Retreat dynamics of Younger Dryas glaciers in the far NW Scottish Highlands reconstructed from moraine sequences

Abstract

Knowledge about moraine sequences produced by former glaciers can reveal much about the interaction between glaciers and palaeoclimate. In the far NW Highlands of Scotland, detailed records of deglaciation during the Younger Dryas (Loch Lomond Stadial) are preserved in sequences of ‘hummocky moraines’, consisting of arcuate chains of ridges and mounds, marking successive palaeo‐ice fronts. Reconstructed ice‐front positions are here used to construct ‘barcode patterns’ along former flowlines, allowing retreat patterns to be compared and frequency of moraine formation to be assessed. Since Younger Dryas glaciers in Scotland probably began to retreat around 12.1 ka and had disappeared by the early Holocene (11.5 ka), we assume time spans of 600–1200 years to calculate glacier retreat rates and to gain an understanding of marginal response to climate warming during the second half of the Younger Dryas. The calculations indicate that moraines formed every 3–23 years, depending, amongst other factors, on glacier size and basin topography. Retreat distances and the frequency of moraine formation have to be regarded as minimum values since sedimentological studies have shown that readvances were commonplace, i.e. two‐thirds of the ice‐marginal positions were occupied twice. Annual moraines might be present along short stretches, but are unlikely to occur throughout larger areas. This evidence indicates a palaeo‐environment dominated by very active glaciers with short margin response times similar to modern glaciers in maritime areas such as Norway or Iceland. Together, this evidence corresponds well with published data on the Younger Dryas palaeo‐environment in the far NW Scottish Highlands and in other areas such as the Isle of Skye and the central Grampian Highlands. The presented approach might help to fill gaps in the understanding of glacier dynamics in formerly glaciated areas elsewhere.

Key words:

• Moraines
• glacier dynamics
• deglaciation
• Younger Dryas
• Scottish Highlands