Vít Vilímek

Glacier Retreat, Lakes Development and Associated Natural Hazards in Cordilera Blanca, Peru

Cordillera Blanca is the heaviest glacierized tropical range in the world. Due to the global climate change, most of glaciers are retreating and thinning. Glacier retreat leads to the formation and development of all types of potentially hazardous glacial lakes (bedrock-dammed, moraine-dammed, and ice-dammed). Potential hazardousness of glacial lakes is strongly interconnected with dynamic slope movements: (1) sudden release of water from glacial lakes (also known as glacial lake outburst floods—GLOF) is mainly caused by dynamic slope movement into the lake (about 80 % in the Cordillera Blanca); (2) released water may easily transform into debris-flow or mud-flow, thanks to its high erosion and transport potential. Based on field study and remotely sensed images, this contribution documents glacier retreat in the Cordillera Blanca with regards to formation and development of new potentially hazardous glacial lakes, which evolve mainly in elevations of about 4,600–5,000 m a.s.l. We introduce and describe three hazardous events associated with glacier retreat in the last decade: (a) sudden release of water from moraine-dammed Lake Palcacocha in 2003; (b) sudden release of water from bedrock-dammed lake No. 513 in 2010; and (c) sudden release of water from bedrock-dammed Lake Artizon Alto and subsequent moraine dam failure of downstream situated Lake Artizon Bajo in 2012. The first and third events were caused by landslides of lateral moraines (which are often non-consolidated and nearly vertical) into the lakes. The second event was caused by ice- and rockfall into the lake. These events illustrate that various natural hazards (dynamic slope movements, floods) associated with glacier retreat in the Cordillera Blanca are closely linked and represent actual threats to urbanization and safety of lives and property.

Limits and challenges to compiling and developing a database of glacial lake outburst floods

A unified database of glacial lake outburst floods (GLOFs) has been created for analysis and future natural hazard evaluations. The data from individual case studies fill the database at a primary level, while the regional and global scales are more suitable for evaluating the information. There is enhanced research activity in this topic worldwide due to ongoing environmental changes, and this is apparent in the database. Database compilation is linked to the International Programme on Landslides (IPL) because different types of slope movements are the most common triggering factors for glacial lake outburst floods, and the outburst floods, on the other hand, often initiate different types of slope movements.

Landslides in moraines as triggers of glacial lake outburst floods: example from Palcacocha Lake (Cordillera Blanca, Peru)

Studies focusing on moraine deposits which slide into glacial lakes are scarce, even though they can trigger impact waves responsible for generating glacial lake outburst floods. We focused on landslides in lateral moraines as possible triggers. Detailed geomorphological, geophysical, and satellite radar interferometric investigations of the Palcacocha Lake moraine (Cordillera Blanca, Peru) together with laboratory tests on samples from the site provided data for slope stability calculations using GeoSlope software and hydrodynamic impact wave modeling using the Iber code. We identified landslides that could affect Palcacocha Lake and calculated their stability (factor of safety) under specified conditions, including variable water saturation and earthquake effects. Calculations showed that the moraine slopes are close to the threshold value (Fs = 1) for stability and are especially sensitive to water saturation. The height of impact waves triggered by a landslide in 2003 and the potential wave heights from newly identified, possibly active landslides were calculated, based on landslide volume estimates, detailed lake bathymetry, and basin topography. Results show that potential future landslide-triggered waves could have similar properties to the 2003 impact wave. Evidence gathered in this study suggests that glacial lake outburst floods triggered by landslides from moraines, however, would be probably smaller than floods resulting from other types of slope processes (e.g., ice/rock avalanches) if dam breach is not taken into account. This assumption has to be critically evaluated against site-specific conditions at a given lake and any possible environmental factors, such as climate change or earthquake that may mobilize larger volumes of moraine material.

Hazard mitigation of glacial lake outburst floods in the cordillera blanca (Peru): The effectiveness of remedial works

Almost 40 glacial lakes have been remediated in the Cordillera Blanca since the 1940s by implementing different types of structural measures to prevent (mitigate) glacial lake outburst floods. These are (1) open cuts; (2) artificial dams; (3) tunnels; and their combinations. The first part of the paper provides an overview and description of the implemented remedial works. In the second part, the effectiveness of these remedial works is evaluated on the basis of a comparison of the quantified susceptibility of nine selected lakes to outburst floods before and after remediation. Our investigation showed that different types of remedial works have different impacts on the susceptibility of a given lake to outburst floods and are effective for different scenarios (causes and subsequent mechanisms) of outburst floods. Hazard management implications in the framework of risk management and ongoing geo-environmental change are also discussed.

Reactivation of mass movements in Dessie graben, the example of an active landslide area in the Ethiopian Highlands

Dessie town is located in a tectonic depression along the western rift margin with a young, high energy relief. Study area is known for numerous landslides in the past. These landslides are of different types, from shallow soil creeping to huge deep-seated landslides with appreciable consequences. Landslides endanger the quickly growing regional centre of Dessie and its infrastructure. Four typical recent landslides have been selected and studied in detail using both remote sensing and field observations from 2013. The described reactivation and new landslide events have been caused by a combination of natural influences and anthropogenic activities. Since seasonal rainfall is the main external triggering factor, precipitation data from Dessie weather station were analysed. The degree of negative human impact on slope instability was also discussed. Endangered zones and the actual risk in the studied localities were identified, and adequate measures were proposed.

