Papers by Hermann Engelhardt
Videos of Basal Ice in Boreholes on Kamb Ice Stream in West Antarctica
Basal hydraulic conditions of Ice Stream B
Fifteen boreholes have been drilled to the base of Ice Stream B in the vicinity of UpB Camp. The ... more Fifteen boreholes have been drilled to the base of Ice Stream B in the vicinity of UpB Camp. The boreholes are spread over an area of about 500 x 1000 m. Several till cores were retrieved from the bottom of the 1000-m-deep holes. Laboratory tests using a simple shear box revealed a yield strength of basal till of 2 kPa. This agrees well with in-situ measurements using a shear vane. Since the average basal shear stress of Ice Stream B with a surface slope of 0.1 degree is about 20 kPa, the ice stream cannot be supported by till that weak. Additional support for this conclusion comes from the basal water pressure that has been measured in all boreholes as soon as the hot water drill reached bottom. In several boreholes, the water pressure has been continuously monitored; in two of them, over several years. The water pressure varies but stays within 1 bar of flotation where ice overburden pressure and water pressure are equal. The ratio of water and overburden pressure lies between 0.9...
Journal of Geophysical Research, 1994
Measurements of glacier flow velocity and basal water pressure at two sites on Columbia Glacier, ... more Measurements of glacier flow velocity and basal water pressure at two sites on Columbia Glacier, Alaska, are combined with meteorological and hydrologic data to provide an observational basis for assessing the role of water storage and basal water pressure in the rapid movement of this large glacier. During the period from July 5 to August 31, 1987, coordinated observations were made of glacier surface motion and of water level in five boreholes drilled to (or in one case near to) the glacier bed at two sites, 5 and 12 km from the terminus. Glacier velocities increased downglacier in this reach from about 4 m d-• to about 7 m d-•. Three types of time variation in velocity and other variables were revealed: (1) Diurnal fluctuation in water input/output, borehole water level, and ice velocity (fluctuation amplitude 5 to 8%); (2) Speed-up events in glacier motion (15-30% speed up), lasting about 3 days, and occurring at times of enhanced input of water, in some cases from rain and in others from ice ablation enhanced by strong, warm winds; (3) "Extra-slowdown" events, in which, after a speed-up event, the ice velocity decreased in about 3 days to a level consistently lower than that prior to the speed-up event. All of the time variations in velocity were due, directly or indirectly, to variations in water input to the glacier. The role of basal water in causing the observed glacier motions is interpreted by Kamb et al. (this issue).
Environmental Microbiology, 2009
Subglacial environments, particularly those that lie beneath polar ice sheets, are beginning to b... more Subglacial environments, particularly those that lie beneath polar ice sheets, are beginning to be recognized as an important part of Earth's biosphere. However, except for indirect indications of microbial assemblages in subglacial Lake Vostok, Antarctica, no sub-ice sheet environments have been shown to support microbial ecosystems. Here we report 16S rRNA gene and isolate diversity in sediments collected from beneath the Kamb Ice Stream, West Antarctic Ice Sheet and stored for 15 months at 4°C. This is the first report of microbes in samples from the sediment environment beneath the Antarctic Ice Sheet. The cells were abundant (~10 7 cells g-1) but displayed low diversity (only five phylotypes), likely as a result of enrichment during storage. Isolates were cold tolerant and the 16S rRNA gene diversity was a simplified version of that found in subglacial alpine and Arctic sediments and water. Although in situ cell abundance and the extent of wet sediments beneath the Antarctic ice sheet can only be roughly extrapolated on the basis of this sample, it is clear that the subglacial ecosystem contains a significant and previously unrecognized pool of microbial cells and associated organic carbon that could potentially have significant implications for global geochemical processes.
Geophysical Research Letters, 2005
Borehole observations from the base of the West-Antarctic Ice Sheet (WAIS) reveal the presence of... more Borehole observations from the base of the West-Antarctic Ice Sheet (WAIS) reveal the presence of a 10 to 15 m thick accretionary basal ice layer in the upstream area of Kamb Ice Stream (KIS). This ice layer has formed over a time of several thousand years by freeze-on of subglacial water to the ice base and has recorded during this time basal conditions upstream of its current location. Analysis of samples and videos sequences from boreholes drilled to the bottom of KIS confirms that KIS-stoppage was due to basal freeze-on and that relubrication of the ice stream is well underway. These results further suggest that ice stream cyclicity may be shorter than expected (1000s of years) and that a restart of KIS may be imminent within decades to centuries.
