What is lodgement till




















There are muddy rivers issuing from the glacier in several locations, depositing sediment on land, into Vitus Lake, and directly into the ocean. There are dirty icebergs shedding their sediment into the lake.

And, not visible in this view, there are sediments being moved along beneath the ice. The formation and movement of sediments in glacial environments is shown diagrammatically in Figure There are many types of glacial sediment generally classified by whether they are transported on, within, or beneath the glacial ice. The main types of sediment in a glacial environment are described below.

Supraglacial on top of the ice and englacial within the ice sediments that slide off the melting front of a stationary glacier can form a ridge of unsorted sediments called an end moraine.

The end moraine that represents the farthest advance of the glacier is a terminal moraine. Sediments transported and deposited by glacial ice are known as till. Subglacial sediment e. It has a wide range of grain sizes, including a relatively high proportion of silt and clay. The larger clasts pebbles to boulders in size tend to become partly rounded by abrasion.

When a glacier eventually melts, the lodgement till is exposed as a sheet of well-compacted sediment ranging from several centimetres to many metres in thickness.

Lodgement till is normally unbedded. An example is shown in Figure Supraglacial sediments are primarily derived from freeze-thaw eroded material that has fallen onto the ice from rocky slopes above. These sediments form lateral moraines Figure Medial moraines are visible on the Aletsch Glacier in Figure Most of this material is deposited on the ground when the ice melts, and is therefore called ablation till , a mixture of fine and coarse angular rock fragments, with much less sand, silt, and clay than lodgement till.

When supraglacial sediments become incorporated into the body of the glacier, they are known as englacial sediments Figure Massive amounts of water flow on the surface, within, and at the base of a glacier, even in cold areas and even when the glacier is advancing.

Depending on its velocity, this water is able to move sediments of various sizes and most of that material is washed out of the lower end of the glacier and deposited as outwash sediments. These sediments accumulate in a wide range of environments in the proglacial region the area in front of a glacier , most in fluvial environments, but some in lakes and the ocean. Glaciofluvial sediments are similar to sediments deposited in normal fluvial environments, and are dominated by silt, sand, and gravel.

The grains tend to be moderately well rounded, and the sediments have similar sedimentary structures e. A large proglacial plain of sediment is called a sandur a. Year: KarstBase a bibliography database in karst and cave science. Chemistry and Karst , White, William B. The karst paradigm: changes, trends and perspectives , Klimchouk, Alexander.

The use of damaged speleothems and in situ fault displacement monitoring to characterise active tectonic structures: an example from Zapadni Cave, Czech Republic , Briestensky, Milos; Stemberk, Josef; Rowberry, Matt D.

See all featured articles. Featured articles from other Geoscience Journals. Karst environment , Culver D. Microbial mediation of complex subterranean mineral structures , Tirato, Nicola; Torriano, Stefano F. See all featured articles from other geoscience journals.



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