Effects of recent climate change on high mountains of western North America
Citation
Clague, John J., Effects of recent climate change on high mountains of western North America: Institute of Northern Engineering University of Alaska Fairbanks, v. 1, p. 269-274.
Summary
Pronounced step-wise atmospheric warming during the 20th century reduced ice cover in mountains by 25-50 percent. Net changes in average annual and mean summer temperatures responsible for this remarkable deglacierization are less than 2 degrees C, a small fraction of the warming that occurred at the end of the Pleistocene. Yet the effects of these changes on mountain landscapes have been profound. Alpine permafrost, which expanded during the Little Ice Age. now appears to be thinning and disappearing in many areas. Loss of alpine permafrost and glacier downwasting appear to be partly responsible for accelerated mass wasting and catastrophic rock-slope failures in high mountains. New lakes appeared during the Little Ice Age when glaciers [...]
Summary
Pronounced step-wise atmospheric warming during the 20th century reduced ice cover in mountains by 25-50 percent. Net changes in average annual and mean summer temperatures responsible for this remarkable deglacierization are less than 2 degrees C, a small fraction of the warming that occurred at the end of the Pleistocene. Yet the effects of these changes on mountain landscapes have been profound. Alpine permafrost, which expanded during the Little Ice Age. now appears to be thinning and disappearing in many areas. Loss of alpine permafrost and glacier downwasting appear to be partly responsible for accelerated mass wasting and catastrophic rock-slope failures in high mountains. New lakes appeared during the Little Ice Age when glaciers advanced across streams and rivers and blocked drainage. Most of these lakes drained one or more times during the 20th century, producing catastrophic floods orders of magnitude larger than normal nival or rainfall floods. In some instances, lakes have appeared upvalley of former, drained ones as glaciers have continued to retreat under a warming climate. Lakes also formed behind Little Ice Age end moraines when glaciers retreated in the early 20th century. Moraine dams are vulnerable to failure because they are steep-sided and consist of loose sediment. Outburst floods from lakes dammed by glaciers and moraines erode, transport, and deposit huge amounts of sediment over distances tens of kilometers. They broaden flood plains, destroy pre-flood channels, and create a new braided planform. The changes can persist for decades after the flood.