Academic literature on the topic 'Glacial erosion – Peru – Blanca, Cordillera'

Abstract. The Cordillera Blanca in Peru has been the scene of rapid deglaciation for many decades. One of numerous lakes formed in the front of the retreating glaciers is the moraine-dammed Lake Palcacocha, which drained suddenly due to an unknown cause in 1941. The resulting Glacial Lake Outburst Flood (GLOF) led to dam failure and complete drainage of Lake Jircacocha downstream, and to major destruction and thousands of fatalities in the city of Huaráz at a distance of 23 km. We chose an integrated approach to revisit the 1941 event in terms of topographic reconstruction and numerical back-calculation with the GIS-based open-source mass flow/process chain simulation framework r.avaflow, which builds on an enhanced version of the Pudasaini (2012) two-phase flow model. Thereby we consider four scenarios: (A) and (AX) breach of the moraine dam of Lake Palcacocha due to retrogressive erosion, assuming two different fluid characteristics; (B) failure of the moraine dam caused by the impact of a landslide on the lake; and (C) geomechanical failure and collapse of the moraine dam. The simulations largely yield empirically adequate results with physically plausible parameters, taking the documentation of the 1941 event and previous calculations of future scenarios as reference. Most simulation scenarios indicate travel times between 36 and 70 min to reach Huaráz, accompanied with peak discharges above 10 000 m3 s−1. The results of the scenarios indicate that the most likely initiation mechanism would be retrogressive erosion, possibly triggered by a minor impact wave and/or facilitated by a weak stability condition of the moraine dam. However, the involvement of Lake Jircacocha disguises part of the signal of process initiation farther downstream. Predictive simulations of possible future events have to be based on a larger set of back-calculated GLOF process chains, taking into account the expected parameter uncertainties and appropriate strategies to deal with critical threshold effects.

Abstract. One of the consequences of recent glacier recession in the Cordillera Blanca, Peru, is the risk of glacial lake outburst floods (GLOFs) from lakes that have formed at the base of retreating glaciers. GLOFs are often triggered by avalanches falling into glacial lakes, initiating a chain of processes that may culminate in significant inundation and destruction downstream. This paper presents simulations of all of the processes involved in a potential GLOF originating from Lake Palcacocha, the source of a previously catastrophic GLOF on 13 December 1941, killing about 1800 people in the city of Huaraz, Peru. The chain of processes simulated here includes (1) avalanches above the lake; (2) lake dynamics resulting from the avalanche impact, including wave generation, propagation, and run-up across lakes; (3) terminal moraine overtopping and dynamic moraine erosion simulations to determine the possibility of breaching; (4) flood propagation along downstream valleys; and (5) inundation of populated areas. The results of each process feed into simulations of subsequent processes in the chain, finally resulting in estimates of inundation in the city of Huaraz. The results of the inundation simulations were converted into flood intensity and preliminary hazard maps (based on an intensity-likelihood matrix) that may be useful for city planning and regulation. Three avalanche events with volumes ranging from 0.5 to 3 × 106 m3 were simulated, and two scenarios of 15 and 30 m lake lowering were simulated to assess the potential of mitigating the hazard level in Huaraz. For all three avalanche events, three-dimensional hydrodynamic models show large waves generated in the lake from the impact resulting in overtopping of the damming moraine. Despite very high discharge rates (up to 63.4 × 103 m3 s−1), the erosion from the overtopping wave did not result in failure of the damming moraine when simulated with a hydro-morphodynamic model using excessively conservative soil characteristics that provide very little erosion resistance. With the current lake level, all three avalanche events result in inundation in Huaraz due to wave overtopping, and the resulting preliminary hazard map shows a total affected area of 2.01 km2, most of which is in the high hazard category. Lowering the lake has the potential to reduce the affected area by up to 35 %, resulting in a smaller portion of the inundated area in the high hazard category.