Space-charge limited proton currents in ice
Physics Letters
Journal of Glaciology
Periods of dramatically accelerated motion, in which the flow velocity increases suddenly from ab... more Periods of dramatically accelerated motion, in which the flow velocity increases suddenly from about 55 cm/d to a peak of 100–300cm/d and then decreases gradually over the course of a day, occurred repeatedly during June and July 1978–81 in Variegated Glacier (Alaska), a surging-type glacier that surged in 1982–83. These “mini-surges” appear to be related mechanistically to the main surge. The flow-velocity peak propagates down-glacier as a wave at a speed of about 0.3 km/h, over a reach of about 6 km in length. It is accompanied by a propagating pressure wave in the basal water system of the glacier, in which, after a preliminary drop, the pressure rises rapidly to a level greater than the ice-overburden pressure at the glacier bed, and then drops gradually over a period of 1–2 d, usually reaching a new low for the summer. The peak velocity is accompanied by a peak of high seismic activity due to widespread fresh crevassing. It is also accompanied by a rapid uplift of the glacier s...
Journal of Glaciology
Bore-hole photography demonstrates that the glacier bed was reached by cable-tool drilling in fiv... more Bore-hole photography demonstrates that the glacier bed was reached by cable-tool drilling in five bore holes in Blue Glacier, Washington. Basal sliding velocities measured by bore-hole photography, and confirmed by inclinometry, range from 0.3 to 3.0 cm/d and average 1.0 cm/d, much less than half the surface velocity of 15 cm/d. Sliding directions deviate up to 30° from the surface flow direction. Marked lateral and time variations in sliding velocity occur. The glacier bed consists of bedrock overlain by a ≈ 10 cm layer of active subsole drift, which intervenes between bedrock and ice sole and is actively involved in the sliding process. It forms a mechanically and visibly distinct layer, partially to completely ice-free, beneath the zone of debris-laden ice at the base of the glacier. Internal motions in the subsole drift include rolling of clasts caught between bedrock and moving ice. The largest sliding velocities occur in places where a basal gap, of width up to a few centimet...
Journal of Glaciology, 1978
Ice IV, a wholly metastable ice phase, has a structure based on a framework of tetrahedrally hydr... more Ice IV, a wholly metastable ice phase, has a structure based on a framework of tetrahedrally hydrogen-bonded water molecules in a rhombohedral unit cell. The structure involves two non-equivalent types of water molecules and four non-equivalent types of hydrogen bonds. A novel structural feature is a hydrogen bond that passes through the center of a 6-ring of water molecules and links non-adjacent structural layers. The bond network is proton-disordered, even after quenching.
Zur protonischen Leitf�higkeit von Eis-Einkristallen bei tiefen Temperaturen und hohen Feldst�rken
Eur Phys J B, 1966
Basal mechanics of Ice Stream B
Borehole evidence for a thick layer of basal ice in the central Ronne Ice Shelf
Epic3nature 327 Pp 318 319 Issn 0028 0836, May 28, 1987
The Ronne Ice Shelf, floating between Berkner Island and the Antarctic peninsula, is the biggest ... more The Ronne Ice Shelf, floating between Berkner Island and the Antarctic peninsula, is the biggest ice shelf in Antarctica. It drains an estimated 1.2 × 106 km2 of the Antarctic ice sheet, much of it resting on bedrock below sea level. Consequently, the balance and dynamics of this ice shelf is of importance to Antarctic glaciology, especially with regard to the integration of this part of the cryo-sphere into the global processes that control the climate of the Earth. Extensive radio-echo sounding (RES) by Robin and others revealed reflections in the central part of the Ronne Ice Shelf at the relatively shallow depth of 100-200 m below surface1. The interpretation of these echoes, which varied in strength, was ambiguous, and the possibility of internal reflecting horizons was thoroughly discussed. But after surface elevation measurements by radar altimeter from drifting balloons appeared to fit the presence of thin ice, it was decided to base a thickness map of the Ronne Ice Shelf on these RES echoes1-4. We now present direct observational evidence from boreholes that the total ice thickness is much greater than mapped, and that the shallow RES reflections therefore do come from internal horizons.
