The ‘Captured Ice Shelf’ Hypothesis and its Applicability to the Weichselian Glaciation

ABSTRACT

The early and late stages of the Weichselian glaciation of the Baltic Sea proper and the Baltic countries is tentatively suggested as having been by means of a thin ice with very low basal friction, to a great extent floating on a number of water-filled cavities. The terms 'captured ice shelf and ‘captured lake’ are introduced, suggesting that a floating ice is the norm, rather than an exception, in this concept. The captured ice shelf-hypothesis states, that a moving floating ice may, if and when the entire perimeter of the water body is reached by this floating ice (or ‘captured ice shelf’), develop an ‘ice rim’ that acts as a hydrostatic seal, so that the water under the captured ice shelf cannot get out (it is a ‘captured lake’). Meltwater inflow to the captured lake will lift the captured ice shelf, until the base of the latter reaches the level of the threshold, at which time the water will escape in a jökulhlaup. The water can escape to the next captured lake in a chain, or to the extra-marginal environment. Tunnel valleys and mid-sea channels with dead ends are suggested to be the product of these kinds of jökulhlaups.