Weathering and Erosion

Mrs. Degl4 Weathering, Erosion, Deposition, and Landscapes Weathering – the mechanical and chemical processes that change objects on Earth’s surface over time. Weathering breaks down the rocks, erosion moves the particles, and deposition drops the sediments in another location. Erosion – the removal of weathered material from one location to another; the sediments are transported by wind, gravity, glaciers, man, and running water. Deposition – the process whereby these sediments are released by their transporting agents (dropped).

Weathering – responsible for limited changes in Earth’s surface – dissolving, crumbling or weakening a rock. Can take thousands of years. Two forms – physical and chemical

Erosion – responsible for large scale changes in the form of the Earth. Rivers, valleys, and canyons are created by the erosion of weakened or disintegrated rock. Can take thousands of years or minutes.

Water is a major factor in weathering. Rain splashes mud Puddles form

Water flows along surface, moving downhill. Little water paths become rills. Rills deepen into creeks, then streams, and finally, rivers. Water digs deeper channels and carries more earth and rock from shores and bottom.

Stream

Large river

13 There are two primary types of weathering: Chemical and Physical 1. Physical Weathering – the breakdown of rocks and minerals into smaller pieces without a change in chemical composition. Causes of physical weathering: 1. Freeze/thaw 2. Wedging by plant roots 3. Day/Night temperature fluctuations 4. Loss of thin surface of rocks by exfoliation or abrasion 5. Gravity causing rocks to fall from heights and then breaking into pieces 6. Animals, including people, digging into rocks

Freezing & Thawing When water in the cracks of rocks freezes it expands causing the crack to enlarge or get bigger. The ice melts & refreezes over & over, breaking the rock apart.

Result of Freezing & Thawing

Mrs. Degl16 Wedging by plant roots

Day/Night Temperature fluctuations

Exfoliation

Abrasion, wind erosion

Gravity Old Man in the Mountain, NH before May 5, 2003 After May 5, 2003

Animal actions

Physical weathering exposes new surfaces and pieces. New surfaces can be physically or chemically weathered 22

23 2.Chemical Weathering – Decomposition of rock material due to the chemical reaction of compounds in the rock with chemicals in the environment. Not all rocks are composed of the same chemicals or minerals, so chemical weathering affects different rocks differently.

24 Chemical weathering occurs at the surfaces of rocks. When physical weathering results in freshly exposed rock surfaces, agents of chemical weathering have new material to decompose.

Mrs. Degl25 Chemical Weathering occurs when elements and minerals in rocks react with chemicals from the environment. The rock breaks down at the same time as it changes chemical composition. The end result is different from the original rock. There are 3 main types of chemical weathering: 1. Oxidation – oxygen combines with the elements in the rock and it reacts. This the scientific name for rust. 2. Hydration – water reacts with the minerals in rocks and can dissolve certain minerals. 3. Carbonation – carbon dioxide dissolves in water to form carbonic acid. This makes acid rain which chemically weathers (dissolves) rocks. Other acids, like sulfuric acid, also combine with water to make acid rain.

26 Chemical Weathering: H 2 O + CO 2  H 2 CO 3 water + carbon dioxide  carbonic acid Statue created in 1702, Germany Picture on left, taken 1908 (after 206 years) Picture on right, taken 1969 (61 years later)

Mrs. Degl27 2. Particle Size – Larger particles weather slower and smaller particles weather at a faster rate. There are 4 factors that effect the rate of weathering: 1. Surface Area (exposure) - Exposing more surface area will increase the rate of weathering. 3. Chemical Composition (what a rock is made of) – Certain rocks and minerals are naturally weaker than others, while others are more resistant (stronger). 4. Climate – Warmer, moister climates have the most weathering. Heat & water speed up all chemical reactions. This is the most important factor in weathering.

Mrs. Degl28 Erosion (transport) There are 5 main agents of erosion: 1.*Running Water* 2.Glaciers 3.Wind 4.Gravity 5.Man Weathering has to happen before erosion. The rocks have to be broken into smaller sediments before they can be eroded away. Wind Erosion Glacier

Mrs. Degl29 Mount Rushmore There is a pile of weathered material at the bottom. It is slowly being eroded down hill by gravity. It will not be there forever!!

Water, wind, or gravity exert a force on the soil material, causing it to move. When erosion occurs on a slope, soil is washed from the slope. The steeper the slope, the more erosion can occur. Obstacles like rocks and vegetation can slow the progress of erosion or divert the path of the erosion. 30

Investigation 1 CaCO 3 + 2HCl  CaCl 2 + CO 2 + H 2 O Calcium Hydrochloric Calcium Carbon Water carbonate acid chloride dioxide GAS Marble – consists mostly of the mineral calcium carbonate (CaCO 3 ) 31

32

Mantle Convection and Plate Tectonics 33 Hot mantle rises, cools at surface and sinks. Crust floats on mantle. New crust material comes from rising mantle, pushes old crust away.

Mantle Convection and Plate Tectonics 34

Plate Tectonics Over Geologic Time 35

Wind erosion Sandstone 36 Sand grains carried by strong and consistent winds act as abrasives capable of sculpting solid rock.

Wind erosion Dust Bowl in Texas, Soil erosion in cultivated farmlands can result in devastating dust storms.

Water erosion Cannon Beach, Oregon 38

Water erosion 39

Factors that influence water erosion 40 Rainfall intensity and runoff – heavy bursts of hard rain cause more soil erosion than light rain. Heavy rains can saturate soil and create puddles that flow with gravity and start erosion

Factors that influence water erosion 41 Slope gradient – water erosion is more likely on steeper surfaces, water moves very quickly down the side of a steep hill Vegetation – plant roots can absorb water, hold soil, leaves and branches absorb energy of raindrops

Rock Cycle t/investigations/es0602/es0602page02.cfm Interactive rock cyclehttp:// t/investigations/es0602/es0602page02.cfm 42

Mrs. Degl43 Soil forms from the weathering of the rock below it. The solid rock below is called Bedrock. The rock is exposed to wind, rain etc… The rock breaks down over time to form soil. Soil has different layers called Soil Horizons. O- Horizon = the very thin surface covering (not really a layer) A – Horizon (TOPSOIL) = dark surface soil that contains a lot of living material and dead plant/animal remains (humus). This is the layer with all of the nutrients needed to grow plants. B-Horizon (SUBSOIL) = lighter colored soil with less nutrients and more clay C-Horizon (REGOLITH) = larger rock fragments that sit on top of the unweathered bedrock

Soil Soil is the product of weathering and erosion. 44

What do you see in the soil? 45