanisme calco-alkalin dans les zones de subduction, et bien que ces gisements métallifères soient intéressants pour la recherche, les stratovolcans des zones de subduction fournissent un bon aperçu quant aux procédés magmatiques et hydrothermaux, absent dans l'étude seule de ces gisements. Il existe un accord global sur le fait que le dégazage volcanique soit responsable de l'altération hydrothermale accompagnant les minerais épithermaux à forte sulfuration. Cependant l'avis est considérablement moins unanime sur la nature et l'origine des fluides du minerai. Le fluide minéralisateur pourrait être soit vapeur ou liquide, et son origine pourrait être soit entièrement volcanique ou soit un mélange volcanique-météorique. Cette étude présente les détails d'une étude sur l'environnement magmatique-hydrothermal du volcan Kawah Ijen, un stratovolcan actif (produisant principalement des pyroclastites andésitiques ainsi que des laves) situé dans le Complexe Ijen Caldera à Java en Indonésie. Le cratère Kawah Ijen a un diamètre d'environ un kilomètre et contient un lac hyper acide (pH ~ -0.5) ainsi qu'une petite solfatare en dégazage actif, entourée d'une aire d'altération acide-sulfate beaucoup plus grande qui était exposée durant l'éruption phréato-magmatique du volcan en 1817. L'étude décrite dans cette thèse comprend l'échantillonnage et l'analyse chimique des gaz et de leurs produits de condensation (l'équivalent de surface des fluides magmatiques hydrothermaux ayant formé le minerai) recueillis dans la solfatare et des échantillons de roche pris dans centre de l'altération. Les gaz de fumerolles condensés (pH ~ -0.5) émis par la solfatare et échantillonés à des températures entre 330 et 495 °C contiennent jusqu'à 3 ppm Cu et 3.8 ppm As. Le centre de l'altération est caractérisé par des zones de silice résiduelle, d'alunite-pyrite et de kaolinite/dickite; selon la géothermométrie de l'alunite-pyrite, la zone s'est formée à des températures entre 200 et 300 °C. La minéralisation épithermale à forte sulfuration survient à cet endroit sous la forme de pyrite massive dans la veine hôte, contenant jusqu'à 200 ppb Au, 16 ppm Ag, 6800 ppm Cu et 3340 ppm As; ces éléments sont invisibles sous la plus forte résolution du microcope à balayage électronique, et donc apparaissent soit sous la forme de nano-particules soit en solution solide dans la pyrite. Le manuscrit du chapitre 3 résume les observations décrites ci-haut, supportant un modèle dans lequel des gaz très acides ont été condensés à ~ 250 m sous le plancher du cratère pré-1817 du volcan Kawah Ijen. Dans la région près de la source de vapeur, le ratio fluide/roche était extrêmement élevé et a eu pour résultat le lessivage d'éléments de la roche hôte andésitique, laissant derrière un résidu de silice vacuolaire. En s'éloingnant de la source, vers une zone ou le ratio fluide/roche est intermédiaire, les liquides condensés ont remplacé les minéraux primaires de l'hôte avec de l'alunite et de la pyrite. La zone kaolinite/dickite s'est formée dans un environnement où la roche était en tampon (faible ratio fluide/roche), dans la zone la plus éloignée de la source de vapeur. Les phases contenant soit or, argent ou cuivre étaient sous-saturés en liquides condensés, cependant ils étaient aptes à se concentrer par adsorption sur les surfaces des cristaux de pyrite en croissance. Les métaux ont été incorporés dans la pyrite soit en formant des nanoparticules de métal, soit par substitutions couples, ou par remplacement direct du Fe (Cu seulement). Cette thèse procure une vision nouvelle quant à la formation de dépôts épithermaux à forte sulfuration, en montrant, en particulier, que la minéralisation épithermale à forte sulfuration de métaux précieux peut se former directement à partir des gaz volcaniques condensés, et que les procédés d'altération et de minéralisation métallifère peuvent se produire simultanément.

