Electrical Resistivity Soundings of Glacier Beds: A Test Study on Grubengletscher, Wallis, Swiss Alps

Abstract

ABSTRA CT . Elec tri cal res isti vity sounding, usin g electrodes whic h are lowered direc tl y to th e ice-rock interface in bore holes, is proposed as a technique for stud ying the exact position of glacier beds, as well as their lithologica l ch a rac teristics. A test study is d escribed on G rubeng letscher, a pa rtially cold Alpin e glacier in Switzerl a nd. Res ul ts of so undings a long a 400 m long p rofil e indicate that previo us depth determina ti o ns, based on radio echo -soundings, were in gene ral accura te to w ithin less than 50/ 0 of the ac tu al ice thic kness. The resu lts also sho w th at the glacie r rests o n nonconsolid a ted sedimen ts of considera ble thi ckness. The proposed me thod could add substa nti al inform ati o n a bo ut g lacie r sliding a nd g la cier e rosion, if a pplied al o ngsid e conve ntional d ee p drilling projec ts. I NTRODUCTI ONThe beds of existing glaciers are characterized by a wide variety of morphological and lithological conditions . These beds may be rough or smooth depending on the scale considered, and they may consist of rock or unconsolidated sediments. Sediments at glacier beds mayor may not be frozen, and they mayor may not contain ground-water. To know what conditions exist at the glacier bed in a specific case is important for several reasons.Practical applications in connection with the planning and operation of Alpine hydroelectric power stations, such as the installation of subglacial water intakes or rock galleries for water adduction, may require the exact position and the lithological characteristics of glaCier beds (e.g . Bezinge and others, 1973;Vivian and Zumstein, 1973; Wold and 0strem, 1979). From a scientific point of view, knowledge about glacier bed characteristics is essentially relevant to studies done on glacier sliding, (Ll iboutry, 1979;Weertman, 1979;Iken, 1981; Iken and others, 1983) and to those which deal with processe~ of glacier erosion (Boulton, 1979;Collins, 1979;Rothlisberger and Iken, 1981).Commercial projects mainly utilize core drillings, either from the glacier surface downwards or from already existing rock galleries upwards, to probe the glaCier bed. Scientific studies have to try less expensive methods, such as hot-water drilling (e . g. Iken and others, 1977), geophysical soundings (Susstrunk, 1951;Rothlisberger, 1967;Robin, 1975) observations with bore-hole cameras (Engelhardt and others, 1978), or observations in ice tunnels (Boulton, 1979). All these methods furnish information of limited accuracy or point information only. This paper proposes a method by which it is hoped to be able partially to fill this gap: electrical resistivity soundings of glacier beds . Elektrisc he Widerstandssondierunge n mit El e ktrod en, di e in Bohrloche rn direkt a n d e r Eisunte rg re nze in stallie rt we rde n, wcrd en fU r die U nte rsuc hung d er genau en Lage und der lithologischen Charakteristik von G letscherbetten vorgeschl agen. Eine T estmess ung am G rubengletsche r, einem teil weise ka lte n Gletsche r der Schwe...

Modeling glacier thickness distribution and bed topography over entire mountain ranges with GlabTop: Application of a fast and robust approach

“…Concerning direct ice thickness measurements, GPR had started to replace earlier seismic soundings (cf., for instance Haeberli and Fisch [1984] and Narod and Clarke [1994]) and is now widely used [cf. Farinotti , 2010].…”

“…A critical step for the use of modeled glacier beds in other applications is the assessment of their quality, which requires validating them with ground truth data. For still existing glaciers, bedrock information can be derived from (hot‐water) drilling, geophysical soundings like ground penetrating radar (GPR) or – optimally – a combination of both [ Haeberli and Fisch , 1984]. Such reference information, however, is only sparsely available and in many cases biased toward crevasse‐free, flat and thus thick glacier parts with compressing flow [e.g., Frey et al , 2010].…”

A Critical Review of the Low-Frequency Electrical Properties of Ice Sheets and Glaciers

“…The presence of such sediments can be confirmed, their extent and thickness mapped, and hydromechanical changes within them detected, using borehole-based electrical resistivity soundings and SP measurements (e.g., Haeberli and Fisch, 1984;Brand et al, 1987;Engelhardt et al, 1990;Blake and Clarke, 1999). Kulessa et al (2003aKulessa et al ( , 2006b demonstrated that a combination of automated subglacial SP measurements and mathematical modelling together with 3-D inversion of time-lapse subglacial electrical resistivity data allows comprehensive characterisation of the hydraulic properties of and processes within subglacial sediments.…”

Subglacial electrical phenomena

“…Their aim was to examine the anisotropy, temperature, and density structure of the ice shelf and to infer conditions at the lower boundary where ice and seawater are in contact. More recently, Haeberli and Fisch [1984] and Brand et al [1987] have placed electrodes in boreholes in order to measure the resistivity of the glacier bed.…”