Scottish Landform Example: subaqueous moraines around the Summer Isles and in the approaches to Loch Broom (Wester Ross Marine Protected Area)

Abstract

The seabed landscape around the Summer Isles (NW Scotland) hosts classic examples of subaqueous moraines formed at a Late Pleistocene tidewater ice-sheet margin. This suite of moraines, now within the Wester Ross Marine Protected Area, records oscillatory retreat of the grounding line of (one or more) large outlet glaciers receding from the open waters of the Minch into the fjords of Loch Broom and Little Loch Broom at the end of the last (Weichselian / Devensian) glaciation. The moraines, probably the best-studied examples in UK waters, formed by a combination of pushing, dumping and/or squeezing of sediment at the grounded tidewater glacier front. Their absence in some basins suggests that the glacier front was un-grounded (partially floating) in areas of deeper water. Some of these seabed moraines can be connected to ice-sheet moraines onshore, assigned to the Wester Ross Readvance, and dated to ca. 15.5 ka BP. Geomorphological evidence strongly suggests that the whole sequence represents relatively slow and punctuated ice-front retreat over a period of decades to centuries. Continued protection of these rare and distinctive seabed moraines is important, both on geological and ecological grounds. The moraines represent the first underwater Scottish Landform Example in this long-running series.