Weathering is the process by which rocks are broken down into smaller pieces. There are two processes of weathering: mechanical and chemical. Mechanical weathering occurs when the rock is physically broken down into smaller pieces by environmental factors, whereas chemical weathering actually changes the chemical composition of the rock.
Definition
Mechanical weathering occurs when enough pressure is exerted upon a rock to force it to break into smaller pieces. In nature, this always occurs as the rock is exposed to different weather conditions, such as heat, ice, water and pressure. Unlike chemical weathering, the rock's chemical composition is still the same. The only change occurring during the process of mechanical weathering is the continual reduction of the size of the rock.
Heat-Induced Mechanical Weathering
Heat contributes to mechanical weathering by causing rocks to expand. This form of mechanical weathering is found most often in deserts, where the temperatures during the day and during the night are vastly different. The heat during the day causes the rocks to expand, while the coldness at night forces the rock to contract. This process of continual expansion and contraction causes stress on the outer layers of the rock. When enough stress is placed upon the outer layers, they start to peel off.
Ice-Induced Mechanical Weathering
Ice also causes rocks to expand. This form of mechanical weathering occurs in areas that have temperatures that regularly reach freezing. As water that seeps into the cracks of rock freezes, the expansion of the water as it turns to ice forces the cracks in the rock to expand further. The ice melts and reveals a larger crack, which is continually frozen and thawed in the same manner. The cracks then compromise the structural integrity of the rock and over time, force the rock to further split along those cracks.
Salt-Growth Weathering
Weathering through salt growths is similar to weathering through freezing and thawing. This form of mechanical weathering occurs in rocks found along the ocean coasts. When salt waters seep into rock cracks, it leaves behind salt crystals when the water evaporates. The salt crystals then expand when they are heated up, thus widening the cracks. Repeated encounters with saltwater also increase the amount of salt crystals found in the cracks. Given enough time, the enlarged cracks caused by the salt crystals result in the rock breakage.
Abrasion
Abrasion is another form of mechanical weathering, where the rock is literally rubbed down to smaller pieces. This form is also most commonly found in deserts where sandstorms cause sand particles to whip through the air at high speeds. The sand removes the upper layers of rock through friction, in the same way sandpaper smooths out objects. Unlike other methods, which require expansion and contraction of the rock or of its cracks, abrasion only require friction.
Tags: form mechanical, form mechanical weathering, salt crystals, smaller pieces, This form
