MWC recognition

MWC systems

MWC types

Rammer Cleugh - a classic MWC

Cairngorm MWCs

 

A dry channel cut by meltwater near Halls, East Lothian

 

 

Meltwater channel erosion

The dimensions of large rock-cut meltwater channels point to efficient and probably rapid erosion. Clues as to the processes of erosion come from observations of relict meltwater channels and from modern glaciers.

The up-down profile of some large meltwater channels requires that meltwater has been moved locally up-gradient in tunnels beneath the ice. Uphill flow requires water moving rapidly under hydrostatic pressure. Under these circumstances cavitation can occur. Turbulent flow creates short-lived gas bubbles which collapse, producing a shock wave. Cavitation removes blocks and flakes from the bed and walls of the meltwater channels and may leave pot holes and sichelwannen.

In modern glaciers, the meltwater emerging from tunnels at the ice front is often highly charged with debris. The high flow velocities allow the movement of large boulders as bed load but a large amount of finer material may also be carried in suspension. Erosion is concentrated at the channel floor because of the huge throughput of debris and the resulting abrasion and block entrainment. The channels walls may also be smoothed and polished by the abrasion of rock flour, sand and fine gravel.