Geology Final Exam - Mass Wasting, Running Water, & Groundwater
What is the difference between a cut bank and a point bar?
A cut bank is on the outside of a meander, where erosion occurs A point bar is on the inside of a meander, where deposition occurs
What is the difference between an antecedent and diverted stream?
An antecedent stream existed before current topography, a diverted stream was redirected by topography
What is a floodplain?
An area of low relief lying adjacent to a river, floods with excessive discharge
What is subsidence?
An effect of depletion that causes the land to sink
What is base level and ultimate base level?
Base level is a local lake or large body of water that limits erosion Ultimate base level is the ocean
What are the four basin patterns?
Dendritic: develops on relatively uniform surface material Radial: develops on isolated volcano cones or domes Rectangular: develops on highly jointed bedrock Trellis: develops an alternating weak and resistant bedrock
Who was Henri Darcy?
Discovered the relationship between the slope of the water table, permeability, and how it affects well productivity
What are the speeds of mass wasting from quickest to slowest?
Fall, slide, flow, slump, creep
What are the types of flooding?
Flash floods, riverine floods, ice dam floods, failure floods Flash floods occur in small streams, riverine floods occur in large streams
What is a superposed stream?
Formed on overlying topography and altered it (forms water gaps)
What is an alluvial fan?
Forms when sediment-laden water enters a dry valley
Identify percentage distribution of freshwater on Earth:
Glaciers and ice sheets: 68.6% Groundwater: 30.1% Surface water: 1.3%
What is the main cause of mass wasting?
Gravity
What is a common misconception about groundwater?
Groundwater does not exist in channeled flow, it flows through rock pores and inbetween grains
How do rivers change based on the gradient?
Higher gradient and farther from base level typically results in narrow, V-shaped valleys that cut downwards Lower gradient and closet to base level typically results in wider, flat bottomed valleys that cut sideways
What affects the angle of repose?
Material size: coarse material will have a steeper angle than fine-grained Saturation: small amounts of water can create cohesion, too much will completely saturate the sediment
Explain creep mass wasting:
Most damaging and slowest type, involves grains freezing and expanding, then thawing moving slightly downward Occurs over long periods
What is Karst topography?
Named after a plateau in Slovenia with sinkholes and caves, refers to other areas with such topography Occurs in humid regions with carbonate bedrock Rain + carbon dioxide = carbonic acid, which dissolves limestone and dolostone
What are three examples of mass wasting events?
Northwestern Wyoming in 1925 Italian Alps in 1963 causes dam flooding La Conchita, California when houses were constructed on top of loose material
Identify percentage distribution of water on Earth:
Oceans: 96.5% Freshwater: 2.5% Saline lakes and groundwater: 1%
What are river terraces?
Old floodplains that were stranded at higher level as sediments were deposited
What is the difference between porosity and permeability?
Porosity is the amount of pore space a material has, permeability is how easily the water can actually pass through - relates to the alignment of pores
What is primary vs secondary porosity?
Primary porosity refers to pores that develop during deposition and lithification, secondary porosity refers to pores that develop after the rock forms
How does saltwater encroachment occur?
Pumping of a well near coasts, where the fresh groundwater lies above the saline water, can result in the ascension of the underlying saline water and cause it to be pumped by the well
What other factors affect mass wasting?
Rainfall, earthquakes, human activity
How do you calculate slope of a river?
Relief divided by horizontal distance A waterfall has undefined slope
What are the two water dispute arguments?
Riparian rights: all who border water have rights to that water Prior appropriation: first come, first served
How does groundwater contamination occur?
Septic tanks can leak and the contaminated water can mix with the groundwater Permeable material is able to filter out the contaminants A well can also change the flow direction to prevent the contaminants from mixing, or it could do the opposite and pull in more contaminants Contamination is a bigger issue for groundwater than surface water
What are methods to prevent mass wasting?
Simply being aware of where houses are being constructed Building houses on terraces rather than a hill Using retaining walls to stop debris Putting rock belts in joints
What is the difference between the aeration zone and the vadose zone?
The aeration zone is the upper zone of soil that is not saturated and the vadose zone is the lower zone that is saturated with water The water table divides the two
What affects the level of the water table?
The amount of precipitation, local topography, and water usage by humans Excessive pumping can cause water table depletion
What is the angle of repose?
The angle at which an unconsolidated pile of sediment is stable
What is the discharge rate versus the recharge rate?
The discharge rate is 600-900 mm/year, the recharge rate is only about 5 mm/year
What is incised meandering?
The downward erosion of rivers, rather than sideways that occurs due to response from rejuvenation
How are looping flow lines created?
The downward pull of gravity and the tendency of groundwater to move toward areas of reduced pressure
What is the 100th Meridian?
The line that divides the United States - western of it gets little rain, eastern gets much more
What is a drainage basin?
The network of land that contributes water to a stream Smaller basins combine into bigger basins Separated by divides
What is discharge?
The volume of water per unit of time in a stream
How can a drainage basin change?
Upstream development: changes in runoff and wetlands, can alter the capacity of a basin Downstream restrictions: dams and levees can alter the capacity of a basin Urbanization decreases lag time
What is a braided stream?
When a stream has more sediment than it can carry
What are perched water tables?
When an aquitard creates a small reservoir of water above the water table Creates issues and confusion for well drillers
What is a delta?
When sediment-laden water enters a larger body of water Extend over time and move when the sediment pile becomes too large
Where do springs occur?
Where the water table intersects the Earth's surface
