GLOFs from moraine-dammed lakes: their causes and mechanisms V. Vilímek, A. Emmer Department of Physical Geography and Geoecology, Faculty of Science, Charles University, Prague, Czech Republic vilimek@natur.cuni.cz
Presentation structure I. GLOFs (introduction) II. Causes of GLOFs from moraine-dammed lakes - dam destruction x dam overflow - dynamic causes - long-term causes III. GLOFs in different regions - causes representation, time distribution with examples from Cordillera Blanca, Peru
I. Glacial lake outburst floods (GLOFs) Sudden water release from glacial lake (moraine-dammed, ice-dammed or bedrock) Peak discharge, high erosion and transport potential => catastrophic impacts Relation to various types of natural hazards (dynamic slope movements, earthquakes, extreme rainfalls) file:///c:/users/adam/desktop/škola/projekty/auc/nhess/figures/figure%203.jpg Huaraz, Peru, after outburst of Palcacocha Lake
II. Dam destruction x dam overflow Depends on the type of the dam (moraine x bedrocks) Morphometric parameters Etc. Palcacocha lake
The dam destruction (Palcacocha Lake, 1941) Before and after the outburst Significant sediment contribution through landslides, erosion etc. Damage
Lake ARTIZON BAJO, February 8th, 2012 10m 2011 The lake volume before the event (254,136 m 3 ) and after (105,592 m 3 ) The probable cause: landslide into the lake
The dam overflow GLOF from Laguna 513 (under Hualcán Mt.)
Flood modelling - Hualcán Mt. Model of the bridge with destroyed deck in HEC-RAS Cross section with possible landslide damming of the Chucchún River Photo of the bridge with deck destroyed during the flood event Plan view of the river centerline with cross sections (the blue lines show modeled water surface extents during the peak discharge) Flood lines enable identification of safe and endangered areas along the stream
Dam destruction
Dynamic causes of GLOFs Slope movement into the lake Earthquake Intensive rainfall / snowmelt Flood wave form lake situated upstream Blocking of underground outflow cannals
Slope movements into the lake Various types of dynamic slope movements (rock falls, landslides, ice falls, snow avalanches) into the lake lead to surge (displacement) wave, which may overflow or erode and thus destruct moraine dams
Ice falls Due to glacier retreat lake Palcacocha grows significantly
Only for illustration
Earthquake Large earthquake may initiate changes in internal structure of moraine dam and thus cause dam rupture or internal erosion (piping) Also slope movements may be initiated by an earthquake Conversely earthquake may stabilize moraine dam
Flood wave from lake situated upstream
Flood wave endangered the lake situated downstream
Long-term causes Buried ice melting Hydrostatic pressure impact Time effect (dam degradation) dam selfdestruction = combination of longterm causes, without any evident dynamic cause
III. Regional specifics of GLOFs In different regions, various causes are significant (based on our GLOFs database)
Time distribution is also regionally specific
@ North America rather well distributed through time Cordilera Blanca after 1970 there has been done a lot of work to improve safety Central Asia older events may not be known
GLOFs database Under construction Based on research into scientific literature and unpublished reports (ANA office, Huaraz, Peru) Events from all over the world opportunity for international cooperation Application for ICL Project this year (ICL = International Consortium on Landslides) More than one hundred events from across the globe currently online (http://prfdec.natur.cuni.cz/~kfggsekr/rggg/t-glof.html)
GLOFs database AIM: complete database with comprehensive information: lake type, probable cause of GLOF, flood volume, impacts (social and geomorphic), PURPOSE: Identification of regional differencies (specifics) of GLOFs => important step for creating optimal regionalfocused method of hazard assessment If any questions or comments, please use glofs.database@gmail.com or author email
Recent work - future aims Develop and fill GLOFs database Identification of regional-specifics Based on these data, create a new regionally-specific method of GLOF hazard assessment for Cordillera Blanca
Conclusions 1) GLOFs represent significant threat for inhabitants of high-mountain areas in these days of global climate change and glacial retreat 2) There are five dynamic and three long-term causes of moraine dam destruction with close relation to various types of natural hazards 3) The most frequent cause of GLOFs from morainedammed lakes is ice-fall into the lake, producing surge wave; other causes were registered with varied frequency
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