Glaciers have formed many geographical features.
Geologists know the Earth underwent several long ice ages due to evidence collected from preserved rocks and glaciers. The sedimentary deposits include glacial diamicton and dropstone deposits. The glacier-deposit sediment characteristics are influenced by the type of glacier, the thickness of the glacier, the amount of bedrock and the climate. Deposits are often trapped under the glacier and then are left behind when the glacier melts.
Time Frame
The Earth has experienced at least five major ice ages. According to professor of geology James S. Aber, some of the ice ages lasted as long as 100 million years and usually lasted at least tens of thousands of years. Through these ice ages, several glaciers formed that expanded and contracted over the course of millions of years.
Lodgment
Glacial deposits falls into one of two categories: lodgment and melt out. Lodgment deposits are formed based on glacial pressure and the flow conditions of the glacier. The glacier can apply constant pressure to the deposit and move at increasing velocity, causing bedrock erosion. The thickness of the lodgment deposit can be great enough to create a bed of sediment, upon which the glacier rides. This bed of sediment is called basal till.
Melt Out
The sub-glacial melt-out deposits get trapped under the ice. According to the University of Montana, the deposits left over from the glacial melt show the amount of sediment that the glacier was transporting during the melting, since the melting releases the carried sediment. The glacier sediment load influences how fine or coarse the leftover sediment is.
Marginal Deposits
Supra-glacial melt-out deposits can be found at the margins of the glacier. The sediment is left wherever the melting glacier edges happen to be. At the edges, there are fewer fine pieces of sediment because the melted water carries the fine pieces away, leaving behind more coarse sediment. This melt out can sometimes create large boulders of sediment as more and more sediment gets trapped in one central location during the melt out.
Geography
The Gowgonda Formation in Ontario has preserved a deposit of glaciogenic strata that is 2,300 million years old. This formation came from the Huronia Ice Age. There are other glacial deposits in Wyoming, Michigan, Quebec and throughout the Northwest Territories. The rocks demonstrate the continental glaciation that occurred for 400 million years, with at least three glacial expansions.
The Stuartian-Varangian Ice Age was the greatest of all and lasted between 600 million and 950 million years, leaving behind glacial deposits in Africa, Europe, Arabia, Australia and North America. Most of the deposits left behind by the Andean-Saharan Ice age eroded away in the Sahara. However, there are good sedimentary deposits in Arabia.
Tags: million years, deposits left, fine pieces, glacier sediment, leaving behind
