Glacial Till :: miscellaneous

frosty TillThe characteristics of glacial coin bank reflect the erosional, transportational and depositional history of the fragment sediment. flash-frozen manger is a heterogeneous mixture of rock fragments ranging in size from clay to boulders and is deposited directly from glacial ice without water transport. (Strahler A. H. & Strahler A. N. 1976). Ice sheets deposited in the Pleistocene period may be more than 30 m deep and inevitably the constituents of glacial till will reflect the retreats, advances and nonmoving phases of the ice which have taken place during the history of a glacier since its formation.I shall outline the various forms of glacial till, giving consideration to the type of overriding climatic conditions which give rise to their formation and deposition to illustrate how the constituent sediment does provide evidence for glacial activity over time.As glaciers are so effective at erosion and transport, large quantities of junk is also associated with t hem. According to its location with respect to the glacier, such dust transported as ice mass may be divided into trey main categories. There are three main positions that a glacier elicit transport debris, englacial debris which occurs within the glacier, supraglacial debris which occurs on the glacier move up and subglacial debris which occurs on the base of the glacier, (please look at figure 15.12 below). While debris is universe transported it may remain in any one of these positions until it is deposited by the ice directly or it may end up being reworked by conflate water. Deposition of the transported material is a complex process, that the fraction deposited directly from the ice is called till. It consists of a wide range of iota sizes, so it is often referred to as boulder clay. It also posses very littler stratification and frequently contains far travelled erratic material, which tends to have clast with edges and corners blunt by abrasion. (Briggs D. Et. Al . 1997)There are two main different types of till which have been recognised, lodgement till and ablation till. Lodgement till is rigid down subglacially when debris is released directly from the sole of the ice. Ablation till accumulates ab initio in a supraglacial position and is later lowered to the ground surface by undermelting. Ablation till can be further subdivided into meltout till and flow till. Meltout till is a direct product of ablation continue beneath a cover of detritus and flow till consists of debris that has built up on ice and after saturation with melt water becomes so unstable that it flows or slumps into near by hollows.