A Solid. (Book Reviews: Physics of Ice. Proceedings of an international symposium, Munich, Sept. 1968)
Science, Jul 1, 1970
The Mars Polar Caps are highly interesting features of Mars and have received much recent attenti... more The Mars Polar Caps are highly interesting features of Mars and have received much recent attention with new and exciting data on morphology, basal units, and layered outcroppings. We have examined the climatological, glaciological, and geological issues associated with a subsurface exploration of the Mars North Polar Cap and have determined that a finescale optical examination of ice in a
MTS/IEEE Oceans 2001. An Ocean Odyssey. Conference Proceedings (IEEE Cat. No.01CH37295), 2000
Results are presented of a preliminary analysis of ice cores obtained by hot water drilling at Si... more Results are presented of a preliminary analysis of ice cores obtained by hot water drilling at Siple Dome, Antarctica. Cores were retrieved from pre-selected depths on both the summit and flank of the Dome. These included all cores obtained within 15 m of the bed at the summit site and to within a meter or two of the bed at the flank site. Basal ice at the summit is frozen to the bed at -l.3 °C, approximately 0.5 °C below the pressure melting point. Brittle ice was first encountered at 400 m and continued to the bottom of the ice sheet. Fracturing was most severe around 500-600 m. This fracturing occurred soon after cores were retrieved. However, the mechanical condition of the ice appeared to stabilize within a few days of core recovery. The rapidity of relaxation is attributed mainly to thermal effects associated with the hot water drilling process and partly to the rapidly increasing temperatures and the highly recrystallized nature of the ice below 600 m. Volume expansion of the ice associated with this relaxation process ranged from 0.3 % at around 300 m to nearly 3 % in the deepest ice. Air bubbles were observed at all depths; a decrease in the sizes and concentrations of bubbles in the deepest ice is attributed to gas hydrate formation. An abrupt increase in the size of crystals Physics of Ice Core Records Edited by T. Hondoh
Journal of Geophysical Research, 1993
An unphumed, but unique, experiment has given an in situ measurement of the strength of deforming... more An unphumed, but unique, experiment has given an in situ measurement of the strength of deforming subglacial till under the central region of a major valley glacier. We report on both planned and unplanned borehole investigations of the subglacial shear zone of Columbia Glacier, southeast Alaska. Basal samples, coring and down-hole water samples show that the fiord-filling lower reach of the •acier is underlain by a thin, ~ 7-cm, veneer of rock debris. Fluidized debris intruded at least a meter up the borehole. At a higher site, 13 km from the terminus and above the fiord, probing, samples, and the bending of a drill stem, which was stuck in the basal zone for 5 days, showed that the basal till layer was ~ 65 crn thick. Horizontal velocity of the till decreased monotonically downward from the ice/till interface. Till at the interface moved with the ice velocity. Plastic deformation of the drill stem gave an estimate of the strength of the basal till, which is normally described as a viscoplastic materiM. If the till is assumed to be either perfectly plastic or Newtonian viscous, then the strengths are as follows; the plastic yield strength of the till was 5.5 x!03 Pa (0.055 bar) with an upper bound of 1.3 x104 Pa (0.13 bar), while the nominal viscosity was of the order of 2x108 Pas (2x109 poise), with an upper bound of 5x108 Pas. In neither case is the till "strength" enough to supply the bulk basal shear stress to resist the glacier flow. Columbia Glacier is a large (1100 km 2) tidewater glacier. The terminus occupies a fiord about 5 km wide, which extends over 15 km into the Chugach Mountains and has a maximum depth of some 400 m below sealevel. Approximately 12 km above the calving terminus the fiord narrows before widening into the extensive upper region of the glacier. An icefall forms at this constriction, and ice speed doubles from the upper, slower, region to the fast moving fiord tongue. The chaotic crevassing created in the constriction does not smooth out below the icefall, but persists into the low angie slope (~ 1.5 degree) of the terminus region. Previous work [Krimmet, 1987; Walters, 1989; Meier et al., 1987] has shown correlations between the spee d of the ice in the terminus region and both the water inputs to the glacier and the water pressure (tidal) on the snout. Current work by Fahnestock [1990] correlates ice speed with subglacial water volume. The terminus has retreated in the last 6 years as a result of increased calving [Meier et al., 1987; Krimmel, 1987]. FIELD STUDIES Two hot-water drilling sites were established on the glacier, and holes were drilled to the bed to measure basal water pressures, reported elsewhere [Engelhardt et al., 1987]. The upper site was located approximately 13 km from the terminus, in the upper reaches of the icefall. The lower site, 6 km from the terminus, was located on the highly crevassed glacier surface below the icefall. The drill sites lay approximately on a single flow line, as indicated by proximity to a medial moraine traced with aerial photography. At each site, samplers were lowered to the bed, and investigation of the basal material was undertaken. Lower Drill Site The lower drill site was located on an ice serac in the crevassed lower reach of the glacier, some 160 m above sealevel and ~ 520 m above the glacier bed. Ice surface speed was high, about 7.5 m per day [Meier et al., 1987]. Two holes were drilled ~5 m apart using a hot-water 'drill. One hole was reamed to 7.5-cm diameter and was used to lower instruments to the bed. A sliding hammer, which could be lowered to the bed on a steel wire, provided initial indications of the physical character of the basal zone. The hammer consisted of a 20 kg weight 837 838 HUMPHREY •'T •a•.: BED OF COLUMBIA GLACIER that slides on a 1.5 m long, 1.2-cm diameter steel shaft. The hammer could be repeatedly raised and dropped ~ 1 m, using the steel support cable. Either a 1.2-cm diameter mild-steel point (penetrometer poin0 or a coring tube (5-cm diameter), could be attached to the hammer shaft and driven into the base of the borehole. The barrel of the sliding hammer could be made watertigl'/t, and when the hammer and attached probe were lifted from the bed, with the hammer slide fully extended, a sample of fluid in the borehole at a level about 2 m above the bed was obtained.
Uploads
Papers by Hermann Engelhardt