Drumlin formation by subglacial meltwater erosion
Some drumlins are shown to belong to a family of remnant erosional ridges associated with subglacial meltwater. The lengths of these ridges vary in scale from a few tens of millimetres to over 5 km. Similar form elements are illustrated for three scales of forms. It is concluded that some drumlins are composed of preexisting sediment or bedrock left upstanding in ridges as a result of the removal of surrounding materials. This erosional theory is related to an earlier theory in which drumlins are held to result from the infilling of subglacial cavities. The unifying factor for both theories is the role of sheets of subglacial meltwater.