chapter 23: earth’s changing surface

Chapter 23: Earth’s Changing Surface

Objectives: •What is weathering & erosion?•Give examples of mechanical and chemical weathering.•How do weathering & erosion change Earth’s surface?•How do you “read” sedimentary rocks that are formed as a result of erosion and deposition?

WeatheringWeathering by wind and water causes rocks

to break apart into smaller pieces or SEDIMENTS (SEDIMENT = END PRODUCT).

Types of Weathering1. Mechanical – Rocks are broken apart

physically

•Water seeps into cracks of rocks and freezes when temps. drop.

•Ice expands and wedges apart rocks

Examples of Mechanical Weathering

1A. Frost Wedging

Hoodoos were created by frost wedging over a long period of time

Frost Wedging creates rock spires and pot holes.

Frost wedging happens in environment where temperatures alternate between hot and cold or where there are seasons

Examples Mechanical Weathering

1B. Abrasion =

Wind or water SCRAPES the surface of rock to break it up.

(sand blasting)

Examples of Mechanical Weathering

1 C. Plant roots – help break apart rocks

Chemical WeatheringRocks containing calcium (limestone,

marble, etc.) dissolve in acidic water.

Rain can be acidic because of dissolved carbon dioxide (carbonic acid)

Example:

Caves form in limestone rocks. Water seeps through ground and dissolves rock to form caverns.

ErosionErosion is when the sediments (made by

weathering) are carried away to a new location by wind or water.

AGENTS OF EROSION:

1.Water2.Wind3.Gravity

Mass Movements= Erosion w/ help of gravity. Once weathering has broken rock up, gravity can move rocks down slopes! (H2O usu. helps)

• Land slides – rapid, large amounts of rock & soil

• Mudflows – rapid, large amounts of soil, sediments & water

• Creep – gradual, soil moves down slope (alt. freezing & cold temps)

• Slump – rapid, small amount of hillside move down a “step” (Wet soil)

Types of Mass Movement (aka, mass wasting)

Sediments are deposited in layers and cement into new layers of sedimentary rock

Layer A was laid down first.

Then layer B.

Layer I is the most recent.

“Story of Rocks”

•Lower layers came first.

•Index fossils are used to guess the age of rocks.

•Magma intrusions come after the layers they cross through.

•Folding can change the direction of layers.