Recent History of Gulkana and College Glaciers Central Alaska Range, Alaska

Abstract

The Recent moraines of Gulkana and College Glaciers lie above tree line in the central Alaska Range and were dated by lichenometry as being deposited by advances in 1580(?), 1650(?), 1830, and 1875. Older moraines are also present, but could not be dated by this method. Gulkana Glacier advanced in 1580(?), depositing moraines which were partly buried by moraines of later advances. No correlative advance apparently occurred at College Glacier. Gulkana Glacier readvanced in 1650(?) and overrode the 1580(?) terminal moraine. In 1830 Gulkana Glacier advanced to a position 2.5 km. beyond the 1962 ice terminus, overriding 1650(?) moraines, spilling onto the Wisconsin glacial floor, damming College Creek, and partly blocking West Gulkana Creek canyon. With the blocking of College Creek, a small ice-dammed lake formed and was rapidly filled with outwash material from College Glacier. College Glacier also advanced in 1830 to a position 1.7 km. beyond its 1962 position. After a period of thinning and retreat, Gulkana Glacier advanced in 1875; no equivalent advance is recorded for College Glacier. The 1875 advance again blocked College Creek, and another small ice-dammed lake formed. Since 1875, both glaciers have rapidly thinned and retreated, indicating they have negative economies.