Grand Plateau Glacier starts on the north flank of Mount Fairweather in the Saint Elias Mountains and flows generally northwest for 19 miles (31 km) where it splits into two terminal lobes, with the southern lobe flowing 6 miles (10 km) to Grand Plateau Lake, about 142 miles (229 km) northwest of Juneau and 70 miles (113 km) southeast of Yakutat, Alaska. The northern terminal lobe flows for 10 miles (16 km) to Alsek Lake. Jean-François de Galaup, Comte de Lapérouse called this glacier Le Grand Plateau in 1786, and in 1875, William Healey Dall of the U.S. Coast and Geodetic Survey called it Grand Plateau Glacier when it terminated directly into the Gulf of Alaska. Mount Fairweather is part of the Fairweather Range, a mountain range located along the border between Alaska and British Columbia and is the southernmost range of the Saint Elias Mountains. The northernmost section of the Fairweather Range is situated in Tatshenshini-Alsek Provincial Park while the southernmost section is in Glacier Bay National Park. Mount Fairweather was named on May 3, 1778, by Captain James Cook, apparently for the unusually good weather encountered at the time. The Tlingit name for the mountain is Tsalxhaan. The peak has a summit elevation of 15,325 feet (4,671 m), which is the highest point in British Columbia, and it was first successfully climbed in 1931 by Allen Carpé and Terris Moore.
Grand Plateau Lake and Alsek Lake are proglacial lakes formed by the damming of glacial meltwater by a terminal moraine created by the retreat of Grand Plateau Glacier. Grand Plateau Glacier advanced during the Little Ice Age and terminated directly into the Gulf of Alaska. Maps from 1908 show no lake at the terminus of the glacier. By 1966, the glacier had retreated creating a moraine near the coastline and forming a proglacial lake. Since the 1980s, satellite images have been used to measure the glacier retreat. The first image was acquired on September 7, 1984, and a second image was acquired on September 17, 2019. Over this period of 35 years, the entire flow of the glacier system has changed with many of the glacier’s branches now redirected. Grand Plateau Glacier is also visibly narrowing and thinning, exposing more land as ice has pulled away from the valley margins. Continued shrinkage of Grand Plateau Glacier is virtually certain and thinning in the terminus region that separates Grand Plateau and Alsek Lakes is accelerating. Glacier monitoring and research show that continued retreat of the Grand Plateau Glacier will soon connect Alsek Lake and Grand Plateau Lake. This may potentially cause the Alsek River below Alsek Lake to go dry as the existing flow regime is abandoned resulting in a cascade of consequences.
The existing terminus of Grand Plateau Glacier separates Alsek Lake from Grand Plateau Lake. In response to thinning and retreat of that terminus, both lakes have more than doubled in size since 1958, and the two lakes are destined to join as one lake based upon recent trajectories of change. The Alsek River will then abandon its present flow regime to Dry Bay in favor of the much steeper outlet to Grand Plateau Lake. As a consequence, salmon habitat in the Alsek River will degrade as the flow becomes a sluggish, vegetation-choked clearwater stream surrounded by high brush and open forest. Other ecosystem-level impacts of the glacier retreat can be predicted, but there will also be consequential socioeconomic and cultural impacts from these changes. Human activities, institutions, and traditions have been built around the river’s existing flow regime and are threatened when it is redirected. Traditional and modern human activities centered on the Alsek River include commercial fishing, subsistence and sport hunting and fishing, and the finishing point for a world-renowned wilderness rafting expedition. The landscape-scale and ecosystem consequences of this change are substantial, even in the context of the rapidly evolving and largely glacier-covered southern coast of Alaska. Even more unusual for this sparsely populated region is the range of expected socio-economic impacts. Read more here and here. Explore more of Grand Plateau Glacier and Mount Fairweather here: