Weathering, Erosion, Soil and Sedimentary Rocks Chapter 8 & 5

WeatheringWeathering is the breakup of rock caused by exposure to the atmosphere. Climate is the most important factor in controlling the speed of weathering. (Tropical warm/moist) ErosionErosion is break up and transportation of Earth materials by natural agents of H 2 O, wind, or ice.

Mechanical Weathering Disintegration takes place when the composition of the rock is not changed only broken into smaller pieces. Ice wedging-H 2 O expands when it freezes Thermal Expansion-when temperature changes occur. Hydration-continuous wet/dry Exfoliation-the peeling of rock (onion skin) Plant and animal action

Chemical Weathering Decomposition takes place when minerals change into new substances - Basalt into red clay Hydrolysis - dissolved by water Oxidation - corrosion by O 2, ex. Iron minerals into limonite(rust) CO 2 - dissolves minerals into clay Acid Rain - dissolves Calcite (CaCO 3 )

Differential Weathering Not all minerals weather at the same speed. Quartz is most resistant to change, while rocks with calcite weather most rapidly.

Spheroidal Weathering Rocks tend to weather quickly near the edges and corners resulting in rounded boulders.

Soils Climate is the most important factor in developing soils. A warm climate (tropical) with abundant moisture weathers all rock rapidly. Dry cold climates weather rock slowest.

Soil Horizons Soils develop in zones called horizons. Horizon A-a dark upper layer called topsoil. Organic material called humus is a major ingredient. This zone drains well because of high amounts of silt and clay

Horizon B - subsoil with lots of clay. This zone may be rich in minerals washed or leached from the A horizon. Horizon C - this zone is very rocky with weathered fragments of bedrock, it is located on top of un- weathered bedrock.

Horizon A Topsoil Horizon B Subsoil Horizon C Weathered Rock Bedrock

Residual and Transported Soils Soils developed in place from parent material are residual Soils brought in by water, wind or ice are called transported. Loose pieces of rock and gravel are called regolith

Soil Types (climatic) Tropical soils are thick and form in warm rainy climates. Low in fertility but high in organic content. Grassland soils are dark and fertile, rich in loam and organic content. Forest soils have three horizons, high amounts of clay and are infertile.

Soil Types (climatic) Desert soils are thin with high amounts of minerals especially Fe, & CaCO 3. Arctic soils are thin with high amounts of organic materials

Soils

Mass Movement Gravity causes mass wasting. Landslide is sudden movement of rock down slope. Mudflow is down slope movement of saturated soil. Talus is an accumulation of rock at the base of a cliff that is 30 0 or steeper. Creep is slow invisible movement of soil.

Sedimentary Rocks Clastic Sedimentary Rocks consist of fragments glued together with CaCO 3 or SiO 2 Conglomerate- Breccia- Sandstone- Shale-

Breccia Breccia consists of angular pieces of different sizes. Fragments are unsorted. Formed in slides.

Conglomerate Conglomerate rocks consists of rounded fragments. These have traveled in streams. They are unsorted.

Sandstone Sandstone consists of sorted pieces of quartz in layers. Usually formed along shorelines or sand dunes.

Sandstone

Shale Shale consists of fine particles of silt, mud and clay. It forms in deep quiet waters.

Shale

Clastic Sedimentary Rocks Conglomerate Breccia Shale Sandstone

Organic Sedimentary Rocks These rocks consist of living materials like shells, bones, or decayed vegetation. They form in shallow, warm, marine environments.

Fossil Limestone Coquina Chalk all contain organic material

Coquina

Chemical Sedimentary Rocks These rocks are formed by evaporation or precipitation of minerals in arid areas. Rock Salt Rock Gypsum Crystalline Limestone

Rock Gypsum Rock Salt

Where did it form?