Chapter 21 Section 4 Pages
W.E.D.S 1. Weathering a. Physical b. Chemical 2. Erosion 3. Deposition 4. Sedimentation (burial & compaction)
1. Weathering The physical and chemical processes by which rocks are broken down into smaller pieces. Rocks are broken down by the effects of weather. It is the “prepping” process of erosion.
4 Factors that effect the rate of weathering: 1.Surface Area (exposure) - Exposing more surface area will increase the rate of weathering. 1.Particle Size – Larger particles weather slower and smaller particles weather at a faster rate. 1.Chemical Composition (what a rock is made of) – Certain rocks and minerals are naturally weaker than others, while others are more resistant (stronger). 1.Climate – Warmer, moister climates have the most weathering. Heat & Water speed up all chemical reactions. This is the most important factor in weathering.
Physical Weathering Physical weathering occurs when physical forces break rock into smaller and smaller pieces without changing the rocks mineral composition. These forces are wind, water, waves, and gravity.
Wind Fast moving wind will carry fine, dry sediment over long distances
Water most effective weathering agent shapes the Earth’s surface Streams-- Flowing water will lift and carry small sediments such as silt and sand.
Waves/Oceans Tidal action and waves carry away weathered material Narragansett Town Beach RI
Gravity When sediments are weathered they may be transported downward by gravity. The general term for this is mass movement.
Chemical weathering Chemical weathering is the breakdown of rock into smaller pieces by chemical processes. Rocks are broken down by chemical reactions within the environment. Rocks can weaken, decompose or dissolve. The chemical composition of the rock changes.
Oxygen When elements react with Oxygen, their properties change. Iron combines with oxygen in the presence of water rust
Carbon Dioxide Carbon Dioxide reacts with water and forms carbonic acid (slightly acidic). Minerals dissolved by carbonic acid may be washed away, leaving underground pockets, or caves.
Water Water weathers rock by dissolving it. Almost all chemical weathering reactions take place in the presence of water. Some minerals react with water which change their physical properties-----hydrolysis Minerals often dissolve in water and are carried away to lower layers of rock. This process is called leaching.
Acid Precipitation Sulfur dioxide and nitrogen oxides enter the air as a result of burning fossil fuels (coal, oil, gas). These chemicals (pollutants) can react with water in the air, forming sulfuric acid, nitric acid, or nitrous acid. When this happens, precipitation is acidic and causes damage to organic and inorganic matter.
2. Erosion The removal and transportation of weathered and nonweathered materials in the landscape from one location to another. The process by which water, wind or gravity moves fragments of rock and soil. – Water—(running & underground)— most effective physical agent of erosion
Human Erosion 1. Deforestation:– the clearing of trees from an area without replacing them. Speeds up erosion. 2. Construction – the clearing of land to build buildings/houses also causes all loose soil to erode away.
3. Deposition Where water moves more swiftly there will be more erosion Where the water slows down sediments will be deposited
Glaciers Glacial ice drags rocky material that scours the surface it flows over. Melted water carries sediment away from the glacier.
Mass Movements Landslides Mud flows Creep La Conchita, CA-1995
4. Sedimentation Soil/silt/sediment is deposited and: Compacted: pressed together Layered: variety of silt, sediment, clay, soil, pebbles, fossils Cemented: large and small combined to form solid
W.E.D.S 1. Weathering a. Physical b. Chemical 2. Erosion 3. Deposition 4. Sedimentation (burial & compaction)