Slow surge of Trapridge Glacier, Yukon Territory ... - Glaciers Group

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Jun 20, 2006 - advanced 450 m and the glacier area increased by 10%, with an associated thinning of the ice. .... Steele, Hazard, Lowell, Hodgson, Disappointment, and .... data and digitize outlines of glaciers and snow patches. The.
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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, F03S32, doi:10.1029/2006JF000607, 2007

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Slow surge of Trapridge Glacier, Yukon Territory, Canada Tom-Pierre Frappe´1 and Garry K. C. Clarke1 Received 20 June 2006; revised 6 November 2006; accepted 27 December 2006; published 27 July 2007.

[1] Trapridge Glacier, a polythermal surge-type glacier located in the St. Elias Mountains,

Yukon Territory, Canada, passed through a complete surge cycle between 1951 and 2005. Air photos (1951–1981) and ground-based optical surveys (1969–2005) are used to quantify the modifications in flow and geometry that occurred over this period. Yearly averaged flow records suggest that the active phase began 1980, and lasted until 2000. The average velocity in the central area of the glacier went from 16 m yr1 in 1974 to 39 m yr1 in 1980; it peaked at 42 m yr1 in 1984, and remained above 25 m yr1 until 2001. Over that interval, the flow decelerated by steps, in 4-year pulses. After a particularly vigorous acceleration in 1997–1999, the glacier gradually slowed to presurge velocities. In 2005, the flow was less than 9 m yr1. Digital elevation models are generated by stereographic analysis of air photos for 1951, 1970, 1972, 1977, and 1981. These models are updated annually using ground-based survey data and a novel implementation of Bayesian kriging. Over the course of the surge, the front of active ice advanced 450 m and the glacier area increased by 10%, with an associated thinning of the ice. The previous surge of Trapridge Glacier, starting before 1939 and ending before 1951, led to a terminus advance of 1 km. Comparison of the two surges suggests that the 1930s surge started with a slow progression similar to what we observed in the 1980s and 1990s, and switched to a faster flow mode after 1941. This second phase was never attained in the recent surge, probably owing to a lack of mass. Citation: Frappe´, T.-P., and G. K. C. Clarke (2007), Slow surge of Trapridge Glacier, Yukon Territory, Canada, J. Geophys. Res., 112, F03S32, doi:10.1029/2006JF000607.

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[2] Trapridge Glacier (61°14 N, 140°14 20W), Yukon Territory, Canada was identified as a surge-type glacier by Austin Post and has received two cycles of scientific study. The first, in the 1930s and 1940s, coincided with an impressive, though poorly documented surge; the second, from 1969 to the present, spans the onset and termination of a weak surge with a long active phase. The surge began between 1974 and 1977 and had effectively ceased by 2005. The peak of the surge, 1984, was associated with a fourfold increase in flow rate relative to the presurge and postsurge quiescence. Total advance of the active front was 450 m, giving a maximum glacier length of 2.75 km. This displacement was much less than that of the previous surge (>1 km). [3] Meier and Post [1969] identified 204 surging glaciers in western North America, and outlined the following characteristics of surge behavior. (1) Surges occur repeatedly, and the duration of the cycle is generally constant for a single glacier. (2) Surges are short-lived (100 years, commonly 20 – 30 years). (3) The 1 Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, British Columbia, Canada.

Copyright 2007 by the American Geophysical Union. 0148-0227/07/2006JF000607$09.00

surge-phase average ice velocity can be 10– 100 times that of the quiescent phase. During the surge, ice drains rapidly from an upglacier reservoir area to a downglacier receiving area, causing thickness changes of 10– 100 m and horizontal displacements of