Bed topography inferred from airborne radio-echo sounding of Columbia Glacier, Alaska

Abstract

The first airborne radio-echo sounding of a temperate glacier was performed in 1978 at Columbia Glacier, a large (1,100-squarekilometer), grounded, iceberg-calving glacier 38 kilometers west of Valdez, Alaska. The sounding system used a low frequency (about 1.5 megahertz) to overcome scatterings from water-filled voids in the ice, a short pulse, and an untuned receiver. Transverse and longitudinal profiles were flown over the lower 7 kilometers of the glacier. The received signal, the horizontal position of the airplane, and its altitude above the glacier surface were recorded by an FM tape recorder. For the data analysis, pictures of received energy from each flight profile were reconstructed from the taped data using an oscilloscope. Use of intersecting profiles allowed an internal consistency check to determine whether the correct bed reflection had been chosen. A three-dimensional geometric method of determining the envelope of the reflection lobes was developed for interpreting the data, instead of the differential method used by previous investigators. This analysis provided bedrock altitude determinations at every node of a 200-meter square grid. The probable error in the inferred bed altitudes was estimated to be 30 meters; the greatest depth was 370 meters below sea level.

Marginal Fluctuations of a Svalbard Surge-Type Tidewater Glacier, Blomstrandbreen, Since the Little Ice Age: A Record of Three Surges

“…2, part a, and 4, parts b and c). The associated increase in calving rate at greater depths (Brown et al, 1982;Pelto and Warren, 1991;Van der Veen, 1996;Vieli et al, 2001) is likely to have produced the complex pattern of ridges found in the center of the bay, indicating a more unstable grounding-line and, at times, the possible decoupling of the glacier from the bed. Luckman et al (2015) reported that some recent tidewater glacier fluctuations in Spitsbergen are linked to subsurface water temperature change (for which we have no data), but Blomstrandbreen appears to respond strongly to water-depth change and dynamic change associated with the surge cycle.…”

Tidewater calving

“…The largest uncertainty in the Columbia Glacier data set is associated with the basal elevations. In this study, elevations derived by Rasmussen (1989) are used for the main part of the fjord, while near the terminal moraine elevations derive from direct bathymetric soundings (Brown and others, 1986). These basal elevations may contain an important error and the poor correlation between calving rate and water depth could be attributed to uncertainties in the bed topography.…”

The directional dependence of the Ground Penetrating Radar response on the accumulation zones of temperate Alpine glaciers

“…GPR, in turn, is a logical successor to radio echo sounding (RES), as it has been called in the glaciological literature (e.g. Bjornsson 1986; Brown et al 1986 ; DeLisle et al 1989 ). The distinction between RES and GPR is discussed briefly by Arcone et al (1995 ).…”