Abstract:ABSTRACT. A bri ef d escrip tion o f t he resistivity method is given , stressi ng the p oints wh ich a re of pa r ticu la r im po rta nce when working on g laciers. Th e literature is bri efl y reviewed . R EsUME. l\1esllre de la risistivite de la glace et sondages ilectriques: Remarqlles /Jreliminaires. La me th od e des resisti vites est d ecrite d e fa<;:on som m a ire et les points particu li ers it son a p pli cat ion su r les g laciers sont mi s en ev idence. U ne breve revue de la li ttera ture es t pr… Show more
“…The resistivity of the surface ice layer (3.5 Mn m) is a factor of twenty higher than that of any surface layer on George VI Ice Shelf. It lies within the range of resistivities for the surface layers of temperate glaciers (0.3-14 M1 m) reported by Rothlisberger (1967) and Rothlisberger and Vogtli (1967). Thus the surface resistivity is compatible with the thermal regime of an accumulation region of a temperate glacier.…”
Section: Resistivity Of Wormalo Ice Piedmontsupporting
Georesistivity soundings have been carried out at four sites in the Antarctic Peninsula. The objective of the work was to investigate the electrical behaviour of ice from an area where substantial melting occurs in summer and from contrasting thermal regimes. Electrical measurements made at three sites along a flow line within George VI Ice Shelf reveal that:(a)the resistivity of deep ice is similar to that of other Antarctic ice shelves,(b)the resistivity of the ice-shelf surface, which is affected by the percolation and refreezing of melt water, is similar to that of deep ice and hence the ice is polar in character.A compilation of published resistivities of deep ice from polar regions shows that the range of resistivities is very narrow (0.4 –2.0) x 105Ω m between –2 and – 29°C, irrespective of the physical setting and history of the ice. Typically, resistivity is within a factor of two of 80 kΩ m at –20° C with an activation energy of 0.22 eV. In contrast, the resistivity of surface ice at Wormald Ice Piedmont, where the ice is at 0°C throughout, is two orders of magnitude higher and falls at the lower end of the range of resistivities for temperate ice.
“…The resistivity of the surface ice layer (3.5 Mn m) is a factor of twenty higher than that of any surface layer on George VI Ice Shelf. It lies within the range of resistivities for the surface layers of temperate glaciers (0.3-14 M1 m) reported by Rothlisberger (1967) and Rothlisberger and Vogtli (1967). Thus the surface resistivity is compatible with the thermal regime of an accumulation region of a temperate glacier.…”
Section: Resistivity Of Wormalo Ice Piedmontsupporting
Georesistivity soundings have been carried out at four sites in the Antarctic Peninsula. The objective of the work was to investigate the electrical behaviour of ice from an area where substantial melting occurs in summer and from contrasting thermal regimes. Electrical measurements made at three sites along a flow line within George VI Ice Shelf reveal that:(a)the resistivity of deep ice is similar to that of other Antarctic ice shelves,(b)the resistivity of the ice-shelf surface, which is affected by the percolation and refreezing of melt water, is similar to that of deep ice and hence the ice is polar in character.A compilation of published resistivities of deep ice from polar regions shows that the range of resistivities is very narrow (0.4 –2.0) x 105Ω m between –2 and – 29°C, irrespective of the physical setting and history of the ice. Typically, resistivity is within a factor of two of 80 kΩ m at –20° C with an activation energy of 0.22 eV. In contrast, the resistivity of surface ice at Wormald Ice Piedmont, where the ice is at 0°C throughout, is two orders of magnitude higher and falls at the lower end of the range of resistivities for temperate ice.
“…Significantly, 10 8 -10 9 Ω m) is consistent with (though at the upper range of) previous, surface-based, estimates of the resistivity of temperate glacier ice (e.g. Röthlisberger, 1967; Röthlisberger and Vögtli, 1967). Fig.…”
ABSTRACT. Bor eh ole-based elec tri cal res isti vity sur veys have th e cap acity to enha n ce our understa nding of the structure of englaeial dra in age pathways in temperate ice. We summarize inter-borehole electrical resisti vity to m og raphy (ERT ) as currently used in hydrogeological inves tigation s and as ada pted fo r im aging eng lac ia l drainage. ERT co nn ections were successfull y m ad e fo r the first time in glacier ice, foll owing artificia l mineralization of borehole waters a t H aut Glacier d 'A roll a, Switzerl a nd. H ere, two typ es of electrical conn ection were m a de between boreh o les spaced up to 10 m a part and drill ed to depths of b etween 20 and 60 m. M ost tests indicated the presence o f resistively homogeneous ice with uniform bulk resistivities of ~ IO B -10 9 n m. However, ERT was also successfull y used to identify and characte ri ze a hydraulica ll y conducti ve eng lacial fr act ure tha t intersected two boreholes at a depth of ~ 13 m below th e glacier surface. The presence of thi s co nnecting void was suggested by drilling record s a nd ve rified by du a l boreholeimpulse testing. The reco nstructed tom ogra m for th ese b o reholes is cha rac terized by a backg round ice-resisti v ity field of ~ 10 9 n m that is disrupted at a depth of ~ 13 m by a sha rp, sub-hori zo ntal low-resistivity zone (~IO-l n m). Int er-borehole ERT, th erefore, has the cap acity to image b oth uniform a nd fractured temper a te glacier ice.
“…In this way, the problems of surface soundings on top of a highly insulating ice body (cf. Rothlisberger, 1967) are eliminated. Because of the high resistivity difference between the studied glacier bed material and the overlying glacier ice, the subglacial lithosphere can be considered as an electrical half-space.…”
Section: Principle S Of the Methodsmentioning
confidence: 99%
“…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.…”
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...
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