It is usually expressed in terms of water gain or loss. They appear as dark streaks of rock along the glacier centerline. Rock debris deposited by a glacier. Neoglaciation refers to the advances made by mountain glaciers since the great Pleistocene ice age. In the Cascades the advances have occurred since 6,600 years before present.
Ogives are arc-shaped features occasionally found across the glacier surface below icefalls.
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.