Warm – Up: What processes shape the surface of the earth?

•Notes: Weathering and Erosion

•WS: Weathering and Erosion

Agenda 2/4

Weathering and Erosion

Weathering: Process by which rocks on or near Earth’s surface break down and change

Types of Weathering:

1)Mechanical: process by which rocks and minerals break down into smaller pieces (does not change rocks composition, only size and shape.

2)Chemical: process by which rocks and minerals undergo changes in their composition as a result of chemical reactions

Weathering

1. Temperature: Drop in temperature causes water to begin to freeze, water then expands, taking up more space than in liquid form

- Frost Wedging: repeated thawing and freezing of water in the cracks of rocks causing them to break apart (example: Potholes)

Factors of Mechanical Weathering

2. Pressure: Layers of rocks put pressure on rocks below; when rock layers are removed (exfoliation), pressure is reduced, causing expansion of the rock and long, curved cracks to form

Exfoliation: outer rock layers are stripped away

Factors of Mechanical Weathering

1.Water: can dissolve many kinds of minerals and rocks; Can react with other substances (hydrolysis) which occurs during the decomposition of one mineral to another.

2. Oxygen: can chemically react with other substances (oxidation); ex: oxygen in the atmosphere can combine with iron in rocks and minerals

Factors of Chemical Weathering

3. Carbon Dioxide: atmospheric gas when combined with water in the atmosphere produces weak carbonic acid; can react with certain minerals to dissolve rocks

4. Acid Precipitation: caused by the oxidation of sulfur dioxide and nitrogen oxides in the atmosphere by human activity; has a pH below 5.6; creates problems for many organisms living in aquatic environments

Factors of Chemical Weathering

Climate: interaction between temperature and precipitation

-Chemical weathering: common in warm temps, abundant rainfall, lush vegetation

-Mechanical weathering: cool, dry climates where water undergoes repeated freezing and thawing

Rock Type and Composition: sedimentary rocks are more easily weathered than harder igneous and metamorphic

Surface area: more surface area=more weathering

Topography: slope of the landscape determines the weathering

What affects the rate of weathering?

Erosion and Deposition

Erosion: removal of weathered rock and soil from its original location

Deposition: After the material is transported they are dropped into another location

Erosion

Force of gravity tends to pull all materials downslope.

Without gravity, glaciers would not move downslope and streams would not flow

Also an agent in mass movements: landslides, mudflows, and avalanches.

Gravity’s Role in Erosion

**Swiftly flowing water has greater erosional power than wind and can also carry more material along with it and over a greater distance.

Rill Erosion: erosion by running water in small channels, on the side of a slope; form on a slope

Gully Erosion: when channel becomes deep and wide; can be more than 3 m deep and causes major problems in farming and grazing areas

**Weathering and Erosion occur also in oceans and islands: currents, waves, and tides carves out cliffs, arches, and more and a lot of the weathering and erosion occurs along the shorelines.

Erosion by Running Water

-Glaciers scrape and gouge out large sections of Earth’s landscape; they are so dense and have ability to carry huge rocks and other debris long distances

-Leave behind valleys with waterfalls, lakes, and variously shaped deposits of sediment

Glacial Erosion

Moving Masses of ice

Form near Earth’s poles and mountainous areas at high elevations

10% of Earth’s surface

Valley Glaciers: glaciers form in valleys in high, mountainous areas;

Continental Glacier: glaciers that cover broad, continent-sized areas; thickest at its center and much larger than valley glaciers

Glacial erosion

Most powerful erosional agent due to size, weight, and density.

Create U-shaped valleys (valley glaciers) and also scoop out deep depressions known as cirques

Switzerland’s Matterhorn: formed where there were glaciers on three or more sides of this moutaintop and this peak formed. (known as a horn)

- Major erosional agent in areas with limited precipitation and high temperatures

- Can easily pick up and move the fine, dry particles

- Effects can be dramatic and devastating

- Can damage natural features and human made structures

- Very common in Death Valley

- Shore areas also experience wind erosion

- Running water and glacial activity still more powerful

- Wind barriers can reduce the effects of wind erosion for farmers (trees and other plants)

Wind Erosion

Wind erosion and transport

Wind cant carry particles as large as those transported by water

Ability of wind to erode materials is less than that of other agents (i.e. water and ice)

Suspension: method of transport by which strong winds cause particles to stay airborne for long distances

Saltation: causes bouncing motion (sand transport)

Wind erosion and transport

Occur where there is little precipitation and vegetative cover (like deserts)

Can be major problem in the agricultural areas

abrasion (process of erosion): particles rub against the surface of rocks or other materials

Wind abrasion very effective agent of erosion

Ventifacts: rocks shaped by wind-blown sediments

Loess

Def: thick, wind blown silt deposits (another material wind also carries in great quantities and long distances)

Loess deposits located Illinois, Iowa, Missouri, South Dakota, Nebraska, Kansas, and Idaho.

With adequate precipitation, loess soils are some of the most fertile on Earth due to their abundance in minerals and nutrients

-Plants and animals move Earth’s surface materials from one place to another

-Animals burrow, humans excavate areas and move soil, planting a garden, developing new athletic fields, building a highway all result in the moving of earth’s materials from one place to another

-Effects of erosion by plants, animals, or humans is minimal compared to water, wind, or glaciers.

Erosion by Plants, Animals, and Humans