1.1 Subglacial LodgementDalam buku karangan Nichols, dituliskan bahwa glasier bergerak akibat adanya deformasi internal dalam tubuh glasier hal ini karena sifat massa es yang padat yang cenderung mempertahankan posisinya ketika deformasi akan terjadi. Defomasi ini dipicu oleh gaya berat (gravitasi) ketika massa es bertambah dan tidak stabil lalu adanya shearing (gaya gesek) yang terjadi dapat menyebabkan panas dan ada bagian dalam es yang mencair yang menyebabkan diskontinuitas dalam tubuh glasier dan mengakibatkan akibatnya glasier dapat bergerak secara perlahan. Pressure-melting allows material to be released from the dirty basalt ice, particularly on the eupstream side of bumps. Together with basal shear within the ice/debris mixture, which facilitates renewal of the debris supply, this process leads to debris being plastered on to the bedm and progressively built up. This process known a lodgement, occurs both on bedrock and older till surfaces and leads to the filling of bedrock irregularities, so smoothing out the glacier bed. Some till may be squeezed into cavities down stream of a bump. Lodgement occurs beneath both advancing and receding glaciers, and the details are now well established from studies by Boulton on glaciers in Soutsbergen. A overrides the unconsolidated deposit. Where preserbed in older deposits, the pattern of such structures is potentially useful as a palaeo-ice flow indicator. Shear stress also results in the orientation of stone in the till developing at an angle of 45 to the bed (parallel to the olane of maximum sher stress), but as the material continues to deform, stones rotate so that they tend to approach parallelism with the bed thus providing an additional means of establishing the direction of flow in old lodgement tills. Deposition of lodgement till may be strongly affected by the transfer of debris-rich basal ice into an englacial or even supraglacial position by movement along shear or thrust zones within glacier undergoing compressive flow. Strictly speaking, the subsequent release of such deposits is by the melt-out process. The rate of subglacial till deposition can be considerable and 6m per century is regarded as reasonable. Contrary to the belief of glaciologists up to about 20 years ago, it is now known that much of the Antartic and Greenland ice sheets are at the pressure melting point at their base. Thus, the deposition of thick tills an dtillites on a continental scale as recorded in Pleistocene and earlier successions is not difficult to explain.

1.2 Melt-Out & FlowageMelting out of debris can occur either subglacially or supragacially, a process that is particularly active at the margins of glaciers and ice sheets, where the ice is practically stagnant. Geothermal heat is largerly responsible for the deposition of subglacial melt-out tills. If the water is able to escape without disturbing the sediment, the resulting till may preserve traces of the original relationsip of debris to the ice structures, Melt-out till is commonly deposited is unstable situations and is thus prone to flowage. During the past 50 years, frequent reference has been made to the possibility of flowage of saturated of saturated till at the base of a glacier. For example, Gripp suggested that some englacial bands were the result of till being squezzed up into basal crevasses, a process has observed in action. Hoppe (1957) has identified certain types of hummocky moraines resulting from same process. More recently, Boulton has noted that flowage can occur where thick unfrozen subglacial till exist beneath temperature ice. Basal crevasses are not particularly common beneath glaciers, as it happens unless the ice is at an advanced stage of decay, but there are other spaces into which till can be squeezed, in particular hollws down stream of obstacles abandones subglacial stream channels and moulins. Stones in wet lodgement till may undergo re-orientation if subsequently affected by flowage and the final fabric may be very different from till that has not been affected. Features of plastic deformation, particularly folds, may aid the recognition of such till. Debris at the surface of a glacier may have a basal derivation, especially near the margins of cold glaciers and ice sheets or in the case of valley glaciers it may have accumulated as a result of subaerial weathering of rock faces. This debris melts out in summer as a result of ablation.A layer of debris generally retards melting of dirty ice in comparison with clean ice, so the resulting ice surface tends to acquire debris ridges. As the debris is lowered it tends to undergo sliding and re-orientation, and rarely reflects the original fabric in the ice after depositions as till. A thick layer of supraglacial debris tends to be unstable and as with basal melt-out till is often capable of flowage. Regardless of whether the sediment is deposited supraglacially or subglacially, the process is particularly common near the snouts of receding or stagnating glaciers. The process has been particularly common near the snouts of receding or stagnating glaciers. The process has been particularly well studied by Bolton at the margins of various Spitsbergen glaciers and by Lawson at the snout of Matanuska Glacier in Alaska. The principal factors affecting debris flowage are the gradient of the bed on which it rests, whether it be ice or the glacier bed itself, the bed roughness, the amount of meltwater available for enabling the debris to become more fluid and the fabric of the debris itself. Saturated till may flow on the gentlest of slopes. According to Boulton, three types of flow can be distinguished which in decreasing order of rate of movement area. Mobile flow : in which stones may tend to settle towards the bottom producing a crude sorting patternb. Semi-plastic flow : which often begins by slope failure along an arcuate slipface and is perceptible as a slow-moving lobate tongue-boulders may sink, fold structures may form and washing by meltwater may produce laminations. c. Downslope creep : which involves less water and is not perceptible to the eye-although the till has a fabric that is subject to alteration and may acquire a weak foliation, it is unlikely to develop fold structure. Such till, in contrast to other types of flow till is compact and massive. 1.3 Sublimation of debris-rich ice

Sublimation is the process of ablation whereby ice is vaporized directly without passing through the intervening liquid phase. Some authors have claimed it to be of negligible importance, but in the cold, arid parts of Antartica, such as the Dry Valleys of Victoria Land where temperatures rarely exceed 0C, it is a common process. Here debris-rich ice ablates from te surface downwards, producing a loose sublimation till which inherits the foliated structure from the ice. Outside Antartica the process is rare, however.