The latest eruptive episode of Merapi volcano, Java, Indonesia, produced block-and-ash flows (BAFs) that affected the densely populated areas on the volcano's southern flank. The flows were not confined to the existing valleys but spilled over the valley sides to create overbank flows that resulted in fatalities and strong damages in the village of Kaliadem, -5 km away from the summit. This testifies the unpredictable behaviour of BAFs, not only at this volcano but also at similar locations around the world, and the need for an improved understanding of the flow transport and depositional mechanisms. In this respect, the new approaches, descriptive schemes and numerical simulations presented in this thesis address some of the key concepts of the dynamics and hazards of BAFs. The 2006 deposits were examined both immediately after flow emplacement and after the first rainy season following the eruption, allowing detailed correlations between their surface characteristics and internal architecture. Two main types of BAFs (short- to mediumrunout and long-runout BAFs) are recognized based on parameters including generation mechanism, flow volume, travel distance, deposit morphology, distribution, lithology and grain size distribution. The effects of topography on flow dynamics have been examined through the development of conceptual models for the two types of BAFs. Integration of high-resolution field-based data into numerical simulations using the Titan2D and VolcFlow models allows the validity of these models to be tested and rapid quantification of best-fit input parameters. Sensitivity analyses and inundation maps based on the probability of impact were used to produce a suite of potentially inundated areas from future collapse events affecting the Gendol valley and adjacent areas on the southern flank. Results provide the basis for defining hazard zonations of key areas at risk from BAFs at Merapi

The 2010 explosive eruption (VEI 4) of Merapi volcano, Indonesia, was the volcano’s largest since 1872. In contrast, volcanism over the last century has been characterised by dome-building and gravitational dome collapse, such as in 2006 (VEI 1). The driving forces behind effusive and explosive activity, as well as factors that affect transitions in eruptive style are investigated through petrological and textural analysis, using the well-documented 2006 and 2010 eruptions as case-studies. Pre- and syn-eruptive crystallisation and degassing processes are examined via whole rock geochemical analysis, mineral compositions and thermobarometry, quantitative textural analysis of feldspar microlites and analysis of volatiles and light lithophile elements in melt inclusions. These data were gathered from a detailed set of stratigraphically controlled samples, correlated to eruptive chronology and style, which were collected during several field campaigns. Both the 2006 and 2010 eruptions produced basaltic andesite, similar in terms of major and trace element compositions. A major zone of crystallisation is proposed at between ~ 14 and 29 km depth, although crystallisation occurs throughout the crust. Magmatic temperatures are estimated to be ~920–1020 °C. Maximum H2O contents reach 3.94 wt.% in 2010 melt inclusions and up to 3.73 wt.% in those from 2006. CO2 concentrations are < 200 ppm, although they may reach up to 695 ppm in some melt inclusions from the 2010 eruption. An exsolved brine phase was present during both eruptions which “buffered” melt Cl concentrations and enriched Li at shallow depths within the conduit or edifice. Eruptive style and transitions at Merapi are linked to magma ascent rate, crystallisation and open- and closed-degassing processes, which can be influenced by magma influx. The findings of this work are crucial for understanding the full range of eruptive behaviour that Merapi is capable of producing.

La geochimie isotopique du thorium, associee a celle de l'o, du sr et du nd et a des mesures precises des teneurs en u et th dans les roches volcaniques actuelles, permet d'etudier la genese et l'evolution des magmas dans plusieurs contextes geodynamiques. Les resultats essentiels de ce travail sont les suivants: 1) la mise en evidence, en islande, de l'importance des phenomenes de contamination crustale: l'assimilation de croute profonde se produit aussi bien dans les zones de rift (produisant des tholeiites a quartz normatif a partir de tholeiites a olivine), que dans la zone laterale sud de l'islande ou l'extension est quasi inexistante et ou les basaltes primaires sont des basaltes alcalins donnant apres contamination crustale des basaltes riches en fe, ti; 2) l'origine des roches acides en islande est a rechercher dans la fusion de la croute metabasique, parfois prealablement alteree par l'hydrothermalisme. Ce modele pourrait s'appliquer a la formation de la croute continentale primitive; 3) le volcan hekla, etudie en detail, montre les roles respectifs de la fusion crustale et de la cristallisation fractionnee dans la formation des laves, allant des andesites basiques aux rhyolites; 4) dans l'archipel des canaries, les magmas primaires derivent d'un melange de magmas venant d'une source appauvrie et d'une source de type tristan de cunha; 5) l'importance d'un composant sedimentaire dans les sources des magmas de zones de subduction a ete mise en evidence dans l'arc de la sonde, en indonesie et au chili. Dans ce dernier cas, une correlation entre l'enrichissement des magmas en u et #1#0be montre que ces deux elements sont apportes dans les magmas par des fluides issus de la deshydration des sediments subductes, quelques 20000 ans avant leur eruption a la surface

