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 . Eight kilometers to the north, the Herbert Glacier has retreated , while Eagle Glacier retreated , Gilkey Glacier and Llewellyn Glacier . On the south side of the icefield, the Norris Glacier retreated , the East Twin Glacier , the West Twin Glacier with only the Taku Glacier advancing. Surveys reveal the Taku as one of the deepest glaciers of the sub-temperate icefields surveyed at nearly thick. This glacier was advancing in 1890 when viewed by John Muir and had a large calving front. By 1963 the glacier had advanced . 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.