Juneau Icefield

The Juneau Icefield is an ice field located just north of Juneau, Alaska, continuing north through the border with British Columbia, and is the fifth-largest ice field in the Western Hemisphere, extending through an area of 3,900 square kilometres (1,500 sq mi) in the Coast Range ranging 140 km (87 mi) north to south and 75 km (47 mi) east to west. The icefield is the source of many glaciers including the Mendenhall Glacier and the Taku Glacier. The icefield is home to over 40 large valley glaciers and 100 smaller ones. The Icefield serves as a tourist attraction with many travellers flown in by helicopter for quick walks on the 240-to-1,400-metre (790 to 4,590 ft) deep ice and the massive, awe-inspiring moist crevasses. The icefield, like many of its glaciers, reached its maximum glaciation point around 1700 and has been in retreat since. In fact, of the icefield's 19 notable glaciers, the Taku Glacier is the only one presently advancing. Much of the icefield is contained within the Tongass National Forest. Since 1948, the Juneau Icefield Research Program has monitored glaciers of the Juneau Icefield. On the west side of the icefield, from 1946-2009, the terminus of the Mendenhall Glacier has retreated over 700 metres (0.43 mi).

Eight kilometers to the north, the Herbert Glacier has retreated 540 m (0.34 mi), while Eagle Glacier retreated 700 m (0.43 mi), Gilkey Glacier 3,500 m (2.2 mi) and Llewellyn Glacier 2,800 m (1.7 mi). On the south side of the icefield, the Norris Glacier retreated 1,740 m (1.08 mi), the East Twin Glacier 1,100 m (0.68 mi), the West Twin Glacier 570 m (0.35 mi) with only the Taku Glacier advancing. Surveys reveal the Taku as one of the deepest glaciers of the sub-temperate icefields surveyed at nearly 1,370 metres (4,490 ft) thick. This glacier was advancing in 1890 when viewed by John Muir and had a large calving front. By 1963 the glacier had advanced 5.6 km (3.5 mi). In 1948 the Taku Fjord had been completely filled in with glacial sediment and the glacier no longer calved. From 1948–1986 the glacier had a positive glacier mass balance driving the advance. From 1987–2009 the glacier has had a slightly negative mass balance, not enough to end the advance, but if it continues will soon slow it.

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