Ross suggests that the last ice sheet over the Shetland Islands was at its maximum perhaps 150 kilometres wide and over 1000 metres thick. It stretched from north-east to south-west along the western edge of the continental shelf. Much of the ablation during deglaciation was due to ice calving into a rising sea and the position of the icecap relative to bathymetry exerted a strong influence on the movement of the ice shed. Rapid deglaciation in the west and north-west moved the ice shed to the east of the island chain and, although it is not possible to wholly resolve the issue, evidence previously attributed to Scandinavian glaciation could have resulted from the shift. Deglaciation commenced on the margins of the icecap in a clockwise fashion. Following early western deglaciation, the North, north-east, East, south-east and south-west margins began deteriorating significantly as sea level rose. Preliminary dates suggest deglaciation was under way before 17,000 years BP to the north and 13,000 years BP to the east. The margin of the ice cap appears to have become wholly terrestrial at about the -100 m bathymetric contour, due to a stabilisation in relative sea level rise or a step-change in the bathymetry at -82 m OD around parts of the island. By that stage, the Shetland Islands and surrounding topography were exerting considerable influence in the containment of ice flow. Parts of Shetland may have been ice free up by 13,000 years BP but the date is uncertain. There is evidence of later glaciation on the Ronas Hill plateau and in valleys on other parts of the islands but these events are not dated.

Ross (1996) model of the last glacial maximum around Shetland