Chapter 1, Section 3

I. Changes on the Earth’s Surface Weathering Is the breakdown of rock at or near the earth’s surface into smaller and smaller pieces. Two types of weathering. Mechanical Chemical

a. Mechanical Weathering Occurs when rock is actually broken or weakened physically. Breaks large masses of rock into smaller pieces, producing boulders, stones, pebbles, sand, silt and dust. Most common type of Mechanical Weathering is known as Frost Wedging.

b. Chemical Weathering Alters a rock’s chemical makeup by changing the minerals that form the rock or combining them with new chemical elements. This means chemical weathering can change one type of rock into an entirely different type causing the loss of valuable minerals (leaching). Most important factors water and carbon dioxide. *** Acid Rain is another type of chemical weathering. Some known causes of acid rain are acid-producing agents from the ocean, volcanic activity and industrial pollution.

c. Observing Weathering Besides the effects on old stone structures such as tombstones, it also softens the sharp features on carved stone statues, and breaks down the mortar that holds together stone or brick walls. Weathering also changes natural landforms, jagged mountains can turn to rounded hills over millions of years.

B. Erosion The movement of weathered materials such as gravel, soil and sand. The three most common causes of erosion are a. water, b. wind and c. glaciers.

a. Water Moving water – rain, rivers, streams and oceans – (mixed with sediments AKA small particles of soil, sand and gravel) is the greatest cause of erosion.

b. Wind Caused the “Dust Bowl” during the 1930s. Drought caused soil to dry, wind blew and stripped the land of its minerals and nutrients. Sandstorms are major causes of erosion.

c. Glaciers Huge, slow-moving sheets of ice. While rivers cut sharp-sided, V-shaped valleys, glaciers carve out valleys that are rounded and U-shaped.