Geomorphological Investigations at Machu Picchu, Peru (C101-1)

The landslide hazards analysis was the principal motivation to start geomorphological investigations in the area of Machu Picchu Sanctuary. But very soon, the need of a broader research was revealed, because the landscape evolution of the Urubamba River meander, where the archaeological site is located, is rather complex. Besides slope movements, also deepwards erosion, and selective mass wasting by weathering, suffusion etc. has been active there. Majority of them have been following predisposition by tectonical structure. Large-scale slope deformations have seriously affected mountain morphology in the area. The actual activity of those deformations is not well known yet, inspite that systematic monitoring has provided information as about irreversible movements on open cracks of rock outcrops within the archaeological site up to 1 mmyr-1 (lengths of time series is mostly 3 years), as about movement across the Main Plaza up to 6 mmyr-1. There still are other possibilities to explain those movements by ground deformation due to underground erosion along tectonically shattered zones, or by settlements of heavy stone buildings on water more saturated grounds.

Reassessment of the development and hazard of the Rampac Grande landslide, Cordillera Negra, Peru

BackgroundThe initial investigation analysed the complex Rampac Grande slope deformation from April 2009 (Landslides 8(3):309-320, 2011). The primary research in 2009 also identified an unrealistic explanation (raw mineral exploration) of the triggering of the landslide and the intention of the local authorities (from the administration centre of Carhuaz) to take measures to minimize the possible future risk to the local population. We also examined the adaptation measures introduced by the local authorities to reduce the risk for the local community.FindingsUnstable landslide material has been left after the 2009 event in the sources and transportation zone and several blocks were described as being only in a temporarily stable state. Landslide propagation could also follow the already existing lateral tension cracks identified in 2009. Areas of reactivation from 2012 were localized and triggering precipitation was evaluated.ConclusionThis study concluded that there is still a hazard of remobilization of specific parts of the landslide in Rampac Grande with potentially damaging effects on the buildings located close to the accumulation area.

Glacier-related landforms and glacial lakes in Huascarán National Park, Peru

The map of lakes and selected glacier-related landforms in Huascarán National Park was created describing their spatial distribution and selected properties related to their development. This work presents additional information on previous lake inventories that was not available prior to its completion despite the fact that some of the newly collected information is important for glacial lake flood hazard assessment. The ongoing environmental changes documented in the national park are affecting the number, size, spatial distribution and development of the glacial lakes. Many of the lakes are also filled with sediment, as well as subject to outburst floods. The lake typology is based on the character of their dam, whilst moraine ridge types are defined with specific geomorphological features that affect their stability. Over 1250 moraine ridges (longer than 200 m) were mapped and classified along with 2370 lakes each with a specific dam type. This represents the most detailed inventory which can be used for future statistical analysis or hazard assessment.

Debris Flows in the Vicinity of the Machu Picchu Village, Peru

The work summarizes information about spatial and temporal occurrence and damage caused by debris flows within last 50 years in the vicinity of the Machu Picchu village. Size and dynamic characteristics of limited number of events reveal, that two main classes of debris flows occurred in the study area. These classes are distinguished by specific triggering conditions, amount of delivered material to the main river valley (Urubamba River), duration time and speed. Incomplete weather information and debris flows allowed only preliminary comparison of relationship between rainfalls and debris flow occurrence. The results suggest coupling between 6-days preceding precipitation index and debris flow occurrence. Several low cost mitigation measures and risk management practices were suggested to reduce risk of the economically important area of the Machu Picchu village.

Morphological analysis and features of the landslide dams in the Cordillera Blanca, Peru

Global warming in high mountain areas has led to visible environmental changes as glacial retreat, formation and evolution of moraine dammed lakes, slope instability, and major mass movements. Landslide dams and moraine dams are rather common in the Cordillera Blanca Mountains Range, Peru, and have caused large damages and fatalities over time. The environmental changes are influencing the rivers’ and dams’ equilibrium, and the potential induced consequences, like catastrophic debris flows or outburst floods resulting from dam failures, can be major hazards in the region. The studies of past landslide dam cases are essential in forecasting induced risks, and specific works on this topic were not developed in the study region. Reflecting this research gap, a database of 51 cases and an evolution study of landslide dams in the Cordillera Blanca Mountains is presented. The main morphometric parameters and information of the landslide, the dam body, the valley, and the lake, if any, have been determined through direct and indirect survey techniques. Low variability in some of the main morphometric parameter distributions (valley width and landslide volume) has been shown, most likely due to an environmental control connected to the regional tectonic and glacial history. In order to analyze present and future landslide dam evolution, a morphological analysis was carried out using two recently developed geomorphological indexes employed on the Italian territory. The results of the Cordillera Blanca analysis have been compared with a large Italian landslide dam inventory, highlighting as much the differences as the similarities between the two datasets. The long-term geomorphological evolution changes are evaluated. Many of the stable dams are in disequilibrium with their surrounding environment and their classification result is of “uncertain determination.”