Abstract. This paper studies the lake dynamics for avalanche-triggered glacial lake outburst floods (GLOFs) in the Cordillera Blanca mountain range in Ancash, Peru. As new glacial lakes emerge and existing lakes continue to grow, they pose an increasing threat of GLOFs that can be catastrophic to the communities living downstream. In this work, the dynamics of displacement waves produced from avalanches are studied through three-dimensional hydrodynamic simulations of Lake Palcacocha, Peru, with an emphasis on the sensitivity of the lake model to input parameters and boundary conditions. This type of avalanche-generated wave is an important link in the GLOF process chain because there is a high potential for overtopping and erosion of the lake-damming moraine. The lake model was evaluated for sensitivity to turbulence model and grid resolution, and the uncertainty due to these model parameters is significantly less than that due to avalanche boundary condition characteristics. Wave generation from avalanche impact was simulated using two different boundary condition methods. Representation of an avalanche as water flowing into the lake generally resulted in higher peak flows and overtopping volumes than simulating the avalanche impact as mass–momentum inflow at the lake boundary. Three different scenarios of avalanche size were simulated for the current lake conditions, and all resulted in significant overtopping of the lake-damming moraine. Although the lake model introduces significant uncertainty, the avalanche portion of the GLOF process chain is likely to be the greatest source of uncertainty. To aid in evaluation of hazard mitigation alternatives, two scenarios of lake lowering were investigated. While large avalanches produced significant overtopping waves for all lake-lowering scenarios, simulations suggest that it may be possible to contain waves generated from smaller avalanches if the surface of the lake is lowered.

The article presents a conceptual approach for the spatiotemporal distribution pattern of principal lake types in the context of the glaciation history in the Cordillera Blanca. The tropical mountain range hosts one of the main concentrations of proglacial lakes in high-mountain settings worldwide, which have formed as a result of the dominant trend of modern glacier retreat. In the 20th century, glacial lake outbursts have severely affected large settlement areas in the Rio Santa Basin. Additionally to the striking newly emerged lakes, geomorphological evidence of paleolakes is found throughout the middle and lower valley sections. Based on empirical data from field research in over 20 valleys and the analysis of air and satellite images, the study provides a genetic classification of major lake types and a generalized model for the distribution of the present lakes and paleolakes. The origin of the lakes and their recurrent distribution pattern are associated with the individual stages of the Pleistocene to modern glaciation and their corresponding geomorphological landforms. Apart from the individual lake, the focus is put on the spatial arrangement of the lakes to each other based on a holistic landscape assessment. Implications are drawn for the hazard potential, in particular in terms of outburst cascades involving two or more lakes. On a supraregional scale, a clustering of certain lake types occurs in different mountain ranges of the Andes according to their specific topographical and glaciological settings. Even though the glaciated areas have all been subject to major ice losses, only some mountain regions are prone to form moraine-dammed lakes such as in the Cordillera Blanca. The key controlling factors for their formation are highlighted from a glacial-geomorphological point of view. The distribution of principal types of glacial lakes is outlined in a N–S profile along the Andes.

Abstract. This paper presents a new and easily repeatable objective method for assessing the potential hazardousness of glacial lakes within the Peruvian region of Cordillera Blanca (excluding ice-dammed lakes, which do not reach significant volumes in this region). The presented method was designed to meet four basic principles, which we considered as being crucial. These are: (a) principle of regional focus; (b) principle of objectivity; (c) principle of repeatability; and (d) principle of multiple results. Potential hazardousness is assessed based on a combination of decision trees for clarity and numerical calculation for objectivity. A total of seventeen assessed characteristics are used, of which seven have yet to be used in this context before. Also, several ratios and calculations are defined for the first time. We assume that it is not relevant to represent the overall potential hazardousness of a particular lake by one result (number), thus the potential hazardousness is described in the presented method by five separate results (representing five different glacial lake outburst flood scenarios). These are potentials for: (a) dam overtopping resulting from a dynamic slope movement into the lake; (b) dam overtopping following the flood wave originating in a lake situated upstream; (c) dam failure resulting from a dynamic slope movement into the lake; (d) dam failure following the flood wave originating in a lake situated upstream; and (e) dam failure following a heavy earthquake. All of these potentials theoretically range from 0 to 1. The presented method was verified on the basis of assessing the pre-flood conditions of seven lakes which have produced ten glacial lake outburst floods in the past and ten lakes which have not. A comparison of these results showed that the presented method successfully identifies the potentially hazardous lakes.

