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Process of physical weathering:
Physical or mechanical weathering is the breaking down of rocks into smaller particles called regolith. Physical weathering does not change the chemical composition of the rocks. One process of physical weathering is freeze-thaw action . Freeze-thaw action is the most common type of physical weathering and occurs in mountainous areas where there are frequent temperature changes. It is also known as frost action. It is most likely to occur in areas where temperatures frequently rise above and fall below freezing and there is a plentiful supply of rainfall. During the day when it rains, water collects in the cracks or fissures in the rock. During the night when temperatures drop below 0� C the water freezes. When the water freezes its volume expands by about 10%. This puts pressure on the surrounding rock and the cracks are widened. When daytime comes the ice melts. Over time this repeated freezing and thawing of rainwater eventually causes the rock to shatter and crumble until it is completely broken down. This regolith moves down slope under the influence of gravity. This is known as mass movement. The weathered rock is known as scree or talus. Evidence of scree slopes can be seen on Croagh Patrick, Co. Mayo and on the Sugarloaf, Co. Wicklow.
Process of chemical weathering:One process of chemical weathering is carbonation . Sedimentary rocks such as limestone are chemically weathered by a process of carbonation. Rainwater picks up carbon dioxide as it passes through the atmosphere. The water and carbon dioxide combine to form a weak carbonic acid. The weak carbonic acid acts on the fissures in the limestone. Rocks such as limestone contain calcium carbonate. The calcium carbonate combines with the weak carbonic acid to form calcium bicarbonate. The soluble calcium bicarbonate is dissolved and removed in solution. The fissures in the limestone become enlarged and over time the limestone is dissolved. A limestone pavement is a large flat area of exposed limestone rock that had its soil cover removed, probably as a result of soil erosion or glacial erosion. Limestone is a well-jointed rock and rainwater settles in the joints in the rock. Rainfall or carbonic acid acts upon these joints through the process of carbonation. An example of a limestone pavement can be found in the Burren in Co. Clare.