Earth Science Review Ch 5 - 6

1. Earth Science Review Ch 5 - 6 Weathering and Mass Movements

2. 5.1 Weathering: Key Concepts • Mechanical weathering occurs when physical forces break rock into smaller and smaller pieces without changing the rock’s mineral composition • In nature, three physical processes are specifically important causes of mechanical weathering: frost wedging, unloading, and biological activity. • Chemical weathering is the transformation of rock into one or more new components. • Two factors that affect the rate of weathering are rock characteristics and climate

3. 5.2 Soil • Soil is the part of the regolith that supports the growth of plants. • Soil has four major components: mineral matter (broken down rock), organic matter or humus (decayed plant material), water and air. • The most important factors in soil formation are parent material, time, climate, organisms, and slope. • Soil varies in composition, texture structure, and color at different depths. Three common types of soil are pedalfer, pedocal, and laterite. • Human activities that remove natural vegetation, such as farming, logging and construction, have greatly accelerated erosion.

4. 5.3 Mass Movements • The transfer of rock and soil downslope due to gravity is called mass movement • Among the factors that commonly trigger mass movements are saturation of surface materials with water, oversteepening of slopes, removal of vegetation, and earthquakes. • Geologists classify mass movements based on the kind of material that moves, how it moves, and the speed of movement.

5. 6.1 Running Water • Water constantly moves among the oceans, the atmosphere, the solid Earth, and the biosphere. This unending circulation of earth’s water supply is the Water Cycle. • Balance in the water cycle means the average annual precipitation over earth equals the amount of water that evaporates. • The ability of a stream to erode and transport materials depends largely upon it’s velocity. • While gradient decreases between a stream’s headwaters and mouth,discharge increases. • Base level is the lowest point to which a stream can erode its channel.

6. 6.2 The Work of Streams • Streams generally erode their channels by dissolving soluble material, by lifting loose particles, and by abrasion or grinding. • Streams transport their load of sediment in three ways: • (1) in solution (dissolved load) • (2) in suspension (suspended load) • (3) scooting or rolling along the bottom (bed load) • Deposition occurs as streamflow drops below critical settling velocity of a certain type of particle size • There are two general types of stream valleys: narrow V-shaped valleys and wide valleys with flat floors.

7. 6.2 The Work of Streams • Most floods are caused by rapid spring snow melt and storms that bring heavy rains over a large region. • Measures to control flooding include the construction of artificial levees, building flood control dams, and placing limits on floodplain development. • A drainage basin is the land that contributes water to a stream.

8. 6.3 Water Beneath the Surface • Much of the water in soil seeps downward until it reaches the zone of saturation. The zone of saturation is where water fills all of the open spaces in sediment and rock. Groundwateris the water within this zone. • Groundwater moves by twisting and turning through interconnected small openings. The groundwater moves more slowlywhen the pore spaces are smaller. • A springforms whenever the water table intersects the ground surface.

9. 6.3 Water Beneath the Surface • Overuse and contamination threatens groundwater supplies in some areas. • Erosionforms most caverns at or below the water table in the zone of saturation. • Karstareas typically have irregular terrain, with many depressions called sinkholes.