Basée sur trente mois d’enquête ethnographique, cette thèse porte sur un processus de réinstallation d’un village des hautes terres du volcan Merapi à Java centre en Indonésie à la suite de l’éruption de 2010. À travers l’étude diachronique et synchronique de ce processus, l’analyse montre qu’au-delà des changements sociaux, des reconfigurations socio-spatiales, des enjeux économiques et politiques que soulève la mise en place du programme de réinstallation par le gouvernement indonésien, des éléments significatifs de l’espace social villageois se sont maintenus : permanence des relations de proximité résidentielle, maintien de l’organisation et de l’unité sociale, maintien des liens à l’ancien territoire villageois et à la sylve environnante, ancrage spatial rituel similaire. Cette continuité, plusieurs années après la réinstallation, met en lumière l’existence de modes de territorialité spécifiques en lien avec le volcan. Ces modes s’inscrivent à la fois dans une histoire écologique longue, dans l’histoire des relations avec le pouvoir central et le pouvoir traditionnel régional ainsi que dans un rapport à la terre dans lequel l’entité volcanique est complètement intégrée à la vie sociale des humains. L’analyse de ce processus de réinstallation sur le long terme, selon une approche multiscalaire intégrant les relations que le village entretient avec l’extérieur, permet de montrer que l’incertitude inhérente au volcanisme de la région est socialement structurante et de surcroît, qu’elle façonne un milieu de certitude. C’est en ce sens que l’on peut parler, pour évoquer l’espace des hautes terres du volcan, d’une construction « volcanique » de l’espace social
Based on a thirty month ethnographic survey, this thesis focuses on a resettlement process of a Merapi volcano upland village (central Java in Indonesia) following the eruption of 2010. Through diachronic and synchronic approach of this process, this thesis shows that beyond social changes, socio-spatial reconfigurations, economic and political issues raised by the implementation of the resettlement program by the Indonesian government, significant elements of the village social space have been maintained : permanence of residential proximity relations, maintenance of organization and social unity, maintenance of relationswith the former village territory and with the surrounding forest, similar ritual spatial anchorage. This continuity, several years after the resettlement, highlights the existence of specific modes of territoriality related to the volcano. These modes are part of a long ecological history, of the history of relations with the central power and the traditional regional power as well as of a specific relationship to the land in which the volcanic entity is completely integrated into the human social life. The analysis of this long-term resettlement process, using a multi-scale approach integrating the village's relations with the outside world, shows that the uncertainty, inherent in the regional volcanism, is socially structuring and, in addition, that it shapes a milieu of certainty. It is in this sense that one can speak, to evoke the Merapi volcano upland space, of a "volcanic" construction of the social space.Keywords: Post-disaster resettlement, Social Space, Volcano, Java, Indonesia

