Consider the 4 marked locations (A – C) in the figure. You should rank these loc

Question

Consider the 4 marked locations (A – C) in the figure. You should rank these locations (from fastest weathering to slowest weathering).

6 Homework utor: Weathering and Rates of Weathering The map below shows three different soils in terms of their dryness: desert, forest and wetlands. Deserts are too dry to support much vegetation-here, water is present but limited: forests receive enough rainfall to support large tree 3 of8 populations, and wetlands are inundated with water either seasonally or permanently. Consider the marked locations in the figure below. Rank these locations based on rates of weathering as a function of climate. NOTE: Moisture is more important than temperature. Canada Desert soil Grassland soi Forest sol Wetland soil Weakly developed soll Bare rock United States Ice or water Mexico Puerto Rico

Explanation / Answer

Weathering causes breakdown of the parent material into finer particles called sediments.  Erosion is when these sediments are transported by wind or water and deposited at another location. From the figure given above, it is evident that the point A, B and C denotes Forest soil, Desert soil and wetland soil respectively. So, the weathering rate is likely to be Desert > Wetlands > Forests. This means the rate of weathering will be the most in desert soils then in the wetlands and the least in forest soil. This is because:

Desert: The two main types of weathering occuring in deserts are Mechanical weathering, which is the disintegration of a rock by mechanical forces without changing the rock’s chemical composition and Chemical weathering, which is the decomposition of a rock by the alteration of its chemical composition. Together with these, there are four main types of Physical weathering, which occurs in deserts namely Exfoliation, granular disintegration, frost shattering and block separation.  Frost shattering occurs in areas where there is moisture and where the temperatures fluctuate above and below freezing. Physical weathering processes are considered to be more important in arid environments as they weather the rock at a very faster rate. It is said that chemical weathering is of less significance than Mechanical weathering in the desert areas because most forms of chemical weathering requires moisture and water and as deserts have very small amounts of precipitation, there is no water to create chemical reactions required for the chemical weathering processes. However, recently we geologists have come to know that chemical weathering is becoming increasingly recognized in deserts as hydrolysis occurs at a larger rates in deserts which is caused by the high levels of moisture at night. Without abundant water in the arid environment, the chemical breakdown of rocks proceeds extremely slowly relative to their equivalent rocks in humid climates.

Wetlands: An area that is more or less often saturated with surface water or groundwater for a long enough duration, to support vegetation that is adapted to grow in saturated soil conditions is referred to as wetland. Soils that develop in wetlands are called hydric soils. These areas are permanently or seasonally saturated with water and at places the rate of erosion equals the rate of sediment deposition, so the cycle is in a state of equilibrium which means the wetlands are neither being eroded nor growing. Here, the ground remains partially or fully saturated. .

Forest: The rate of weathering is the least in the forest owing to the huge number of trees present there. Plants typically cover the entire landscape in a forest and binds the soil, and hence prevent weathering. The roots of the trees act as anchors and holds the soil together.

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