As climate change continues to drive glacier retreat in the Cordillera Blanca, Peru, the fraction of dry season runoff derived from groundwater baseflow is increasing. Therefore, it is necessary to improve our understanding of proglacial hydrogeology to forecast how groundwater can offset decreasing meltwater resources. Unfortunately, little is known about high-elevation groundwater, the physical hydrogeological properties of aquifers, or contributions to stream flows in the Cordillera Blanca, Peru. This thesis addresses these knowledge gaps and presents the results from a groundwater investigation of two glaciated watersheds in the Cordillera Blanca during the July 2012 dry season. Investigative techniques include drilling with a portable drill, slug tests to measure permeability, and hydrochemical mixing model analysis. In the Llanganuco Pampa, glaciofluvial outwash and glacial till aquifers were identified with hydraulic conductivities of 10-4 and 10-5 m/s and groundwater flow velocities of 0.62 and 0.09 m/day, respectively. In the Quilcayhuanca Pampa, a buried talus aquifer was identified with an average hydraulic conductivity of 10-5 m/s and an average groundwater flow velocity of 0.10 m/day. The buried talus aquifer extended across the valley and was hydraulically connected to recent talus slope deposits along the valley side. Talus slopes are ubiquitous features in the Cordillera Blanca and the results presented here show that they are a significant pathway for groundwater recharge of valley aquifers and springs. Tracers from surface water and groundwater samples were used in a binary mixing model to estimate tributary and groundwater contributions to stream flow. Groundwater contributions to stream flow were 18% in the Llanganuco Upper Pampa and 21% in the Quilcayhuanca Pampa. These results suggest that discharge from the studied valley aquifers are a crucial component of dry season stream flow in the Cordillera Blanca. Further research is still needed to identify and quantify the sources of groundwater recharge (i.e. precipitation, glacial meltwater, and/or bedrock fracture flow) to better understand the ability of groundwater to buffer dry season flows in the context of melting glaciers.
Pendant que le retrait des glaciers de la Cordillera Blanca, Pérou, se poursuit à cause des changements climatiques, la part des eaux de ruissèlement provenant du débit de base des eaux souterraines augmente durant la saison sèche. Par conséquent, il est nécessaire d'améliorer nos connaissances en hydrogéologie périglaciaire afin de prévoir comment les eaux souterraines peuvent compenser la diminution des ressources en eaux de fontes. Malheureusement, les propriétés physico-hydrogéologiques des eaux souterraines de hautes altitudes, ainsi que leur contribution à l'écoulement des cours d'eau de la Cordillera Blanca, Pérou, sont très largement incomprises. Cette thèse présente les résultats de l'étude des eaux souterraines dans deux bassins versants de la Cordillera Blanca, menée en juillet 2012 durant la saison sèche. Pour se faire, les techniques d'investigation incluent des forages à la foreuse portative, des essais de perméabilité et des analyses de modèles hydrogéochimiques de mélange. Dans la Pampa Llanganuco, Il a été évalué que les aquifères d'épandages fluvio-glaciaires et de tills glaciaires atteignent respectivement des conductivités hydrauliques de 10-4 et 10-5 m/s et des vitesses d'écoulement d'eaux souterraines de 0.62 et 0.09 m/jour. Dans la Pampa Quilcayhuanca, le système aquifère de talus a été identifié avec, en moyenne, une conductivité hydraulique de 10-5 m\s et une vitesse d'écoulement d'eaux souterraines de 0.10 m/jour. Ce système s'étend à travers la vallée tout en étant hydrauliquement relié aux récents dépôts de débris rocheux le long des flancs. Les résultats présentés ici montrent l'omniprésence des dépôts de débris rocheux dans la Cordillera Blanca ainsi que leur importance dans la recharge des aquifères et des sources de la vallée. Les traceurs dans les échantillons d'eaux de surface et d'eaux souterraines ont été utilisés dans un modèle mixte à deux composantes pour estimer la contribution des affluents et des eaux souterraines dans l'écoulement du cours d'eau principal. La contribution des eaux souterraines à l'écoulement du cours d'eau était de 18% dans la Pampa Llanganuco et 21% dans la Pampa Quilcayhuanca. Ces résultats suggèrent que les eaux souterraines, provenant des aquifères des vallées, représentent une part importante de l'écoulement des cours d'eau durant la saison sèche dans la Cordillera Blanca. De plus amples recherches sont cependant nécessaires pour identifier et quantifier les sources de recharge en eaux souterraines (précipitations, eaux de fontes glaciaires et/ou écoulement dans les fractures du substrat rocheux) afin de mieux comprendre la capacité des eaux souterraines à entretenir l'écoulement des cours d'eau durant la saison sèche dans le contexte de la fonte des glaciers.

