| Term: | Till |
| Definition: |
Till is the unsorted rock debris deposited directly by the glacier without the extreme reworking by meltwater. As glaciers melt, their remaining load of rocks is distributed in several ways. Rocks may be dropped in place by the melting ice; they may be rolled to the ice margins, or they may be deposited by meltwater streams. Collectively, these deposits are called 'glacial drift'. 'Till' refers to the debris deposited directly by the glacier. Rock debris rolls off the glacier edges and builds piles of loose unconsolidated rocks called 'glacier moraine'. 'Lateral moraines' form along the side of a glacier and curl into a 'terminal moraine' at the glacier's downvalley end. Drift and moraines are valuable to geologists because they outline the boundaries of past glaciations.
An unsorted and unstratified accumulation of glacial sediment, deposited directly by glacier ice. Till is a heterogeneous mixture of different sized material deposited by moving ice (lodgement till) or by the melting in-place of stagnant ice (ablation till). After deposition, some tills are reworked by water. A poorly sorted mixture of mud, sand and gravel-sized material deposited directly from glacier ice. The principal types of till are basal, deposited beneath a glacier, and embracing lodgement till (plastered on the bed) and meltout till (released from slow-moving or stagnant ice); and supraglacial meltout till, let down onto the substrate from the glacier surface. Swisseduc Heterogeneous sediment deposited directly by a glacier. The particles within this deposit have not been size sorted by the action of wind or water. PhysicalGeography GCW |