knob-and-tail
Quick Summary
A "knob-and-tail" is a geological feature formed during glacial abrasion. It occurs when a rock contains harder spots within softer surrounding material. As the ice moves, the softer rock erodes away, leaving the harder parts as protruding knobs. These knobs then protect the softer rock on their down-ice side, forming a tail that points away from the knob towards the glacier's margin. The size of a knob-and-tail feature depends on the size of these rock inhomogeneities, ranging from millimeters to meters. This feature helps determine the direction of ice movement.1
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