Ch 10: Weathering and Soil Formation

What is weathering? Rocks on the Earth’s surface undergoing changes in appearance and composition

What are the 2 types of Weathering? Mechanical- physically changing rock into smaller pieces without changing its composition Chemically- breakdown of rock by changing its chemical composition

mechanical weathering? What are the types of mechanical weathering?

Types of Mechanical Weathering 1. Exfoliation (unloading)- process where sheets of rock peel or flake away

Example of exfoliation:

Types of Mechanical weathering 2. Ice wedge- occurs when water seeps into rocks and freezes

Ice wedging

Types of Mechanical weathering 3. Biological activity- the activity of organisms, including plants, burrowing animals, and humans that weather away rock

Weathering by plants

Weathering by sandmartins nesting in cliff

Types of Mechanical weathering 4. Abrasion- collision of rock with one another resulting in breaking and wearing away.

Abrasion takes place in many environments: fast-moving streams beaches subject to storm waves desert environments with high winds beneath glaciers that are loaded with fragments of rock.

Water-carried particles eating away at the rock

Storm waves have eaten away at the shoreline

The ocean waves have eroded this beach leaving behind a cliff as the soil was washed away

Observe the effects of mechanical weathering.

What are the Types of Chemical Weathering?

Types of Chemical Weathering 1. Hydrolysis: Change in composition of minerals when they react with water

Feldspar combines with H2O to form a common clay called kaolin

Types of Chemical Weathering 2. Carbonation – When some minerals come in contact with carbonic acid, they form a new product

Stalactites caused by carbonation Limestone is eaten away by acid and deposits as it drips from ceiling of cavern

Types of Chemical Weathering 3. Oxidation – When metallic elements combine with oxygen

Oxidation = rust!

Types of Chemical Weathering 4. Acid Precipitation “acid rain”

Types of Chemical Weathering 5. Plant acids – plants secrete acids that erode away the rock

Lichens and mosses grow on rocks and secrete weak acids that dissolve the surface

What 4 things affect the rate of weathering?

1. Rock composition Igneous and metamorphic rocks don’t weather easily Sedimentary rocks do

2. Amount of exposure More exposure it receives, faster it will weather Amount of time and amount of surface area exposed is also important

3. Climate Slow in very hot / very cold climates Fairly rapid in warm, humid climates

Cleopatra’s needle after only one century in New York City

4. Topography Elevation or slope of surface where rock is located affects rate of weathering