Hazards of a changing cryosphere: a comparison of glacial and paraglacial landscape responses to rapid glacial retreat in coastal fjords
Abstract
The impacts of climate change and glacier shrinkage pose a critical threat to mountain and coastal communities worldwide as freshwater resources dwindle, oversteepened slopes and proglacial basins destabilize and fail catastrophically, and sea levels rise. Identifying the signatures of how glaciers and landscapes respond to climate change is hence critical to predicting changes in water resources and natural hazards in the coming century.
Glacier thinning and retreat drives acceleration of glacier sliding and erosion, de-buttressing of steep valley walls, and destabilization of ice-marginal deposits and bedrock, which can lead to massive rock avalanching and accelerated incision of tributary watersheds. Compelling examples of these changes can be found from the recently deglaciated fjords of SE Alaska and the BC Coast Mountains due to the rapid thinning and retreat of temperate tidewater glaciers. Increased glacier sliding speeds leads to increased rates of subglacial erosion and the evacuation of any subglacially stored sediments into the proglacial basins, adding the the sediment loads of proglacial rivers. The shrinking glaciers also expose tributary watersheds to rapid paraglacial denudation processes driven by sharp drops in base level as glaciers termini retreat past the tributary outlets. More critically, glacier thinning exposes oversteepened, unstable slopes that can lead to massive tsunamigenic landslides, as happened in October 2015 at the terminus of Tyndall Glacier in Icy Bay, Alaska. Sediment yields measured from Tyndall Glacier, the landslide and tributary watersheds, and ongoing changes in glacier and fjord geometry using SfM photogrammetry are compared to surveys of the glacier and fjord collected pre- and post- landslide to investigate the frequency and magnitude of glacial and paraglacial responses to the rapid retreat of the glacier over the past half century. Between 1961 and 2016, basin-averaged denudation by the glacier and its non-glacial tributaries kept pace with retreat rates, and on par with each other, punctuated by the landslide. The sharp increases in sediment yields observed during retreat at Tyndall Glacier and other recently deglaciated fjords highlight the hazards associated with landscapes undergoing rapid glacier shrinkage due to climate change.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.C41D1493K
- Keywords:
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- 0702 Permafrost;
- CRYOSPHERE;
- 0720 Glaciers;
- CRYOSPHERE;
- 0742 Avalanches;
- CRYOSPHERE;
- 4333 Disaster risk analysis and assessment;
- NATURAL HAZARDS