They may be ridges and swales in the ice or bands of darker or lighter ice. Some glaciologists say that ice is a perfectly plastic substance. The period of earth's history, roughly two million years ago to about ten thousand years ago, characterized by the advance and recession of continental ice sheets. The upper sides are rounded and smoothed and the lower sides are rough and broken due to quarrying by the glacier. Seracs are the pinnacles of ice formed where the glacier surface is torn by sets of crevasses.
Striations are the scratches etched into the rock at the bed of a glacier.
Their presence indicates grinding of sand and rock particles into the bed under considerable pressure. In some places find-grained debris polishes the bedrock to a lustrous surface finish called glacial polish . A suncup is a small depression on a snow or firn surface formed by melting and evaporation resulting from direct exposure to the sun. A moraine formed at the downvalley end of a glacier. Piles of loose unconsolidated rock at the glacier's downvalley end.