New Geography in Action Junior Cycle Geography Weathering
Weathering is the breaking down of rocks and soil that are exposed to the weather. The broken-down material does not move from the place where the weathering occurred. There are two types of weathering:
• Mechanical weathering • Chemical weathering
Erosion Erosion is the breaking down of rocks and soil and the transportation of the eroded material. Erosion is caused by:
• Moving water (rivers/seas): see Chapters 9 and 10 • Moving ice (glaciers): see Chapter 11 • Moving air (wind): see Chapter 13
Mechanical weathering
Mechanical weathering breaks up rocks into smaller pieces by putting pressure on the rock. Freeze-thaw action is an example of mechanical weathering.
Freeze-thaw action Freeze-thaw action occurs high up in mountainous areas where there is a lot of precipitation (rain, sleet or snow) and the temperatures regularly rise above and fall below freezing point (0 ºC). Temperatures that repeatedly rise and fall are called fluctuating temperatures.
1 2 3 Scree
( Figure 6.2 Freeze- thaw action
1 During the day, water seeps into cracks in the rock.
2 At night, temperatures fall below freezing point. The water in the cracks freezes and expands by 9 per cent, putting pressure on the rock.
3 This process continues over time, widening the cracks and joints in the rock, causing it to weaken, and eventually pieces break off. The broken-down rock is known as scree. Scree often builds up at the base of a slope.
Example: Freeze-thaw action occurs in upland areas like Croagh Patrick in Co. Mayo. Temperatures here frequently rise above and fall below freezing point.
