Surging ice and break-down of an ice dome – a deglaciation model for the Gulf of Bothnia

Abstract

Based on studies of striae in the Kvarken area in the northern part of the Baltic basin, and re-interpretation of stratigraphic sequences earlier interpreted as evidence of a readvance of the ice margin in the Gulf of Bothnia a model for the deglaciation of the Gulf is proposed. The model implies quick break-up of the ice due to areal thinning of an ice lobe in the Gulf and change from cold-based to warm-based ice. Wide calving bays were formed close to and into the centre of the ice in the northern part of the Gulf. The change of balance caused sudden collapses in the centre followed by surges upon the warming base of soft ductile sediments. The effect was a westward shift of the ice centre from the Gulf area towards the mountain range. The ice sheet changed from a thick one with a subaquatic margin into a thin, terrestrial one, thus becoming more sensitive to the rising temperature at the end of the Weichselian glaciation.

Key Words:

• Deglaciation
• Gulf of Bothnia
• surges
• ice domes
• striae