Proglacial Lakes: During the de-glaciation period of a glacier, meltwater lakes form in front of glaciers. They are many hundreds of metres deep and are often surrounded with moraine.
Examples of these are Lake Lapworth in the Welsh borders, Lake Harrison in the Midlands and Lake Pickering in North Yorkshire.
Overflow Channels: Sometimes, proglacial lakes would overflow into other valleys and create another valley via fluvial erosion. These also drained the proglacial lakes when meltwater dried up.
The diversion of the River Severn
During pre-glacial times, the River Severn…