abstract: Silicic volcanoes produce many styles of activity over a range of timescales. Eruptions vary from slow effusion of viscous lava over many years to violent explosions lasting several hours. Hazards from these eruptions can be far-reaching and persistent, and are compounded by the dense populations often surrounding active volcanoes. I apply and develop satellite and ground-based remote sensing techniques to document eruptions at Merapi and Sinabung Volcanoes in Indonesia. I use numerical models of volcanic activity in combination with my observational data to describe the processes driving different eruption styles, including lava dome growth and collapse, lava flow emplacement, and transitions between effusive and explosive activity. Both effusive and explosive eruptions have occurred recently at Merapi volcano. I use satellite thermal images to identify variations during the 2006 effusive eruption and a numerical model of magma ascent to explain the mechanisms that controlled those variations. I show that a nearby tectonic earthquake may have triggered the peak phase of the eruption by increasing the overpressure and bubble content of the magma and that the frequency of pyroclastic flows is correlated with eruption rate. In 2010, Merapi erupted explosively but also shifted between rapid dome-building and explosive phases. I explain these variations by the heterogeneous addition of CO2 to the melt from bedrock under conditions favorable to transitions between effusive and explosive styles. At Sinabung, I use photogrammetry and satellite images to describe the emplacement of a viscous lava flow. I calculate the flow volume (0.1 km3) and average effusion rate (4.4 m3 s-1) and identify active regions of collapse and advance. Advance rate was controlled by the effusion rate and the flow’s yield strength. Pyroclastic flow activity was initially correlated to the decreasing flow advance rate, but was later affected by the underlying topography as the flow inflated and collapsed near the vent, leading to renewed pyroclastic flow activity. This work describes previously poorly understood mechanisms of silicic lava emplacement, including multiple causes of pyroclastic flows, and improves the understanding, monitoring capability, and hazard assessment of silicic volcanic eruptions.
Dissertation/Thesis
Doctoral Dissertation Geological Sciences 2016

碩士
國立中央大學
地球科學學系
101
Volcanic tremor that follows explosive eruptions is an ubiquitous signal found in several volcanoes and also found at Semeru volcano, East Java, Indonesia. Twenty five episodes of volcanic tremor data from 22 November – 31 December 2009 have been analyzed using methods from the discipline of nonlinear dynamics in order to investigate their nonlinear dynamical properties. The phase space which describes the evolution of the behavior of nonlinear system was reconstructed from the original tremor seismograms using the delay embedding theorem suggest by Takens. The delay time used for reconstruction was selected after examining the autocorrelation function and average mutual information giving delay time in the range of 7-11. The false nearest neighbor method was applied to time data set yielding sufficient embedding dimension between 5-7. Exponential divergence of nearby orbits is the hallmark of chaotic behavior and was quantified by the maximal Lyapunov exponent (MLE). MLEs were found to vary as a function of the number of overtones in tremor signal and as a function of time. This implies that the tremor source fluctuates between a quasi-periodic state with few overtone frequencies and small MLEs (~0.013) and a chaotic one with more overtones and larger MLEs (up to 0.039). Estimation of attractor dimension was done using the correlation algorithm suggested by Grassberg and Procaccia. The events with the correlation dimension equal to or less than 2 likely have a torus as an attractor in the phase space. For events that have correlation dimension larger than 2, the trajectory is not bounded close to the torus and therefore it can explore a larger area of the phase space. No correlation dimension for some events can be explained due to dynamical correlations that persist for arbitrarily large data sets along a torus. Physical observations indicate that the tremor source involved gas escaping from the plug of conduit through one or more fractures. The properties of the plug probably played a very important role in determining the characteristics of the tremor signal.

碩士
國立成功大學
自然災害減災及管理國際碩士學位學程
105
In this thesis, a depth-averaged model in a terrain-fitted coordinate system is applied to simulate the pyroclastic flows during the eruption of Mt. Merapi in 2010. Through the numerical simulation we are able to obtain more precise flow information, such as the local flow fluxes, the distributions of flow depth and velocity as well as the deposits, for the goal of hazard mitigation or hazard management. In the numerical computation, the terrain-fitted coordinate system is based on the digital elevation model (DEM). Because of the fact that the real topography might consists of highly varying elevation, e.g. obstacles or cliffs, which is not applicable in the terrain-fitted coordinate, a compromised treatment is to smooth (filter) the topographic surface. However, the employment of the smooth basal surface might introduce deviation because of the lack of the sudden change of topography. In this study, we introduce the so-call “sub-topography” over the smoothed topographic surface, to mimic the real topography. In the simulations, we also introduce the “Upwelling” to mimic the exploded material, especially by the multiple eruptions, so that we may have a more reasonable spreading/supply of flow material. In addition, we also investigate the impacts of the key parameters on the flow behaviors, such as the friction coefficient, momentum correction factor and the amount of upwelling. Besides, the Voellmy rheology has also been taken into account. The results of these tests were compared to theoretical findings of rheological analysis presented in previous studies as well as historical records, and satellite images to figure out the representative values of the relevant parameters.