Both tectonics and climate profoundly influence orogenisis, but specifics regarding the forcings, interactions and feedbacks are still largely unclear. This study addresses the evolution of the Cordillera Blanca Mountain Range of northern Peru: an elevated, high-relief, 200 km long string of glaciated peaks comprising the spine of the Andes. Extension along the Cordillera Blanca Detachment Fault (CBDF) actively produces relief along the western flank of the range, exceeding several kilometers in many areas. Abundant records of past glaciations span from >440 ka to the present in the form of moraine and bog deposits. Thus, tectonics (active faulting) and climate (glacial erosion) are operating in tandem to produce some of the highest topography in the western hemisphere. Understanding these processes in the Cordillera Blanca will provide an invaluable perspective into tectonic and climatic effects on orogenisis.Through the combined use of cosmogenic 10Be, low temperature thermochronology and digital terrain analysis, I explore the erosional and morphologic history of the range over a variety of spatial and temporal scales. Significant variations in modern range elevation (maximum, mean, modal and minimum), relief (local and within basins) and slope (maximum, mean and minimum) exist along the strike of the range, potentially reflecting the combined effects of variable displacement along the CBDF and varying degrees of glacial erosion. The morphology of the adjacent supradetachment basin varies as well, containing zones with distinct styles of faulting and basin growth, likely defined in part by the segmentation history of the CBDF. By combining Holocene-scale 10Be basin-averaged erosion rates with new thermochronologic data, I expand the known denudation history of the range. These two datasets constrain the exhumation and erosional history of the range-forming Cordillera Blanca Batholith from the late Miocene to Holocene, and expand the thermal history of the range southwards to include the older Carhuish Stock. Two new vertical 10Be exposure age transects allow comparison of fluvial incision rates within the Cordillera Blanca Batholith and the older Coastal Batholith. Incision rates from the site in the Cordillera Blanca record uplift on the order of ~1 mm yr-1, and potentially place a minimum constraint on CBDF slip rates at this location. Incision rates from the Coastal Batholith are twice as fast (~2 mm yr-1) possibly representing large-scale regional uplift. Exhumation rates and erosion rates generally fall between 0.01 and 0.5 mm/yr, suggesting a fairly continuous state of erosion over long-term (10^6 yrs) to recent (<10^3 yrs) time scales. Aside from a seemingly isolated zone of elevated erosion rates, no trends are observed along the strike of the mountain range. As the CBDF is believed to display variable slip-rates along strike, it seems that associated base level lowering is not a first order control on basin-averaged erosion rate.
