Mass Movements & Water flow Chapter 5 Mass Movements & Water flow

5.3 Mass Movements Triggers of 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 Water: saturation of surface materials with water decreases friction. Slopes: Steepening of slopes unstabilizes angles Removal of vegetation: Loosens soil Earthquakes: Destabilizes rock

5.3 Mass Movements Types of Mass Movements  Geologists classify mass movements based on the kind of material that moves, how it moves, and the speed of movement.  Rockfalls • They occur when rocks or rock fragments fall freely through the air. • Common on steep slopes. • Result from mechanical weathering of rocks caused by freeze-thaw cycles or plant roots.

5.3 Mass Movements  Slides  Slumps Types of Mass Movements Block of material moves suddenly along a flat, incline surface on a slide. Slides that include segments of bedrock are called rockslides. Fastest mass movements. Triggered by rain or melting snow.  Slumps The downward movement of a block of material along a curved surface. Does not travel very fast. Leave a crescent shaped cliff just above the slump

Heavy Rains Can Trigger Slumps

5.3 Mass Movements Types of Mass Movements  Flows • Flows are mass movements of material containing a large amount of water. • Mudflows move quickly and carry a mixture of soil, rock, and water that has a consistency of wet concrete. • Earthflows move relatively slowly and carry clay-rich sediment.

5.3 Mass Movements Types of Mass Movements  Creep The slowest type of movement is a creep. Only travels a few mm or cm per year. Freezing expands the water in soil, lifting soil particles at right angles to the slope. Thawing cause contraction, which allows the particle to fall back slightly to lower level. This cycle moves the particles a short distance down hill.

Creep

6.1 Running Water The Water Cycle  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.

6.1 Running Water The Water Cycle  Processes involved in the cycle are • precipitation • evaporation • infiltration—the movement of surface water into rock or soil through cracks and pore spaces • runoff • transpiration—the release of water into the atmosphere from plants through the ground

The Water Cycle Makes no sense without caption in book

Distribution of Earth’s Water

6.1 Running Water Earth’s Water Balance  Balance in the water cycle means the average annual precipitation over Earth equals the amount of water that evaporates.

6.1 Running Water Streamflow  The ability of a stream to erode and transport materials depends largely on its velocity. • Gradient is the slope or steepness of a stream channel.

6.1 Running Water Streamflow is the ability of a stream to erode and transport materials depends largely on Velocity, which is the distance the water travels in a period of time. Gradient is the slope/steepness of a stream channel. The steeper the gradient, the more energy the stream has as it flows downhill. The stream channel is the course the water in a stream follows. water in a smooth channel flows more easily Larger channels have more efficient water flows because a less of the water is in contact with the channel surfaces (less friction). The discharge of a stream is the volume of water flowing past a certain point in a given unit of time. This can change with rainfall and snowmelt Change is discharge can change the size & velocity of a stream.

6.1 Running Water Changes from Upstream to Downstream  While gradient decreases between a stream’s headwaters and mouth, discharge increases.

6.1 Running Water Changes from Upstream to Downstream • A tributary is a stream that empties into another stream. • Factors that increase downstream - velocity - discharge - channel size

Sea Level and Streams

6.1 Running Water Changes from Upstream to Downstream • Factors that decrease downstream include - gradient, or slope - channel roughness

Rivers with Many Meanders

6.1 Running Water Changes from Upstream to Downstream  Base Level • Lowest point to which a stream can erode • Two general types - ultimate—sea level - temporary, or local • A stream in a broad, flat-bottomed valley that is near its base level often develops a course with many bends called meanders.