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Ancient Data Provides Insights for Managing Future Flood Risks in Patagonia

New research provides insight into the history and current risks of glacier lake outburst floods, a major hazard in Chilean Patagonia. These findings were published by Elke Vandekerkhove, a PhD student in geology at Ghent University, in September in Quaternary Science Reviews.

Vandekerkhove explored the history of glacier lake outburst floods, looking back millennia before today’s climate crisis began, by studying sediments left over by ancient Patagonian floods. The study aimed to improve the flood record in Patagonia and, in the absence of a written record, the scientists turned to the earth itself. Vandekerkhove’s study reconstructed a 2,750-year flood record by honing in on the presence of specific sediments known to be deposited during these floods.

Glacier lake outburst floods (GLOFs) occur at the failure of a natural dam, made of ice or rock, which holds a lake of glacial meltwater. In these events, the water of the lake rushes out suddenly. GLOFs constitute a major threat in glacierized regions. In areas where people live, these uncontrollable flood events can send water plummeting towards communities, destroying infrastructure and causing the loss of livelihoods and lives. In places with low population densities, like the Baker River watershed in Chilean Patagonia studied by Vandekerkhove, the floods can disrupt pristine natural ecosystems. This type of flood has been particularly frequent in recent decades in Patagonia, making it an emblem for changing glacier systems.

GLOFs often occur in remote areas and people rarely witness them, but Columbia University senior research scientist Dorothy Peteet experienced one of the unstable glacial lakes that later burst in Akutat, Alaska. A glacier in that area, the Hubbard glacier, advanced so far that it blocked the outlet of the local Russell Fjord twice — once in 1986 and again in 2002, creating lakes that flooded the sides of the fjord for about a month and a half both times. Peteet told GlacierHub that before the flood outburst happened, she was in the lake that formed above the dam where she “had the chance to go by boat when it was flooded … floating over the tops of trees.”

To better understand the link between these floods and climate, Vandekerkhove and her colleagues analyzed floodplain sediment cores to generate a millennia-long flood record. Glacial sediment is deposited during each flood, with the more recent flood deposits overlying the older ones. The flood sediments could be distinguished in the sample, for they contain a high amount of inorganic material. At the selected sites, only the large (i.e., high-magnitude) floods are registered.

Patagonia glacier in Chile
An impressive Patagonia glacier in Chile. Over 80% of Latin America’s glaciers are in Chile. (Photo: Wallboat/Creative Commons)

In an email to GlacierHub explaining the study’s results, Vandekerkhove said “large GLOFs predominantly occur when glaciers are larger and thicker, at times when the climate is cooler and wetter.” However, she noted that the results “do not contradict the apparent recent increase of GLOFs due to rapid glacier retreat.”

“During glacier recession, glacial lakes and GLOF risk increase,” Vandekerkhove told GlacierHub. “Given the impact of GLOFs worldwide, a comprehensive understanding of the effect of climate change on GLOF occurrence is key to predicting the likely evolution under future climate conditions and to improving flood hazard assessments.”

A recent study shows that the Baker River, where Vandekerkhove’s study was conducted, reported six GLOFs in a two-year period, 2010-2012 — a rate which is unprecedented in the flood record for this area. The frequency of outburst floods are not only on the rise in Chilean Patagonia, but major GLOFs have also occurred in the Nepalese Himalayas, the mountains of Norway, the Bolivian Andes, the Kodar Mountains in Siberia, and the Karakoram Mountains, which extend through the bordering region of China, India, and Pakistan. Many of these occurrences were reported to be newfound or intensifying due to climate change, emphasizing the need for hazard management plans.

Vandekerkhove’s study has potentially important implications because it provides a historical lens and concrete evidence that can be used to support future hazard mitigation planning. A stronger understanding of the historical and future risk of GLOF hazards may support informed planning and subsequent development practices for local communities, like those near the Baker River watershed in Patagonia.

Long-term paleoflood records are crucial in generating better risk estimates since “instrumental data are very limited in time and thus insufficient to identify extreme events,” Vandekerkhove told GlacierHub. “Flood strategy and prevention should not be limited to frequent flood events but should also consider longer timescales to include larger past events.”

Accurate hazard and risk assessment are key for sustainable development worldwide, for a more complete ancient flood record offers insight into how these events have varied with the climate, which helps communities and decision-makers properly plan for the future.

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