Final Exam Flashcards
controlling force of mass wasting
gravity
the important factors in mass wasting
earth material, water content, slope
• Consolidated material (tightly arranged sediment) will not waste as easily s unconsolidated (loosely arranged sediment)
• Oversaturation of water content will lubricate the sediment and cause the sediment to be very loosely attached
Saturation will cement the sediment together and cause it to be tightly attached
No saturation will cause the sediment to be loosely attached.
Think of this with sand and building a sand castle.
types and rates of movement
- Creep – very slow
- Slump – relatively slow
- Avalanche – very brief and extremely rapid
- Mud Flow – ~100mph, very rapid
Creep
very slow wasting, it is the downward progression of rock/soil down a gradient caused by gravity
Slump
form of mass wasting that looks like stair steps on a hill. Caused by movement of loose sediment by earthquakes shocks, wetting, and freezing.
Avalanche
sudden and drastic flow of snow down a slope caused by loading of new snow (causing too much weight) or an earthquake.
Mud Flow
very rapid movement of loose soil and water down a gradient, caused by over saturation of sediment, flooding, and eruptions.
Rock Slides
can happen due to erosion of the base of a cliff over time eventually causing the top part of the cliff to topple due to its unstable nature
Debris flow and debris avalanche
Debris flow and debris avalanche are similar to mudflow / avalanche just with different sediment. Rockfalls and debris falls form a pile of debris that pile up to form a talus under a cliff
effects of deforestation on mass wasting
• Deforistation causes the sediment to be less consolidated (causing the sediment to become loose) which can increase the risk of mass wasting events.
difference in stability for rock layers – beds parallel a valley slope and those beds which dip into the valley wall.
- Beds that are parallel to a valley slope become a potential slip surface which can cause mass wasting, especially when water saturates the area between the valley’s sedimentary rock layer and the bedrock.
- Beds that dip into the valley wall will not slip along the bedrock.
• Think about the surface of wood with the grain and then against the grain, with the grain it’s much more slick (bed parallel to a valley slope), against the grain it’s not slippery (bed dips into a valley wall).
What are the triggers for mass wasting? Can human activity trigger mass wasting? How?
- Triggers of mass wasting include; earthquakes, flooding/wetting, freezing of water in sediment, animal activity, etc.
- Humans can trigger mass wasting in many different ways including; removal of vegetation, increasing angles of slopes, addition/removal of water, etc.
➢ How do rivers and streams fit into the hydrologic cycle (run off verses infiltration)? What are the different water reservoirs? Be able to place them in order from largest to smallest.
- Rivers and streams fit into the hydrologic cycle (the water cycle) because they transport water. Infiltration is where water on the ground surface enters the soil, run-off is when the soil is saturated to full capacity due to infiltration and any additional water flows over land (creating rivers and streams). Run-offs are the primary agent in all water erosion.
- Rivers and streams transport their run-off water to water reservoirs such as lakes and oceans. Oceans obviously the largest.
How are materials transported in rivers and streams?
Through the force of the water’s current. The higher the velocity of a current the larger the sediment a stream/river can transport.
What are stream divides and drainage basins?
A drainage basin is the extent of an area where all the run-off water converges to a single point (such as a single river, lake, ocean, etc).
Be able to recognize the difference between stream channel types
straight, meandering, braided
• Also remember that braided streams can move the most sediment / water the quickest (he’s stressed this in lecture). The point bar is deposited sediment on a meandering stream (the sediment deposits because the stream’s current slows down around the sides). The cut bank is eroded land from water erosion. (you will need to know cut bank and point bar).
the different stream drainage patterns and what each tells you about the underlying rocks
- Meandering channel forms on low slopes through easily eroded bedrock.
- Dendritic has flat lying layers / bedrock
- Trellis has folded rock layers.
- Rectangular drainage has joints and faults
- Radial drainage occurs on high mountain peaks or volcanoes.
➢ Describe how velocity changes within a meandering stream. How does this lead to the formation of point bars and cut banks? How do meandering streams change over time?
- Velocity is fastest in the middle of meandering streams and slows down around the edges. Point bars are formed on the edges of streams where the velocity of water slows down enough to where sediment can be deposited, cut banks form from the erosion of the land from the water.
- Meandering streams change from (youthful) → (mature) → (old age) over time.
- Youthful streams have a narrow channel width.
- Mature streams have a wide channel length (due to erosion).
- Old age streams have an even wider channel length and are represented by oxbow lakes which are essentially scars in the sediment where the meandering stream use to run.