Bien qu'il soit établi que la tectonique et le climat influencent profondément l'orogénèse, plusieurs questions demeurent en ce qui a trait aux forçages, interactions et rétroactions. Cette étude se penche sur l'évolution de la cordillère Blanche, dans le nord du Pérou : une chaîne de sommets glacés à haut relief de 200 km de longueur, épine dorsale des Andes. L'extension le long de la faille de détachement de la cordillère Blanche (FDCB) cause la formation de relief sur le flanc ouest de la chaîne sur plusieurs kilomètres dans certaines zones. D'abondantes traces de glaciations passées, datant de plus de 440 ka jusqu'à la période actuelle, sont présentes sous forme de dépôts de moraines et de tourbières. Donc, la tectonique (mouvements de failles actives) et le climat (érosion glaciaire) opèrent en tandem pour produire l'une des topographies les plus accidentées de l'hémisphère ouest. Une évaluation pointue des procédés en cause dans la cordillère Blanche permettra une meilleure compréhension des effets de la tectonique et du climat sur l'orogénèse. En utilisant une combinaison de datation par l'isotope cosmogénique 10Be, de thermo-chronologie de basse température et d'analyse de modèles numériques de terrain, cette étude explore l'historique d'érosion et morphologique de la chaîne sur plusieurs échelles spatiales et temporelles. De variations significatives d'altitude moderne de la chaîne (maximale, moyenne, modale et minimale), de relief (local et en bassin) et de pente (maximale, moyenne et minimale) existent le long de la chaîne et sont potentiellement dues aux effets combinés de mouvements variables le long de la FDCB et de différents degrés d'érosion glaciaire. La morphologie du bassin de supra-détachement adjacent varie également et contient des zones dotées de styles distincts de faille et de développement de bassin, probablement définis en partie par l'historique de segmentation de la FDCB. En combinant les rythmes d'érosion (âges 10Be, moyennes de bassin à l'échelle holocène) avec de nouvelles données thermo-chronologiques, ces travaux augmentent l'étendue connue de l'historique de dénudation de la chaîne. Ces deux bases de données documentent l'historique d'exhumation et d'érosion du batholithe de la cordillère Blanche depuis la fin du Miocène jusqu'à l'Holocène et étendent l'historique thermal de la chaîne vers le sud pour inclure le plus ancien Carhuish Stock. Deux coupes d'âges d'exposition verticale par 10Be permettent une comparaison des rythmes d'incision fluviale au sein du batholithe de la cordillère Blanche et du plus ancien batholithe côtier. Les rythmes d'incision au site de la cordillère Blanche indiquent un soulèvement d'environ 1 mm par an et suggèrent un glissement minimal de la FDCB de cet ordre à cet endroit. Les rythmes d'incision au batholithe côtier sont deux fois plus rapides (~2 mm par an), possiblement dû à un soulèvement d'échelle régionale. Les rythmes d'exhumation et d'érosion sont généralement de 0.01 à 0.5 mm par an, indiquant une érosion continue sur le long (10^6 années) et court terme (<10^3 années). Outre une zone isolée de rythmes d'érosion apparemment élevés, aucune tendance n'est observée le long de la chaîne de montagnes. Comme la FDCB est connue pour ses rythmes de glissement variables le long de la chaîne, il semble que l'abaissement du niveau de base associé ne soit pas un contrôle de premier ordre sur les rythmes d'érosion moyens à l'échelle du bassin.

