Geometric and thermal evolution of a surge-type glacier in its quiescent state: Trapridge Glacier, Yukon Territory, Canada, 1969–89

Abstract

ABSTRACT. Trapridge Glacier, Yukon Territory, Canada is a subpolar surge-type glacier. It last surged in the 1940s and is now in the late stages of quiescence. Since 1969, when the glacier was first surveyed, a large wave-like bulge has formed near the glacier terminus. Our surveys from 1969-89 show the profile evolution that has accompanied the formation and downflow propagation of this feature. Ice-temperature measurements taken in 1980-81 established that the bulge was forming at the boundary between thick warm-based ice lying up-glacier from the bulge, and thin cold-based ice lying down-glacier from it. The bulge is propagating at roughly 30 m a-I and thick ice has now completely overridden the region once covered by thin cold-based ice that we instrumented in 1980-81. In 1987, and again in 1988, the geographical positions of the 1980 measurement sites were redrilled and instrumented with new thermistor cables. Comparison of the 1980-81 data with that from 1987-88 shows that this region of the glacier has undergone a dramatic change in geometry and thermal regime. Water penetration into surface crevasses has warmed the 15-m ice temperature by roughly 2°C. The zone of transition from warm-to cold-based ice is migrating down-glacier but at a slower rate than that of the bulge feature. The transition from warm-based to cold-based ice appears to cause a discontinuity in the flow that resembles a transition from flow over a sliding boundary to flow over an adhering boundary. The discontinuity in the flow field is associated with anomalies in the temperature field and appears to be the source region for an englacial structure formed from subglacial sediment. This structure was not present in 1980-81 and is thought to have the geometry of a thrust fault or recumbent fold.

Slow surge of Trapridge Glacier, Yukon Territory, Canada

“…The temperature dependence of the flow parameter A follows the Arrhenius relation [see Paterson 1994, p. 86]. We took the thermal profile measured in hole 11C (1988) from Clarke and Blake [1991, Figure 9] as the standard profile and integrated equation (4) to obtain the corrected flow parameter A T = 5.75 × 10 −15 s −1 kPa −3 . Given that most of the deformation occurs in the basal ice, which for most of Trapridge Glacier is at the melting point, it is not surprising that this value is close to that tabulated for temperate glaciers, A (0°C) = 6.8 × 10 −15 s −1 kPa −3 , [ Paterson 1994, p. 96].…”

“…In addition to its unusual structure, the 1980s surge of Trapridge Glacier has the characteristic of having been observed as carefully from underneath as from the surface, and thus offers a unique context to test plausible surge models. Instrumentation of the glacier surface, interior, and base over the last 34 years yielded data sets and models for the thermal structure of the glacier [ Jarvis and Clarke , 1975; Clarke and Blake , 1991], its hydrology [ Stone and Clarke , 1993; Murray and Clarke , 1995; Stone and Clarke , 1996; Flowers and Clarke , 1999, 2002a, 2002b], and the hydro‐mechanical coupling at the bed‐ice interface [ Blake et al , 1992, 1994; Fischer et al , 1999; Fischer and Clarke , 2001; Kavanaugh and Clarke , 2001]. These are the key elements necessary to understand glacier flow, and have been used to inspire, parameterize, and test surge models [e.g., Fowler et al , 2001].…”

A quantitative framework for interpretation of basal ice facies formed by ice accretion over subglacial sediment

“…We make the assumption that an ice base experiencing long‐term freezing on a widespread basis will be in contact with subglacial sediment and that deep subglacial groundwater and water stored in the pore spaces of a till layer are the main (i.e., continuously present) sources of latent heat. This generalization may constitute an end‐member case, but it is plausible to assume that widespread basal freezing should inhibit development and maintenance of an organized subglacial drainage systems by promoting channel closure due to reduced water pressures and freezing on channel walls [ Clarke and Blake , 1991; Flowers and Clarke , 2002; Copland et al , 2003]. This should be particularly the case where basal freezing takes place beneath stopped ice streams, which still have relatively low horizontal water pressure gradients and thus small viscous heat dissipation that could counteract the effects of freezing and creep closure.…”

Black‐box modeling of the subglacial water system

“…Trapridge Glacier (Figure la) is a small surge-type subpolar glacier that has been subjected to extensive scientific study since 1969 [e.g., Jarvis and Clarke, 1975; Clarke et al, 1984;Clarke and Blake, 1991;Blake, 1992;Stone, 1993]. In summer 1992 we densely instrumented a region of the bed that included holes to both the connected and unconnected systems.…”