Inter-borehole electrical resistivity imaging of englacial drainage

Abstract

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.

Time-lapse imaging of subglacial drainage conditions using three-dimensional inversion of borehole electrical resistivity data

“…This implies that the current will be strongly concentrated in pore water within subglacial sediments, where they are present (Blake, 1992; Blake and Clarke, 1999). We expect this to be the case for our study area at Haut Glacier d’Arolla, where ice resistivity is known to be very large (~10 8 -10 9 Ωm; Hubbard and others, 1998) and the resistivity of the crystalline bedrock is also high (several thousand Ωm; e.g. Telford and others, 1990, p. 290).…”

“…During the second series, severe thunderstorms forced interruption of the resistivity surveys on several occasions (1700 h on day 232, and 0200 h and 0400–0600 h on day 233). All resistivity data were collected by manual switching with a Geopulse earth resistance meter (Campus Geophysical Instruments, UK), an instrument described in detail in Hubbard and others (1998).…”

Simultaneous time-lapse electrical resistivity inversion

“…(Binley et al, 1996;Kemna et al, 2002;Singha and Gorelick, 2006;Slater et al, 2000;Vanderborght et al, 2005). Surface based time-lapse electrical resistivity imaging (ERI) has been used to monitor saturation changes in order to gain understanding of natural hydrologic processes including: the monitoring of englacial drainage (Hubbard et al, 1998); inferring seasonal moisture content changes (Binley et al, 2002); characterizing seasonal recharge (Descloitres et al, 2008); imaging root zone moisture interactions (Jayawickreme et al, 2008); watershed characterization (Miller et al, 2008); and monitoring mountain slope hydrology (Cassiani et al, 2009). Some studies have monitored infiltration with time-lapse ERI and ERT eg.…”

Using borehole logging and electron backscatter diffraction to orient an ice core from Upper Fremont Glacier, Wyoming, USA

“…Geophysical logging instrumentation, which can include magnetic position, borehole inclination, gravity measurement, cross-hole electrical resistivity, echo sounding and optical imaging, has been used to provide detailed, oriented information on borehole geometry, englacial structure, drainage and deformation, and mass balance (Raymond, 1971; Jacobel and Raymond, 1984; Keller and others, 1995; Hubbard and others, 1998; Roberson and Hubbard, 2010). Both acoustic and optical measurements record magnetic north and produce a record of stratigraphy as a function of depth which can be used to produce an azimuthally oriented structure log.…”