The last glaciation in Caithness, Scotland: revised till stratigraphy and ice-flow paths indicate multiple ice flow phases

This paper reviews existing information on the last glaciation of Caithness and presents new evidence for additional till units and for long distance ice-flow paths based on till palynomorphs, indicator erratics and striae. Early, radial expansion of Northern Highland ice probably occurred at 31 – 29 ka. After ice withdrawal from the north coast, Moray Firth ice returned before a second withdrawal. Thereafter Moray Firth ice advanced to limits close to the Atlantic shelf edge between 21 and 18 ka. Deglaciation of hill summits was completed by 18.4 – 17.8 ka but the low ground south of Wick only became ice free after 16.5 ka. Recognition of these multiple ice-flow events is consistent with the dynamic behaviour of the last ice sheet exhibited in mathematical simulations. The event sequence differs, however, from nineteenth century and recent two-stage flow set reconstructions as each main flow set is shown to represent multiple events following similar paths but under different ice sheet configurations. Various configurations allow ice to flow northwards across Caithness and so remove any requirement for the Fennoscandian Ice Sheet to directly block and divert the outflow of ice from the Moray Firth during the last glaciation.