LANDFORMS FROM A GLACIER SURGE ON A GRAVEL BED: ELISEBREEN, NW SPITSBERGEN

Retreat of Elisebreen, a glacier on Oscar II Land, NW Spitsbergen reveals a complex set of glacial landforms including drumlins, flutes, “till eskers”, crack-fill ridges, hummocky moraines and thrust moraines. Similar landform assemblages have been considered as glacier surge proxies (Evans and Rea, 1999). Accordingly, we suggest that Elisebreen experienced a surge in its sub-recent history.

The most conspicuous landforms are:

1. Closely spaced flutes up to 1 m high and 200 m long with initiating boulders at their proximal ends.

2. ”Till eskers”, i.e. sinuous-shaped ridges, typically 0.3-0.5 m high, occurring nearby the flutes and oriented generally ice-flow parallel. They are composed of till, similar to the till in the flutes.

3. Crack-fill ridges consisting of till, off-set consistently by 10-30° in relation to the ice movement. These ridges are typically 0.3-0.6 m high. They are superimposed on both flutes and “till eskers”.

4. A 30-35 m high thrust moraine with hummocks on the ice-proximal side.

Elisebreen rests on bedrock and, in its marginal part, on raised marine mud and gravel. Striated bedrock surfaces occasionally protrude through the <5-m-thick succession of unconsolidated sediments. It is suggested that this soft sediment triggered the surge due to its specific rheological behaviour in comparison with bedrock-overriding further up-glacier.

The sharp boundary between the basal till (which typically is less than 20 cm thick) and the undeformed sediments below suggests that fast ice motion was facilitated by deformation contained in the thin layer of till, and by basal sliding. Till mobility is evident from the presence of flutes and crack-fill ridges coupled with sediment deformation structures found therein.

Reference:

Evans, D.J.A., and Rea, B.R., 1999, Geomorphology and sedimentology of surging glaciers: a land-system approach: Annals of Glaciology, v. 28, p. 75-82.