Declines in glacier area and volume are widespread. These changes will have important hydrologic consequences since glaciers store tremendous amounts of fresh water and buffer seasonally low flows in many densely populated regions. In this thesis I focus on a region that is hydrologically vulnerable to glacier change, namely the Cordillera Blanca, Peru. I present three manuscripts that focus on measuring glacier area change, modeling the effect of this area change on the hydrology of one watershed, and isotopic sampling to elucidate hydrologic processes in this watershed and the entire Cordillera Blanca. In the first manuscript, I describe a methodology for mapping glaciers using satellite imagery. Satellite data, in conjunction with automated glacier mapping methods, are being used more frequently to map changes in glacier size. In contrast to the majority of studies using automated methods, I correct satellite images for atmospheric effects. Mapping glaciers with atmospherically-corrected satellite images resulted in an approximately 5% increase in glacier area, relative to glaciers mapped with non-atmospherically-corrected images. I also applied a consistent threshold that was validated using high-resolution satellite imagery. This helps to reduce error associated with change analysis. For the entire Cordillera Blanca, I calculated a 25% decrease in glacier area from 1987 to 2010. The rate of glacier area loss has increased significantly based on the most recent estimates. In the second manuscript, I use a physically-based, hydrologic model, the Distributed Hydrology Soil Vegetation Model (DHSVM) with a newly-coupled dynamic glacier model to simulate stream discharge and glacier change in the Llanganuco watershed of the Cordillera Blanca. I also examined statistical trends associated with historical records of temperature, precipitation, and discharge. I observed significant positive trends in annual temperature, but no trends in precipitation or discharge despite a 25% reduction in glacier area in this watershed over the same time. The model setup process and the results of sensitivity analyses are described. Of the input parameters I examined, I found that the model was particularly sensitive to changes in albedo and precipitation. Based on established efficiency criteria, the newly-coupled model did a decent job of simulating historical stream discharge and glacier area during 10 year calibration and validation periods. However, due to the lack of additional validation data and an inability to quantify uncertainty associated with model output, the model is not yet ready to be used for predicting future discharge based on different climate projections. In the third manuscript I describe the knowledge gained about hydrologic processes from isotopic sampling in the Llanganuco watershed, as well as other watersheds of the Cordillera Blanca. Thirty water samples from Llanganuco were collected in July 2011 and measured for stable isotopes of water, δ¹⁸O and δ²H. I first calculated the isotopic lapse rate, or the relationship between isotopic values and elevation. Lapse rates from this watershed are slightly more positive than global averages. This observation is best explained by the influence of glaciers. I also calculated the strength of the relationship between isotopic values and percent glacier cover. For Llanganuco, glacier cover is a better predictor of isotopic value than elevation. Based on examination of the same relationships at larger scales in the Cordillera Blanca, this relationship appears to be persistent at a regional scale. Finally, I used a simple two-component mixing model to estimate the relative contributions of glacier meltwater and groundwater in the Llanganuco watershed. Glacier meltwater made up approximately three-fourths of surface water that exited the watershed during this two week period in July, 2011. The importance of glacier meltwater is clearly demonstrated using stable isotopes, but further, more detailed monthly sampling is necessary to accurately determine annual and dry season streamflow contributions from glacier meltwater and groundwater.
Graduation date: 2013

Glacial-dominated areas pose unique challenges to downstream communities in adapting to recent and continuing global climate change, including increased threats of glacial lake outburst floods (GLOFs) that have substantial impacts on regional social, environmental and economic systems increasing risk due to flooding of downstream communities. In this dissertation, two lakes with potential to generate GLOFs were studied, Imja Lake in Nepal and Palcacocha Lake in Peru. At Imja Lake, basic data was generated that allowed the creation of a conceptual model of the lake. Ground penetrating radar and bathymetric surveys were performed. Also, an inundation model was developed in order to evaluate the effectiveness of a project that seeks to reduce flooding risk by lowering the lake at least 3 meters. In Peru, a GLOF inundation model was created. Also, the vulnerability of the people living downstream in the City of Huaraz was calculated, and the impacts of an early warning system were evaluated. The results at Imja indicated that the lake deepened from 98 m in 2002 to 116 m in 2012. Likewise, the lake volume increased from 35.8 to 61.6±1.8 million m3 over the past decade. The GPR survey at Imja and Lhotse-Shar glaciers shows that the glacier is over 200 m thick in the center of the glacier. The modeling work at Imja shows that the proposed project will not have major impacts downstream since the area inundated does not reduce considerably unless the lake is lowered by about 20 m. In Huaraz, the results indicate that approximately 40646 people live in the potentially inundated area. Using the flow simulation and the Peru Census 2007, a map of vulnerability was generated indicating that the most vulnerable areas are near the river. Finally, the potential number of fatalities in a worst case GLOF scenario from Lake Palcacocha was calculated to be 19773 with a standard deviation of 1191 if there is no early warning system and 7344 with a standard deviation of 1446 people if an early warning system is installed. Finally, if evacuation measures are improved the number reduces to 2865 with a standard deviation of 462.
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