JournaL of CLacioLogy , Vol. 30, No. 106, 1984 ELECTRICAL RESISTIVITY SOUNDINGS OF GLACIER BEDS: A TEST STUDY ON GRUBENGLETSCHER, WALLIS, SWISS ALPS By WILFRIED HAEBERLI (Versuchsan stalt fur Wasserbau , Hydrologie und Glazi ologi e, E.T.H. Zuri ch, CH-8093 Zurich , Switzerland ) and WER NER FIS CH ( Im Wi ese ngrund 13 , CH-8907 Wettswil , Zurich, Switzerland) ABSTRA CT . El ec tri cal res isti vity so undin g, using el ec trodes whi ch are lo w- ered dir ec tl y to the ice- rock inte rf ace in bore holes, is proposed as a tec h- nique for stud ying the exact pos ition of glacier beds, as well as their lithological char ac te ri stics. A test study is described on G rubengletscher, a partially cold Alpin e gl acier in Swit ze rl a nd. Res ul ts of so undin gs along a 400 m long pro fil e indicate that previous depth determina ti ons, based on radio echo-soundin gs, were in ge neral acc ura te to within less than 5 0/ 0 of the actual ice thickness. Th e resu lts also show that the glacier rests on no n- consolid a ted sedimen ts of considerable thickn ess. Th e proposed method could add substa nti al inf o rm a ti on abo ut glac ier sliding and gla cie r erosion, if appli ed alongside conve ntional deep drilling proj ec ts. RESUME. So ndages de risistivili eleclrique dans le lit glaciai r e: une mes ure !u t au gla cier de Cruhen, Va lais, Alpes su isses. Des so nd ages de c lcc triqu e a I'aide d'eiec lrodes in sta ll ees cl ans d es fo rages directement it l' int e rf ace glace- roc he, so nt pro poses co mme tec hniqu e pour determin er la position exac le du lit g lacia ire a in si que ses caracte ri stiques litholog iqu es. On decrit une mesure test re ali see au glacier de Grub en, glac ier pa rti elleme nl fr oid des Alpes sui sses. Les resultats des mes ures fa it es sur un profil de 400 m de long mo ntrent que les epaisseurs de glace es tim es a ll parava nt par ra di o-echo I NTRODUCTI ON The beds of existing glaciers are characterized by a wide variety of morphological and lithological conditions . These beds may be rough or smooth depend- ing 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, know- ledge 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 pro- 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 al- ready existing rock galleries upwards, to probe the glaCier bed. Scientific studies have to try less ex- pensive 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 resist- ivity soundings of glacier beds . sond age ne d eviaient en ge neral que de 5 0 / 0 de la v al e ur exaCle. D 'a utre part , on a trouve que la langue du glacier se trouve s ur des sediments non consolides d'epaisse ur consid era bl e. En a ppliquant la methode proposee lo rs de ca mpag ne de fo rage conven ti onell e, on pourrait obte nir d' impo n a ntes inf orma ti ons suppl ementaires sur le glissement et l'erosio n d es g lac ier s. Z US AMMENFASSUNG. Eleklrische Widerstan dssondieru n gen am Glelscherbell : eine T eslmessung am Crube n gietscher , Wallis, Schweizer A lpen. Elektri sc he Wi de r- stand ssondierungen mit El e ktroden, di e in Bo hrl oc hern direkt an der Eis unt e rg re nze in stalliert we rden, wcrd en fU r di e U nt ersuchung der ge- nau en Lage und der litholog ischen Charakteri st ik von G letscherbetten vor- geschl age n. Eine Testmess un g am Grubengletscher, ein em teil weise kalten Gl etscher der Schweiz er Alp en, wird beschrieben. Ergebni sse ein er Son- di e run g a uf ein em 400 m la nge n Profil ze ige n, dass mit Radioecholot zuvor bes timmt e Eisti efen im a ll ge meinen urn weni ge r als 5% vo n der effektive n Eistiefe abweichen. Di e Gletscherzunge li egt a ufun verf es ti g ten Sedi me nt en von be tr iichtlicher Miichtigkeit. Di e vo rgeschl age ne Methode kii nl1t e im Ra hmen von konve ntione ll en Ti efb ohrprojekten wichtige In fo rmat io n uber G letschergleite n und Gletschererosion li efe rn . PRINCIPLE S OF THE METHOD The method is a combination of two well-known techniques: (thermal) drilling in ice and electrical resistivity soundings of sub-surface materials. Com- bining the two techniques helps to overcome the prob- lems and limitations of interpreting results whi ch occur when the techniques are applied separately. Standard resistivity techniques are applied directly at the glacier bed by lowering the electrodes down drill holes to the ice-rock interface . Such electri- cal measurements can help to define the exact position of the glacier bed, and, moreover, they provide in- formation about lithological changes in a horizontal direction (between the bore holes) as well as in a vertical direction, down into the subglacial material. Thermal drilling from the ice surface to the glac- ier bed often encounters the problem that increased amounts of rock particles included in the basal layer of glaciers gradually lower the drilling speed. Hot- water jets may finally wash out these inclusions and even penetrate into glacier bed sediments if they are fine-grained, whereas electrothermal drills will, in many cases, not completely reach the glacier bed. (Hot-water drilling has in this respect an advantage over electrothermal drilling.) In either case it is difficult to determine from observed drilling rates the exact position of the glacier bed . A simple electrical measurement, however, indicates whether and where a drill has reached the glacier bed. The array of the electrical measurement is shown in Fig- ure la. The measurement is based on the fact that the specific electrical resistivity of temperate or nearly temperate glacier ice is usually much higher (p i > 10 7 n m) than that of the underlyi ng rock material (p r« 10 6 n m). A fixed el ectrode (FE) is grounded outside the glacier margin, usually in a pond or another water body to improve surface contact. A second ele ctrode, the bore-hole electrode (BE), is 373 https://www.cambridge.org/core/terms. https://doi.org/10.3189/S0022143000006250 Downloaded from https://www.cambridge.org/core. IP address: 168.151.145.126, on 24 Sep 2017 at 09:36:50, subject to the Cambridge Core terms of use, available at