How are Glacial Topography formed?

When glaciers in the form of continental glaciers (on lowlands or plateaus) or mountain or valley glaciers (in valleys or ice-caps on relatively isolated mountains or peaks cover land surface they produce distinct erosional and depositional features which characterise glacial topography. The erosional features occur in the areas occupied by ice. Depositional features occur in both the ice-covered areas as well as those beyond ice-margin through the agency of melt water.

Phenomenon of Ice Accumulation:

The phenomenon of ice accumulation starts with the lowering of temperature. When this happens the summer melt in higher altitudes and higher latitudes is not able to dissipate the snow that fell during the cold season. Bit by bit the balance of winter snow accumulation over dissipation in summer causes the formation of ice masses or snowfields of various dimensions.

Temperature during the Pleistocene:

The temperature in Britain during the Pleistocene in summer was about 11 Degree Celsius lower than now. That made all the difference between the present temperate climate of Britain and the Pleistocene glacial epoch when all Great Britain except a southern fraction about south of 52 degree north was ice-covered. The average temperature of the globe during the Pleistocene is believed to have been 10-20 degree Fahrenheit lower than now.

According to Fairbridge there is no reason to assume that the Pleistocene ice age is over. We may be only in an interglacial part of a longer ice age viz. the Quaternary ice age.

Pleistocene glaciation may be still continuing. The present ice sheets of Antarctica, Greenland, and the oscillating glaciation of the Pleistocene marked by glacial advances and interglacial retreats may support the continuity of the Quaternary ice age through the present times, into the future.

Earlier glaciations:

Prior to the Pleistocene, there were several glacial ages during the geological history of the earth. The oldest glaciation occurred during Middle Precambrian (about 1000 m years ago). The second glacial age belonged to the Late Precambrian and Cambrian periods. Next is believed to be an extensive glaciation during the Silurian and Devonian (confined to Africa and South America). The fourth major ice age occurred during the Permo-Carboniferous period. It was far more extensive than the Quaternary glaciation, covering about half4 the land area of the globe, whereas the maximum coverage was 30% during the Pleistocene, the present coverage being about 10%.

Ice coverage during various glaciations was, however, confined mainly to the southern hemisphere.

The belief that there have been more glaciations has not been supported by later investigations. The duration of the various glacial periods of the past is believed to have ranged from ten to fifty million years. The earlier glaciations are proved by lithified boulder clay, known as tillite.

Causes of Glaciation:

The causes of climatic, change, which are responsible for glaciation, are found discussed in books on climatology but are little understood. The causes, which are not our concern here, may be related to the variation in the insolation from the sun to the earth, changes in the composition of the atmosphere and changes within the globe. The changes in the globe include continental drift or rise of mountains to glacial heights.

Duration of Quaternary glaciation:

During the Quaternary glaciation the ice bodies of the globe expanded and contracted four or more times in 2-3 million years B.P. (before the present).

Glaciation and Glacierization:

Glaciation may be differentiated from the term glacierization. The latter means the coverage of an area by glaciers. During floods, water covers land. During glacierization ice inundates it. Glaciation refers to ice action on land. This may include erosion and deposition. Glacierization may be limited to the modern process of ice occupation. But ‘glaciation’ is so comprehensively and freely in use that it encompasses all the phenomena resulting from the occupation of land by ice masses and all the erosional and depositional consequences of ice action below, within the peripheral to the ice masses. As such the distinction between glaciation and glacierization may not be strictly adhered to.