Glaciation refers to covering of land by glaciers. Indirect impacts of glaciations include subsidence of crustal and rebound, changes in sea levels, rivers and valleys, and creation of proglacial lakes through ice dams. Subsidence of crustal and rebound happens in the main areas of ice accumulation leading to rising of land in these areas(Benn " Evans, 2014).The rise in the ground is because of excessive added weight by the ice leading to down warping of the crust of the Earth. If the ice melts or removed, the crust of the earth gradually rebounds to compensate for the lost weight.
Another indirect effect changes in the sea level. During formation of glaciers, sea water is taken and in the process reducing the sea level, and when it melts, it increases the sea level. Changes in valleys and reverse is another indirect effect as glaciers forms sources of many rivers and may modify the shape and size of valleys. (Benn " Evans, 2014). The final indirect effect is the creation of Proglacial lakes which are forced through glaciation ice dam by trapping melted ice and blocking river flow.
Dunes assume a consistent shape and their formation is by the direction of the wind, availability of sand and vegetation, and the velocity of the wind(Leuschner " Ellenberg,2017 ). Cross-bedding can be used to identify ancient dunes. Layers of sand usually depict the direction of wind flow (cross beds). The cross bed can be found in sediments when dunes are buried under another layer of sediment.
Barchans dunes are crescent shaped with the tip pointing downwind. The formation is due to limited sand supply on a hard, flat surface without vegetation. They are modest forming at a rate of 15 meters per year reaching a maximum height of 30 meters. The tip can be symmetrical if the wind is constant or one side can be lager if the wind is not consistent. Transverse dunes or sand sea, on the other hand, are found where there is plenty of sand, constant wind without vegetation on the surface. Troughs separate long ridges formed at right angles to the prevailing wind. The third type of dune is longitudinal dunes, formed in places with moderate sand (Leuschner " Ellenberg,2017 ). They form long ridges that are parallel to the prevailing wind. The fourth type of dune is parabolic dunes. The formation is along the coastline because of extreme supply of sand and strong onshore winds. Vegetation is present on the surface, deflation blowout the sand. The sand is then transported out of the depression. This sand is deposited in and grows larger with increased deflation.
References
Benn, D., " Evans, D. J. (2014). Glaciers and Glaciation. Abingdon: Routledge.
Leuschner, C., " Ellenberg, H. (2017). Sand Dunes and Their Vegetation Series. In Ecology of Central European Non-Forest Vegetation: Coastal to Alpine, Natural to Man-Made Habitats (pp. 63-115). Springer, Cham.
