Glacier-Related Outburst Floods

doi:10.1016/B978-0-12-394849-6.00014-7

Snow and Ice-Related Hazards, Risks, and Disasters

Hazards and Disasters Series

2015, Pages 487-519

Snow and Ice-Related Hazards, Risks, and Disasters

https://doi.org/10.1016/B978-0-12-394849-6.00014-7 Get rights and content

Abstract

Water bodies impounded by glaciers and moraines can drain suddenly, with disastrous downstream consequences. Lakes can form at the margins of an alpine glacier or ice cap, on its surface, or at its base. Smaller pockets of water may also be present within some glaciers. In all cases, these ice-dammed water bodies might drain either via enlarging subglacial tunnels or by overtopping or mechanical collapse of the glacier dam. Most formerly stable glacier lakes failed over the past century, in many cases repeatedly, as glaciers downwasted and receded. The peak discharge, duration, and volume of an outburst flood resulting from subglacial tunnel enlargement depend mainly on the: (1) geometry and rate of development of the tunnel at the base of the glacier; and (2) size and geometry of the impounded water body. Discharge commonly increases exponentially during the outburst, but then decreases when either the drainage tunnel is plugged by collapse of the tunnel roof or closes due to plastic ice flow.

Most lakes dammed by lateral and end moraines formed in the twentieth century when valley and cirque glaciers retreated from advanced positions reached during the Little Ice Age. Moraine dams are susceptible to failure because they are steep and relatively narrow, they comprise loose poorly sorted sediment, and they may contain ice cores or interstitial ice. These dams generally fail by overtopping and incision. The triggering event might be a heavy rainstorm, strong winds, or an avalanche or landslide into the lake that generates waves that overtop the dam. Melting of moraine ice cores and piping are other possible failure mechanisms. Outflow from a moraine-dammed lake increases as the breach enlarges and then decreases as the level of the lake falls. The moraine breach may become armored, preventing further incision, or the hydraulic gradient at the breach may decrease to a point at which erosion ceases.

Outburst floods from glacier- and moraine-dammed lakes typically entrain, transport, and deposit large amounts of sediment. If the channel is steeper than about 6–9° and contains abundant loose sediment, the flood likely will transform into a debris flow. Such debris flows may be larger and more destructive than the flood from which they formed. A period of protracted atmospheric warming is required to trap lakes behind moraines and create conditions that lead to dam failure. The warming can also force glaciers to retreat, prompting ice avalanches, landslides, and jökulhlaups that have destroyed many moraine dams.

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Citation Excerpt :
Rapidly rising limbs also have been reported prior: Merzbacher Glacier Lake in the Tianshan (Ng, 2007; Shen et al., 2007); Russell Glacier in Greenland (Carrivick et al., 2017); Skeiðarárjökull and Grímsvötn glaciers in Iceland (Bjornsson, 2009; Clarke and Garry, 2003); Lowell and Steele Glacier in Yukon region in northwest Canada (Clarke, 1982). Thus, the hydrographs obtained for the Khurdopin Glacier Lake are compatible with theory and with other modeled results and monitored GLOFs (Bjornsson, 2009; Björnsson, 1998; Bjrnsson, 2003; Carrivick et al., 2017; Clague and Connor, 2015; Ng, 2007). The melt enlargement of the conduit dominated the evolution of the Khurdopin outburst floods, which enabled further determination of the contribution of m (melt rate) and S (cross-sectional area).
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Increasing cryospheric hazards in a warming climate
2021, Earth-Science Reviews
Citation Excerpt :
The moraine dams are susceptible to failure because they are steep and relatively narrow, and they are comprised of loose sediment, and even some ice. The moraine dams failure can be triggered by heavy rainstorm, strong winds, melting of moraine ice, avalanche or landslide that generates waves that overtop the dam (Clague and O'Connor, 2015). During a glacial lake outburst event, a large volume of water in these lakes can be discharged in a short period.
The cryosphere is an important component of the global climate system. Cryospheric components are sensitive to climate warming, and changes in the cryosphere can lead to serious hazards to human society, while the comprehensive understanding of cryospheric hazards largely remains unknown. Here we summarized the hazards related to atmospheric, oceanic and land cryosphere. The different types of cryospheric hazards, including their phenomena, mechanisms and impacts were reviewed. Our results suggested that: 1) The recorded hazards from atmospheric cryosphere including frost, hail, freezing rain decreased or showed great spatial heterogeneities, while their future changes are difficult to predict, and the extreme cold events in winter may increase in the future; 2) Sea ice extent declines rapidly, and iceberg numbers will increase. The permafrost-dominated coastline erosion will be exacerbated by climate warming. Meanwhile, the sea level rise is expected to continue in the next decades; 3) The glacier collapse, glacial lake outbursts and paraglacial readjustments will increase in the future. Although the total area of snow cover will decrease, the heavy snow events, snow avalanches, and snowmelt floods will not decrease simultaneously. The permafrost-related rock and debris flow and thaw slump will also increase with permafrost degradation. Taken together, we concluded the cryosphere is shrinking, while cryospheric hazards will likely increase in a warming climate.

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Chapter 14 - Glacier-Related Outburst Floods

Abstract