External Forces of the Earth Two Types Weathering

External Forces of the Earth

Two Types: Weathering and Erosion

Weathering Two Types – mechanical and chemical

Mechanical weathering • Rock is actually broken or weakened physically.

Mechanical weathering: Ex. -Frost Wedging • Water freezes to ice in a crack. • Ice widens the crack and splits the rock.

Mechanical weathering Ex. -Seeds • Seeds will take root and grow in the cracks of a rock. As the plant grows, the rock will split.

Chemical weathering • Alters the rock’s chemical make-up by changing the minerals that form the rock.

Chemical weathering: Example #1 • Water mixed with carbon dioxide from the air seeps into the cracks in certain rocks & dissolves the rocks away. • Examples: caves

Chemical weathering Example #2 • Acid Rain - Chemicals in the polluted water combine with water vapor and then fall back to the earth. • Destroys many things

Erosion 3 types

Wind

Wind Erosion • Moves dust, sand, and soil from one place to another. • Wears away the layer of soil that covers the earth’s crust • Plants help protect the land from wind erosion.

Wind Erosion • Wind grinds away rock and hills by blasting them with sand dirt

Glaciers

Glacial Erosion • As glaciers move they pick up rocks and soil • Change landscapes – destroy forests, carve out valleys, alter paths of rivers. • As glaciers melt, rocks and soil are deposited.

Water

Water Erosion • Rivers carve away at the surrounding land to create deep V-shaped valleys • Fast rivers can wash away soil and carry it down stream • River flooding can create floodplains – good farming!

Water Erosion • Ocean waves wear away shorelines As water flows, it cuts into the land.