The present work examines the possible near-snout overdeepening of a small outlet-valley glacier (Gígjökull, Ice-cap Eyjafjallajökull / Southern Iceland) and its influence on ice flow. The glacier is strongly determined by an icefall, which, together with an overdeepening, is thought to form a specific ‘icefall-overdeepening-regime’. The glacier can be considered as temperate (maritime climate).

The main objective of this work is to quantify the influence of a near-snout overdeepening on ice flow and to examine the general flow pattern considering various properties of the glacier which reflect glacier movement, or even exert an influence on it. For this reason, during two weeks of fieldwork in June/ July 1997 and July 1998, radio-echo sounding survey was carried out (2 Long-profiles; 8 Cross-profiles), and the movement of 4 strain nets and 4 transects was measured by using the EDM. Furthermore, the ice surface morphology was examined (icefall, crevasses, tephra-outcrop, debris distribution, meltwater channels, conduits, etc.) and stress and strain rates calculated.

RES revealed an ice thickness of about 120 m in the upper-section of the glacier terminus (just below the icefall) and of about 300 m in the bottom-section which had been expected to be overdeepened. The influence of the near-snout overdeepening on ice flow could be quantified, although bed rock topography and ice surface morphology did not correlate everywhere. Differences in flow velocities between near-snout areas and mid-glacier areas could be recorded. Although the glacier showed, in general, the expected flow pattern of a valley-glacier, some anomalies could be observed. Both the crevasse pattern and the tephra-outcrop revealed an unusually high compressive flow regime near the glacier snout, indicating a concave glacier bed. This was confirmed by calculated stress and strain rates.

Field observations exhibited an unusual drainage pattern: two supra-glacial meltwater channels ran laterally towards the ice margin (just below the icefall), fountains burst out of the ice, and closed-up conduits occurred frequently in this section of the glacier. Taken together, they could indicate a squeezing-out of meltwater towards the ice edge as the glacier flows into the overdeepening (i.e. as water pressure increases). The subglacial drainage pattern could therefore account for anomalies in glacier movement. Although the latter could not be examined in this work, a simplified concept for an icefall-overdeepening regime is suggested finally.

For further research it seems to be crucial to concentrate on the investigation of subglacial drainage networks in order to determine their influence on glacier movement.

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