The 2015 Chileno Valley glacial lake outburst flood, Patagonia

R Wilson,S Harrison,J Reynolds,A Hubbard,N.F Glasser,O Wündrich,P Iribarren Anacona,L Mao,S Shannon

doi:10.1016/j.geomorph.2019.01.015

Abstract

Glacial Lake Outburst Floods (GLOFs) have become increasingly common over the past century in response to climate change, posing risks for human activities in many mountain regions. In this paper we document and reconstruct the sequence of events and impact of a large GLOF that took place in December 2015 in the Chileno Valley, Patagonia. Hydrograph data suggests that the flood continued for around eight days with an estimated total discharge of 105.6 × 106 m3 of water. The sequence of events was as follows: (1) A large debris flow entered the lake from two steep and largely non-vegetated mountain gullies located northeast of the Chileno Glacier terminus. (2) Water displaced in the lake by the debris flow increased the discharge through the Chileno Lake outflow. (3) Lake and moraine sediments were eroded by the flood. (4) Eroded sediments were redistributed downstream by the GLOF. The post-GLOF channel at the lake outlet widened in some places by >130 m and the surface elevation of the terrain lowered by a maximum of 38.8 ± 1.5 m. Farther downstream, large amounts of entrained sediment were deposited at the head of an alluvial plain and these sediments produced an ~340 m wide fan with an average increase in surface elevation over the pre-GLOF surface of 4.6 ± 1.5 m. We estimate that around 3.5 million m3 of material was eroded from the flood-affected area whilst over 0.5 million m3 of material was deposited in the downstream GLOF fan. The large debris flow that triggered the GLOF was probably a paraglacial response to glacier recession from its Little Ice Age limits. We suggest that GLOFs will continue to occur in these settings in the future as glaciers further recede in response to global warming and produce potentially unstable lakes. Detailed studies of GLOF events are currently limited in Patagonia and the information presented here will therefore help to inform future glacial hazard assessments in this region.

Highlights

In response to climate change, many hazards associated with glacierised environments, such as ice/rock avalanches, landslides, debris flows and glacial lake outburst floods (GLOFs), have increased in prevalence over the past century, posing risks for human activities in mountain regions (Gruber and Haeberli, 2007; Keiler et al, 2010; Carrivick and Tweed, 2016)
We estimate that around 3.5 million m3 of material was eroded from the flood-affected area whilst over 0.5 million m3 of material was deposited in the downstream GLOF fan
We suggest that GLOFs will continue to occur in these settings in the future as glaciers further recede in response to global warming and produce potentially unstable lakes

Summary

Introduction

In response to climate change, many hazards associated with glacierised environments, such as ice/rock avalanches, landslides, debris flows and glacial lake outburst floods (GLOFs), have increased in prevalence over the past century, posing risks for human activities in mountain regions (Gruber and Haeberli, 2007; Keiler et al, 2010; Carrivick and Tweed, 2016). The most common triggering mechanism for moraine-dammed lake failures is overtopping, whereby waves produced by mass movements (e.g., snow and debris avalanches) or ice calving events breach the crest of a dam resulting in a progressive failure of the moraine structure (Clague and Evans, 2000; Huggel et al, 2004; Emmer and Cochachin, 2013; Rounce et al, 2016). The susceptibility of moraine dams to failure is influenced by threshold parameters such as the effective volume of lake water available for flood, dam freeboard height relative to lake level, the width/height ratio of the terminal moraine dam and the distal gradient of the dam structure (Reynolds, 2014)

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