Weathering
Weathering the process that produces change in the surface of rocks exposed to the atmosphere and/or hydrosphere.
Two Types OF Weathering: Physical weathering is breaking rock by force. ex: hitting, scratching, cracking Chemical weathering is where the rock material is changed into another substance by reacting with a chemical.
Frost action (ice wedging)- Water seeps into small cracks in rocks. When the water freezes it expands creating great pressure. The crack widens and allows water to seep deeper into the rock.
Biological Activity Plant action- Tiny root hairs seek out small cracks and pits in rock. Once the root hairs find a place they grow and expand. The expansion causes great pressure and cracks the rock.
Unloaded Exfoliation Rocks formed deep in the Earth are made under high pressure. When the pressure is released the rocks expand & crack. May also be caused by alternate heating and cooling of rocks by weather conditions.
Chemical Weathering Oxidation- Oxygen in the atmosphere chemically reacts with minerals. ex.: rusting of a nail Water **** MOST IMPORTANT !!!!! Minerals are dissolved in water. ex.: Halite, calcite
Acid- Carbonic acid: C02 dissolves in rain water forming a weak acid Acid Rain: Sulfur Dioxide in the atmosphere dissolves in rain water forming a strong acid (sulfuric acid).
Chemical Weathering
Chemical Weathering
Ex. Of Chemical Weathering
Rates of weathering will be influenced by: Surface area exposed - weathering occurs on the surface. More surface exposed, the faster the weathering will occur.
A smashed piece has greatest surface area exposed A smashed piece has greatest surface area exposed. The interior can now be attacked. A full, solid block has the least surface area. The interior is safe from exposure.
Rates of Weathering will depend on: Mineral composition- some minerals are more resistant than others. ex.:Quartz is resistant to chemical and physical weathering.
Rates of Weathering will depend on: Climatic Conditions: Cold and/or dry climates favor physical weathering. Warm and wet climates favor chemical weathering. Frost action works best in areas where the temperature fluctuates wildly.
Soil - The product of weathering Soil- rocks, minerals (mainly sand and clay), and organic material (regolith and organic matter) Soil forms layers of different characteristics called horizons.
What are the main components of soil? Mineral Matter Air Water Organic Matter
What are the FACTORS that make SOIL? TIME 1000’S TO 10,000’S OF YEARS LAY OF THE LAND / “SLOPE” TOPOGRAPHY LIVING ORGANISMS ANIMALS AND PLANTS CLIMATE HOT/COLD, WIND/RAIN PARENT MATERIAL ROCKS AND MINERALS
Topography Physical land features
Why is soil important ? Necessary for the growth of rooted plants which support our life system !!!!
Erosion Movement of sediments (soil) from one location and deposition of it another place. Can occur in 2 ways
2 ways erosion can occur …. Earth processes which move material on the Earth’s surface over long periods of time, such as weathering and gravity Human activity which moves material on the Earth's surface over short periods
Transport Agents of Erosion Water Rain Streams and rivers Ocean Ice (glaciers) Wind Gravity
Rain drop erosion
Erosion by Water
Rill Erosion
Erosion by Wind
Erosion due to gravity
Example of Human Made Erosion
Erosion at Construction Site
Silt fencing during construction doesn’t necessarily stop all erosion
Vegetation protects soil
My Neighbor has my soil!
How Erosion Effects the Environment
#1 Pollutant to our Waters
Sedimentation in Rivers pollutes water with soil particles damages water ecosystems through reduced sunlight for aquatic plants and animals increases water treatment costs for human water consumption reduces the depth of rivers, thus creating waterways that can't be navigated by commercial crafts
Wind Erosion removed topsoil
Removal of topsoil from land areas prevents plant growth alters ecosystems, thus reducing the biodiversity of life destroys crops reduces agricultural food production reduces farming income
The Great Dust Bowl Wind Erosion
Wind Erosion increases the amount of particles in the air reduces visibility reduces air quality causes breathing problems (asthma, etc.)
What can help prevent erosion?
Plants can help prevent erosion. Look at the roots on these grasses Plants can help prevent erosion! Look at the roots on these grasses. Roots help hold the soil in place so that it doesn’t wash away. Plant roots
Mass Movement The transfer of rock and soil downslope due to gravity
Triggers of Mass Movement Saturation of material with water Oversteepened slopes Removal of vegetation Earthquakes
Types of Mass Movements Based on: Kind of material that moves How it moves Speed of movement
Rockfalls Usually happens on oversteepened slopes due to mechanical weathering (freeze-thaw)
Slides Occur suddenly and can reach speeds of over 200 km/hr Usually occur in the mountains
Slumps Do not occur suddenly Usually happens in clay soil
Flows Contains a large amount of water Mudflows – move quickly Earthflows - slower
Creeps Occur gradually over time Usually due to freezing and thawing of soil
The End Chapter 5