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Time-Dependent Intraglacier Structures

Published online by Cambridge University Press:  30 January 2017

R. H. Goodman
R. H. Goodman*
Affiliation:
Inland Waters Branch, Canada Department of the Environment, Calgary, Alberta, Canada
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Abstract

Using time-domain pulsed radar, the intrastructure of a typical temperate glacier has been studied. Certain features have exhibited a rapid change in structure, and cannot be explained by density or ice characteristics of a stable nature. It is believed these time-dependent structures are related to the internal water system for glaciers.

A l’aide du radar pour sondage-temps, on a pu étudier la structure interne d’un glacier tempéré typique. Certains traits caractéristiques ont mis en évidence un changement rapide de structure, et ne peuvent pas être expliqués ni par la densité ni par des caractéristiques stables de la glace. On croit que ces structures influencées par le temps sont liées au système aqueux interne d’un glacier.

Zusammenfassung

Zusammenfassung

Unter Verwendung eines im Zeit-Bereich gepulsten Radars wurde die Innenstruktur eines typischen temperierten Gletschers untersucht. Bestimmte Erscheinungen zeigten eine rasche Strukturveränderung; sie können nicht auf Grund der Dichte oder aus Eiseigenschaften stabiler Natur erklärt werden. Es wird angenommen, dass solche zeitabhängige Strukturen mit dem inneren Wassersystem des Gletschers in Zusammenhang stehen.

Information

Type
Short Notes
Information
Journal of Glaciology , Volume 12 , Issue 66 , 1973, pp. 512 - 513
Copyright
Copyright © International Glaciological Society 1973

During experiments using radio depth measurements at 620 MHz (Reference Goodman and GudmandsenGoodman, 1970) on Athabasca Glacier in the Canadian Rockies, several intraglacial reflections were noted. A sounding was obtained in the same location, under the same experimental conditions (except for weather), with a time lapse of nearly 1 month (late August to late September). The results of the two sets of data are shown in Figures 1 and 2. It is clear that the bottom remains unchanged, but the structure of the intraglacial layers at the right of the figures has changed considerably. Reference Robin, Robin, Evans and BaileyRobin and others (1969), using a 35 MHz system in Greenland, noticed intraglacier reflections which were attributed to changes in ice density. Russian workers (Reference Rudakov and LuchininovRudakov and Luchininov, 1969) have observed similar reflections in a temperate glacier and assigned these to water lenses, cracks and the existence of clear ice. The rapid change in reflected layers observed on Athabasca Glacier eliminates the above explanations for the cause of the rapid time-varying intraglacial reflections.

Fig. 1.Data tape taken 22 August. Weather sunny, no recent rain; the various symbols (★, ■, ●, ▲) represent returns of similar intensity and time delay.

Fig. 2.Data tape taken 21 September. Snow and blowing snow; about 60 cm snow on ice.

There are at least two possible explanations. The reflections could be due to water layers forming and vanishing within the ice. The region, where these layers were observed, was near a large crevasse field. An alternative explanation is that these layers represent glide planes which cause an alignment of the crystal axes. This effect has been discussed by Reference Luchininov and RudakovLuchininov and Rudakov (1971). It is difficult, however, to see how these planes could form and disappear so rapidly, since the crystal size must be in the order of a wavelength (50 cm).

The calculations of Reference Smith and EvansSmith and Evans (1972) are based on a multi-layer model of water admixed with ice. Using such a structure, it is predicted that a glacier greatly attenuates signals at frequencies above 500 MHz. Experimentally, this has not been observed except under conditions of recent precipitation. If such a multi-layer structure exists, it is rapidly drained leaving only a few well-defined features.

Experiments are in progress to obtain information on the diurnal, annual and spatial behavior of the intraglacier structure.

References

Goodman, R. H. 1970. Radio echo sounding on temperate glaciers: a Canadian view. (In Gudmandsen, P., ed. Proceedings of the international meeting on radioglaciology. Lyngby, May 1970. Lyngby, Technical University of Denmark, Laboratory of Electromagnetic Theory, p. 135–46.)Google Scholar
Luchininov, V. S., and Rudakov, V. N. 1971. K voprosu ob izuchenii anizotropii snezhno-ledovogo pokrova metodami introskopii [On the question of the anisotropic study of snow-ice blankets by introscope methods]. Zhurnal Tekknicheskoy Fiziki, Tom 41, Vyp. 1, p. 212–15. [English translation: Soviet Physics. Technical Physics, Vol. 16, No. 1, 1971, p. 162–64.]Google Scholar
Robin, G. de Q., and others. 1969. Interpretation of radio echo sounding in polar ice sheets, by Robin, G. de Q., Evans, S. and Bailey, J. T.. Philosophical Transactions of the Royal Society of London, Ser. A, Vol. 265, No. 1166, p. 437–505.Google Scholar
Rudakov, V. N., and Luchininov, V. S. 1969. Ledovaniye neodnorodnostey v lednikakh metodami radiointroskopii [Radio sounding of glacier inhomogeneities]. Zhurnal Tekhnicheskoy Fiziki, Tom 39, Vyp. 6, p. 1001–06. [English translation: Soviet Physics. Technical Physics, Vol. 14, No. 6, 1969, p. 751–55.]Google Scholar
Smith, B. M. E., and Evans, S. 1972. Radio echo sounding: absorption and scattering by water inclusion and ice lenses. Journal of Glaciology, Vol. 11, No. 61, p. 133–46.Google Scholar
Figure 0

Fig. 1.Data tape taken 22 August. Weather sunny, no recent rain; the various symbols (★, ■, ●, ▲) represent returns of similar intensity and time delay.

Figure 1

Fig. 2.Data tape taken 21 September. Snow and blowing snow; about 60 cm snow on ice.