The last glaciers (Loch Lomond Advance) in Snowdonia,N. Wales

Evidence for 35 former cwm glaciers has been mapped in Snowdonia, N. Wales. Glacial limits are based on end moraines, boulder and drift limits, and the down-valley extent of hummocky moraine. Protalus ramparts indicate that at least 16 semi-permanent snow beds down to altitudes of 150 m also existed. Radiocarbon dates and pollen stratigraphy indicate that the glaciers and snow beds belong to the Loch Lomond (Younger Dryas) Stadial. The existence of a large number of ‘Older Series Moraines’ is questionned. Glacier reconstruction and contouring allows calculation of fan line altitudes, and trend surface analysis indicates that they rise from 450 m in the southwest to 700 m in the northeast. It is inferred that mean July temperature at sea-level was around 8·5°C. Two differences between north and south Britain are recognized. Firstly in Snowdonia, as in the Lake District and Southern Uplands, the dominance of southerly air streams appears less than in the Scottish Highlands. Secondly, whereas in the Scottish Highlands, the glaciers appear to have stagnated in situ following initial active retreat, some of those farther south were active during much of the time their margins retreated.