Weathering

Two Types of Weathering Physical (also called Mechanical) Chemical

Physical Weathering A change in the size or shape of a rock without changing the chemical composition

How Does it Happen? Plant roots break rock Animals burrow into rock Water breaks down rock by friction

Freeze/thaw- water enters cracks in rocks, freezes and widens crack, melts- occurs again and again- eventually widening rock (also called Ice Wedging)

Exfoliation- wind blown particles hit rock, breaking off tiny pieces or sheets

Temperature Changes- expansion and contraction of rock can break it into smaller pieces

Chemical Weathering Breakdown of rock by agents that cause chemical changes in rock

Oxidation Produces rust Oxygen in atmosphere combines with metals in rocks

Carbonic Acid Carbon dioxide in atmosphere combines with water in atmosphere to form carbonic acid

Carbonic acid falls on ground and dissolves limestone, marble, or calcite Can produce caves

Hydrolysis occurs when water, usually in the form of precipitation, changes the chemical composition of a rock and creates less stable rocks that weather more readily.

Plant Acids Some plants produce an acid that reacts with rocks EX- lichen

A Brief Review Look at the following pictures and see if you can determine what type of weathering has occurred (physical or chemical) and then identify the specific process that caused the weathering.

Reading Guide Complete Reading Guide for 12.1

Pop Quiz 1. What is weathering? 2. What type of weathering causes breaks in rocks caused by the constant freezing & thawing of ice? 3. True or False. Rust caused by weathering. 4. Can carbon dioxide contribute to weathering?

Pop Quiz Mechanical or Chemical Weathering? 5. Limestone dissolved by carbonic acid. 6. Animal burrows dug in rock. 7. Formation of potholes in streets during severe winters. 8. The action of water, salt and air on car fenders.

The Rate of Weathering Chapter 8

What affects the rate of weathering? 1. Rock Composition Type of Rock Rate of weathering Sedimentary Metamorphic Igneous Quickly Slowly

What affects the rate of weathering? 2. Amount of Exposure - when higher % of rock is at surface of earth the faster it will weather Which landform will have greater surface area?

3. Climate Very Cold Climates Weathering takes place slowly

3. Climate Dry, Hot Climates Very slow weathering

3. Climate Warm, Humid Climates Chemical weathering fast

3. Climate Places where daily changes in temperature will accelerate weathering

4. Topography Altitude and slope of land will effect weathering.

What’s the Rate of weathering?

Pg 277 in book Numbers 23-27 and be ready for a quiz.

Quiz What type of rock weathers the fastest? What type of rock weathers the slowest? Would one rock or many rocks weather faster? Would rock weather fast or slow in a hot, dry area? In what region of the US (NE, NW, SE, or SE) would you find high rates of chemical weathering?

SOIL Weathered rock forms sediments Sediments and organic matter (humus) form SOIL

Soil Mixture of organic matter and weathered rock that forms over a long period of time

Factors affecting soil formation Climate Parent rock Organisms Relief (slope, topography) Time

Soil Profile Different layers of soil are called HORIZONS Horizons together make a PROFILE

Soil Horizons O horizon- uppermost layer, organic matter on top of soil A horizon- top soil layer, includes plant roots, dark in color, much organic matter (Also called the Zone of Accumulation)

Soil Horizons (cont’d.) B horizon- under A horizon, lighter in color, some organic matter (roots), some weathered rock (Also called the Zone of Leaching) C horizon- under B, mostly weathered rock

Parent rock- under C horizon, is the type of rock that weathers and produces the soil

Importance of Soil Location Residual soil- forms and stays in the same place Transported soil- forms in one place, is moved to another Transported is common

Soil Particles Classified by size 3 particle types sand = 2.0 mm - 0.02 mm silt = 0.02 mm - 0.002 mm clay = less than 0.002 mm

Soil Lab In groups of 3 or 4. 1. Carefully extract a soil sample using either a soil probe. Top of probe must touch the ground. 2. How many different soil layers do you see? 3. Describe each layer, color, composition (sandy, clay, etc.). 4. Label each layer horizons O-D and define each layer. 5. Which layer does vegetation grow in? 6. Which layer has a large abundance of nutrients? 7. Which layer is composed of leaf litter? All group members must turn questions and findings.