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Drainage-Basin Characteristics of Nordaustlandet Ice Caps, Svalbard

  • Julian A. Dowdeswell (a1)

Abstract

Recent mapping of ice-surface and bedrock topography from airborne radio-echo sounding has shown that the ice caps of Nordaustlandet, Svalbard, are divided into a series of well-defined drainage basins. Three lines of evidence indicate that several distinctive modes of ice-flow regime characterize these basins: (1) comparison between observed and theoretical ice-surface profiles; (2) analysis of driving stresses; and (3) observations of ice-surface features on satellite imagery and air photographs. The drainage basins are inferred to behave in the following ways. First, basins with low driving stresses and surface profiles, some of them clearly stagnant, are associated with the quiescent phase between glacier surges. Secondly, the ice streams draining southern Vestfonna have low surface profiles, relatively low driving stresses, and marked shear zones at their margins. They are interpreted to be flowing continuously at a relatively faster rate than the ridges between them. Basal melting, perhaps combined with substrate deformation, is probably responsible for the regime of these glaciers. Thirdly, the remaining basins studied on Nordaustlandet have relatively high marginal driving stresses and high surface profiles. They are interpreted to be frozen to their beds, at least near their margins. Some of these basins may also surge, particularly those where a part of the basin is below sea-level, and therefore is probably underlain by considerable thicknesses of deformable sediments.

Résumé

Des cartes récentes de la surface et du lit rocheux à partir de sondages radar aérien ont montré que les calottes glaciaires de la Nordaustlandet, sont divisées en séries de bassins d’écoulement bien définis. Trois critéres indiquent que plusieurs types de régime d’écoulement caractérisent ces bassins: (1) comparaison entre profils superficiels observés et théoriques; (2) analyse de la cission au contact du lit; (3) observation des caractéristiques superficiels sur l’imagerie satellitaire et les photographies aériennes. Les différents bassins d’écoulement sont supposés présenter les comportements suivants. Il y a tout d’abord des bassins, où la cission basale est faible et les profils longitudinaux de la surface abaissés, certains d’entre eux, nettement stagnant, sont associes aux phases quiescentes entre deux surges. En second lieu, les courants de glace drainant le Vestfonna méridional ont des profils de surface bas, des contraintes relativement basses et des zones de cisaillement marqué sur les bords. Ces courants sont supposés couler continuellement à une vitesse plus grande que leurs limites. La fonte basale, peut être combinée avec la déformation du substratum, est probablement responsable du régime de ces glaciers. Troisiémement les autres bassins étudiés sur le Nordaustlandet montrent de relativement fortes contraintes marginales et des profils de surface élevés. Ils sont interprétés comme étant gelés contre leurs lits, du moins prés des bords. Certains de ces courants peuvent aussi “surger”, spécialement ceux dont une partie se trouve en dessous du niveau de la mer, et qui reposent sur des épaisseurs considérables de sédiments déformables.

Zusammenfassung

Die neuerliche Kartierung der Eisoberfläche und des Felsuntergrundes aus Echolotungen mit Flugradar hat gezeigt, dass die Eiskappen von Nordaustlandet in Spitzbergen in eine Reihe wohlabgegrenzter Abflussbecken unterteilt sind. Drei Beweisverfahren deuten darauf hin, dans einige unterschiedliche Arten des Fliessverhaltens des Eises diese Becken charakterisieren: (1) Vergleich zwischen beobachteten und theoretischen Profilen der Eisoberfläche; (2) Analyse der Treibdrucke; (3) Beobachtungen von Erscheinungen an der Eisoberfläche in Satelliten- und Luftbildern. Über das Verfhalten der Abflussbecken lässt sich folgendes aussagen: 1. Becken mit niedrigen Treibdrucken und Oberflächenprofilen, einige davon sichtlich stagnierend, sind mit der Ruhephase zwischen GletscherausbrÜchen verknÜpft. 2. Die aus Süd-Vestfonna abfliessenden Eisstrŏme haben niedrige Oberflächenprofile, relativ hohe Treibdrucke und markante Scherzonen an ihren Rändern; sie werden als kontinuierliche Ströme mit einer relativ höheren Geschwindigkeit als die der dazwischenliegenden Rücken interpretiert. Schmelzen am Untergrund, vielleicht verbunden mit Deformation des Substrats, ist vermutlich für das Verhalten dieser Gletscher verantwortlich. 3. Die übrigen, auf Nordaustlandet untersuchten Becken weisen relativ hohe randliche Treibdrucke und hohe Oberflächenprofile auf. Es wird angenommen, dans sie am Untergrund festgefroren sind, zumindest in Randnähe. Einige dieser Becken mŏgen auch ausbrechen, namentlich solche, wo ein Teil des Beckens unter dem Meeresspiegel liegt und deshalb vermutlich von deformierbaren Sedimenten erheblicher Mächtigkeit unterlagert wird.

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References

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