Slow surge of Trapridge Glacier, Yukon Territory, Canada

Abstract

[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 . Air photos (1951 -1981 and ground-based optical surveys 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 yr À1 in 1974 to 39 m yr À1 in 1980; it peaked at 42 m yr À1 in 1984, and remained above 25 m yr À1 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 yr À1 . 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.

Investigating changes in basal conditions of Variegated Glacier prior to and during its 1982–1983 surge

“…As shown in from a mean value of 10 % in winter 1973 up to 60 % for summer 1981 just before the surge started, confirming the values inferred by Raymond and Harrison (1988) using a simple model. Such progressive increase of the basal sliding during the quiescent phase might confirm, as suggested for slow-type surging glaciers by Frappé and Clarke (2007) for Trapridge glacier and Sund et al (2009) for Svalbard glaciers, that even for a fast-type surging glacier like Variegated, the surge phase is in fact the final phase of a progressive acceleration. Nevertheless, at the onset of the surge in winter 1981-1982, dramatic changes in the basal friction occur, principally in the upper part of the glacier.…”

A surge of the glaciers Skobreen–Paulabreen, Svalbard, observed by time-lapse photographs and remote sensing data

“…3). It is important to note that the surge front (the boundary between surging and non-surging ice) must have travelled downglacier considerably faster than this, as has been observed at other surging glaciers (e.g., Raymond et al 1987;Murray et al 2000;Frappe & Clarke 2007).…”

“…Few surging glaciers have been studied in detail, although it is clear that they can exhibit a very wide range of behaviour. Surges can be ''fast'' (with velocities of several kilometres per year) or ''slow'' (with velocities of a few tens of metres per year); they can affect both temperate and polythermal glaciers, and land-based and calving glaciers (Harrison & Post 2003;Murray et al 2003;Nolan 2003;Frappe & Clarke 2007).…”

Multi-year surface velocities and sea-level rise contribution of the Basin-3 and Basin-2 surges, Austfonna, Svalbard

“…at poly-thermal Bakaninbreen (Murray et al, 1998) and Trapridge glacier (Frappé and Clarke, 2007). Here, the surges started after driving stresses increased due to a gain of mass in the reservoir area which led to a positive feedback mechanism: more heat was generated at the bed, the glacier could flow faster, which then again lead to more strain heating and in the end to a switch from cold based to warm based conditions at the bed.…”