WEATHERING & EROSION

What is Weathering?

• Process by which rocks on or near Earth’s surface break down and change.

MECHANICAL WEATHERING

• Also called physical weathering.

• Changes rocks size and shape but NOT composition.

• EX:– Frost Wedging: freezing

water expands in rock causing cracks

– Pressure: • from tree roots • removal of rock layers

above. When rock layers are removed, rock can expand causing cracking.

CHEMICAL WEATHERING

• Changes rocks composition

• New minerals are formed

• Determined by– Composition of rock

• Calcite dissolves in acidic water

– Temperature• As temperature increases

so does rate of weathering

Water

• Hydrolysis- reaction of water with other substances.

Oxygen

• Oxidation- reaction of oxygen with water.

• Iron reacts with oxygen & creates rust

• Magnetite + oxgyen = hematite

Acids• Carbon dioxide,

nitrogen oxides, and sulfur dioxides from fossil fuels create acids in atmosphere.

• Cause acid rain.• These acids dissolve

minerals in rocks.• Can also tarnish

metals

WHAT AFFECTS THE RATE OF WEATHERING?

• Climate– Temperature &

precipitation in an area

– Chemical weathering more common where temperatures & precip are higher

– Physical weathering more common where dry, and cold (freezing & thawing occur more common)

• Rock type & composition– Hardness

– Sedimentary rocks more easily weathered than hard igneous or metamorphic

• Surface area– Mechanical weathering

breaks rock up into smaller pieces… creating more surface area for chemical weathering to occur

• Topography & other variables– Sloped areas expose

fresh rock after erosion. Fresh rock can then be weathered.

– Decaying organic matter releases CO2 which creates acid which weathers rock faster.

WHAT IS EROSION?

• Transporting weathered materials from one place to another.

WATER

• Steeper slopes, faster water flows

• Faster water flows, more erosion occurs

• Rill erosion- creates small channels

• Gully erosion- creates deep, wide channels

COASTAL EROSION

• Ocean waves & tides also cause erosion

• Constant erosion of beaches leads to creation of sand bars which eventually become barrier islands.

ICE

• Glaciers– Scrape out large

sections of earth’s landscape

– Carry large rocks & debris over many miles

WIND

• Occur in areas with limited rainfall and high temperatures

• Most of these areas have very little plant-life to hold soil in place

• Creates dunes

PLANTS, ANIMALS, HUMANS

• Minor impact compared to water, wind, glaciers

• When humans excavate land, cause erosion, leads to water pollution

• When animals burrow, shovel dirt somewhere else.

DAILY QUIZ #11. The breakdown of rocks is

a. Erosion b. Weathering c. Mass wasting

2. Oxidation is a form of a. Mechanical weathering b. Chemical weathering

3. When a rock changes in size & shape but not composition, it went through

a. Mechanical weathering b. Chemical weathering

4. Wind erosion can createa. Glaciers b. Mass wasting c. dunes

5. Coastal erosion results froma. Ocean Wavesb. Glacier formationc. Chemical weathering