WEATHERING AND SOIL FORMATION, Study notes of Construction

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WEATHERING AND SOIL

FORMATION

8 th Grade- Mr. Stelma

WEATHERING EFFECTS

The surface processes that break down rock are called weathering. Weathering breaks rock into smaller and smaller pieces. Tiny moss plants, earthworms, wind, rain, and even oxygen weaken and break apart rocks at Earth’s surface.

http:// sizes.com/ natural/ particles_sedim entary.htm

There are two different types of weathering— mechanical weathering and chemical weathering. Both types work together to change Earth’s surface.

MECHANICAL PLANTS?

Water and nutrients collect in the cracks of rocks. Seeds that land in the cracks are able to grow. As a plant grows, its roots grow larger and move deeper into the crack in the rock. As the roots get bigger, they make the crack larger. (tree roots lifting and cracking a side walk)

MECHANICAL ANIMALS?

Small burrowing animals, such as moles, dig tunnels in the ground. Burrowing loosens small rocks and sediment in soil. The animal pushes these small pieces of rock to the surface. Once these small rocks and sediment are out of the ground, other weathering processes act on them.

MECHANICAL ICE

WEDGING

Ice wedging is the mechanical weathering process that occurs when water freezes in the cracks of rocks. Water may seep into a crack in a rock. As the water turns to ice, it expands and pushes against the sides of the crack. The crack gets wider and deeper. The pressure of the ice in the crack is so great it can break the rock apart.

MECHANICAL ICE

WEDGING CONT’

When temperatures rise, the ice melts. Because the crack is larger now, more water can enter the crack. When the water freezes again, the ice will again put pressure on the crack. After many years of this freezing and melting cycle, the rock will break up completely.

SURFACE AREA

vMeasure the surface area of the exposed area of the blocks stacked and the blocks separated.

SURFACE AREA

Breaking rocks into smaller pieces increases surface area compared to what the original rock had. As the surface area increases, more rock is exposed to water and oxygen. This speeds up a different kind of weathering, called chemical weathering.

CHEMICAL WEATHERING

Chemical weathering occurs when chemical reactions dissolve the minerals in rocks or change them into different minerals. Like mechanical weathering, chemical weathering changes the size and shape of rocks. But it also changes the chemical makeup of rock. These chemical changes weaken the rock.

CHEMICAL WEATHERING

CONT’

Naturally formed acids can weather rock. Carbonic acid is a natural acid formed when water reacts with carbon dioxide gas in the air or soil. Even though carbonic acid is a weak acid, it causes chemical weathering in rocks.

Other naturally occurring acids weather other types of rock. Granite, some types of sandstone, and other rocks all contain the mineral feldspar. Over many years, feldspar is broken down into a clay mineral called kaolinite. Kaolinite clay is found in some soils. Clay is an end product of weathering.

CHEMICAL PLANT

Some plant roots give off acids. Rotting or decaying plants also give off acids. These natural acids can dissolve minerals in rock. When the minerals dissolve, the rock is weakened. Over time, the rock cracks and breaks into smaller pieces. As the rock weathers, nutrients become available to plants.