Unit 8 : Weathering, Erosion, and SoilsA. Soil

1. Soil is the result of weathering of rocks and includes weathered particles : sand, silt, and clay2. A soil texture triangle is used to classify soil texture using the different proportions of sand, silt,

and clay in a sample

B. Physical Weathering1. Physical (or mechanical) weathering – occurs when physical forces break rocks into smaller and

smaller pieces without changing the rock’s mineral compositiona. Ex. tearing a sheet of paper

2. Frost wedging – rock breaks into pieces after many freeze-thaw cyclesa. most common in mountainous regions in middle latitudes

3. Unloading – large masses of igneous rock may be exposed through uplift and erosion of overlaying rocks

a. the outer rock masses separate and break into smaller pieces

4. Biological activity – activities of organisms such as plant growth, burrowing animals, and humans can cause physical weathering

C. Chemical Weathering1. Chemical weathering – transformation of rock into

one or more new compoundsa. Ex. Burning a sheet of paper

2. Water promotes chemical wreathing by absorbing gases from the atmosphere and the ground

a. these dissolved substances then chemically react with various minerals

b. ex : iron oxide is rust that forms when iron containing objects are exposed to water

D. Rates of Weathering1. Physical weathering speeds up the process of chemical weathering by increasing the surface area

of the exposed rock 2. High temperatures and abundant

moisture creates the most favorable climate for chemical weathering

3. Different parts of a rock mass weather at different rates depending on mineral composition and the number of cracks

E. Erosion1. Erosion – process by which Earth materials are carried away and redeposited by wind, water,

gravity, or icea. plucking –lifting up and moving fragments of rocksb. abrasion – scouring actions of particles carried by the windc. Humans move things from place to place due to construction, deforestation, and

agricultural practices

2. Water a. The higher the speed of the water, the greater the mass of material will be movedb. Coastlines are constantly eroded by waves causing loss of

coastlinec. Water forms river systems by eroding rock and moving

sediment downstreamd. Water will create canyons like the Grand Canyone. Erosion by water is the most common form of erosion

3. Winda. Causes erosion by plucking and abrasionb. Erosion through wind will cause landforms such as sand

dunes

4. Icea. Glaciers move sediments by abrasion or pluckingb. Landforms left by glaciers include deep rounded valleys, bowl valleys, and sharp pointed

mountain ridges5. Gravity

a. Creates landslides, mudslides, and avalanchesb. Gravity is constantly pushing materials down which causes loose sediments to erode

F. Precautions1. Landslide

a. Be aware of landslide susceptible areas in your neighborhood and recognize landslide warning signs

b. If you see signs of a landslide contact your local authorities, your neighbors, and evacuatec. If you are caught in a landslide, curl up into a ball and protect your head

2. Earthquakesa. If your areas is prone to earthquakes : secure tall or heavy furniture to the wall, and latch

cupboards so that plates and glass do not fall outb. During an earthquake, stay indoors, move away from windows and anything that can fall

on you and duckc. If you are outdoors, move quickly and safely into an open space away from electrical

lines, trees, and buildings3. Tsunami

a. Plan an evacuation route, follow local authorities directions, and seek higher ground4. Sinkholes

a. Sinkholes are caused by rock that is dissolved by weak natural acids found in rain and pore spaces in soil

b. Check for limestone deposits and be aware of past sinkholes in the area

5. Groundwater pollutiona. Test groundwater before consumption or use

6. Flooding a. Be aware if you live in a flood plain areab. Move to higher groundc. Do not walk, swim, or drive through swift moving water