Glacial Transport

冰川运输大量的岩屑, including large boulders, gravel, sand, and fine silt. The glacier may carry this at its base, on its surface, or internally. Glacial deposits are characteristically poorly sorted or nonsorted, with large boulders next to fine silt. Most of a glacier's load is concentrated along its base and sides, because in these places plucking and abrasion are most effective.

Active ice deposits till as a variety of moraines, which are ridgelike accumulations of drift deposited on the margin of a glacier. Aterminal moraineis the farthest point of travel of the glacier's terminus.Glacial debrisleft on the glaciers' sides formslateral moraines, whereas where two glaciers meet, their moraines merge into amedial moraine.

Rock flour is a general name for the deposits at the base of glaciers, where they are produced by crushing and grinding by the glacier to make fine silt and sand. Glacial drift is a general term for all sediment deposited directly by glaciers, or byglacial meltwaterin streams, lakes, and the sea. Till is a type of glacial drift deposited directly by the ice and characterized by a nonsorted random mixture of rock fragments. Glacial marine drift is sediment deposited on the seafloor from floating ice shelves or bergs and may include many isolated pebbles or boulders that were initially trapped in glaciers on land, then floated in icebergs that calved off fromtidewater glaciers. These rocks melted out while over open water and fell into the sediment on the sea bottom. These isolated dropstones are often one of the hallmark signs of ancient glaciations in rock layers that geologists find in therock record. stratified drift is deposited by meltwater and may include a range of sizes, deposited in different fluvial orlacustrine environments.

Glacial erratics are glacially deposited rock fragments with compositions different from underlying rocks. In many cases the erratics are composed of rock types that do not occur in the area where they are located but are normally found only hundreds or thousands of miles away. Many glacial erratics in the northern united states can be shown to have come from parts of Canada. some clever geologists have used glacial erratics to help them find mines or rare minerals that they have located in an isolated erratic—they used their knowledge ofglacial geologyto trace the boulders back to their sources following the orientation ofglacial striationsin underlying rocks. Recently diamond mines were discovered in northern Canada (Nunavut) by tracing diamonds found inglacial tillback to their source.

sediment deposited by streams washing out ofglacial moraines, known as outwash is typically deposited bybraided streams. Many of these form on broadoutwash plains.When glaciers retreat,负载减少,系列of outwash terraces may form.

Continue reading here:Ice Caps

Was this article helpful?

+1 0