Geology Exam #4 Questions With Answers
What is a parent isotope? A daughter?
Parent Isotope: An isotope that undergoes decay to form a daughter isotope
Daughter Isotope: May be stable or may decay to form another daughter (formed from the parent isotope)
What is a half‐life?
The time req...
Geology Exam #4 Questions With Answers
What is a parent isotope? A daughter?
Parent Isotope: An isotope that undergoes decay to form a daughter isotope
Daughter Isotope: May be stable or may decay to form another daughter (formed from the parent
isotope)
What is a half‐life?
The time required for 1/2 of a radioactive isotope to decay ion a stable daughter isotope
What is meant by mass wasting?
The general term for all gravity induced movement of material down a slope.
How are the different mass wasting events subdivided?
Subdivided by the type of motion, type of material, and speed of motion
What is the angle of repose? What are the different factors which control this angle?
Angle of Repose: Maximum slope that loose, unconsolidated material can have
- Depends on the size of particles, shape of particles, and water competent
What are the possible triggers of mass wasting events?
The angle of repose (due to gravity) and "stupid human tricks"
What are the different mass wasting events and how do they differ?
Landslides, creeps, slumps, rock avalanche, debris avalanche, mudflows, and rock falls
What's groundwater?
Precipitation that enters the subsurface through infiltration
How is water distributed on the planet?
Water is distributed in freshwater and saltwater
- 95.96% is in the ocean
- 4.04% is fresh water
How does water enter into the subsurface?
Through the process of infiltration which is dependent on porosity and permeability
What is porosity? Permeability?
Porosity: Percentage of rock/sediment that consists of voids and openings
Permeability: Ability of rock/sediment to allow a fluid to pass through it
What is an aquifer? An aquiclude? An aquitard?
Aquifer: A material that is both porous and permeable
Aquiclude: A material that is nonporous and/or impermeable
Aquitard: Doesn't stop the fluid from passing through, just slows it down
,How does a confined aquifer differ from an unconfined aquifer?
Confined aquifer: In the middle of lesser permeable rock or clay, and can build up additional pressure.
When the pressure they build up exceeds the ground elevation, they are considered artesian and
water will flow without pumping (as in a spring) at the grounds surface.
Unconfined aquifer: Extend from the water table to the base of the aquifer, represented by an
impermeable boundary. Most of the unconfined aquifers are formed by highly permeable layers
(gravel, coarse or medium sand) and less permeable formations (silt or clay)
What is the water table? The vadose zone? The phreatic zone? The capillary fringe?
Water table: The level below which the ground is saturated with water
Vadose zone: The unsaturated zone right beneath the ground
Phreatic zone: The saturated zone underneath the water table
The capillary fringe: The zone of soil immediately above the water table
What is a 'perched' water table?
When the water table reaches the Earth's surface
How is water withdrawn from the subsurface?
By drilling up a well and pumping the water out:
- Water in well, rises to the top of the water table
- Water beneath the surface moves slowly (a few cm/m per day) depending on permeability
- If water is extracted too fast, the water table will drop locally around the well called the "cone of
depression"
What is an 'artesian well'?
A confined aquifer containing groundwater under high pressure. This causes the water level in a well
to rise to a point where hydrostatic equilibrium has been reached.
How do springs form?
Where the aquifer surface meets the ground surface.
What are some of the effects of excessive groundwater withdrawal?
- Drying up of lakes and streams
- Killing off vegetation (thus creating mass wasting)
- Ground subsidence (San Joaquin dropped 30 ft in 52 years)
What is the major consumer of groundwater?
Irrigation
How is groundwater contaminated?
Road salt, toxic substances from mining sites, and used motor oil
What are losing streams and gaining streams?
Losing streams: It "loses" water to the saturated zone. Also called the "influent stream".
Gaining streams: It "gains" water from the saturated zone. The water table emerges above the ground
along a gaining stream. Also called the "effluent stream".
, What is karst topography?
Any region where the terrain has been dissolved by the physical and chemical weathering of the
bedrock.
How do caves form?
The dissolution of limestone. Rainwater picks up carbon dioxide from the air and as it percolates
through the soil, which turns into a weak acid. This slowly dissolves out the limestone along the joints,
bedding planes and fractures, some of which become enlarged enough to form caves.
- Dissolved by the physical/chemical weathering of bedrock (a.k.a karst topography)
The term half life represents the time it takes for..
For half of the parent atoms to decay into daughter atoms.
1000 atoms of a radioactive parent atom decays but contains 250 atoms. It's 1/2 life is 1 million. How
old is the rock?
2 million years old
12.5% K40 and 87.5% Ar40. Half life for the reaction of K40 to decay to Ar40 is 1.25 billion years old.
How old is the rock?
3.75 billion years
75% U235 and 25% Pb207. The half life is 4.5 billion years. How old is the rock?
2.25 billion years
The process by which masses of rock and soil move downhill under the influence of gravity is
______________.
Mass wasting
How do geologists classify mass movements?
By the SPEED of the movement, the NATURE of the movement and the NATURE of the material.
What is a creep? A flow?
Creep: Very slow, downhill movement of soil (1 cm/year); when tree trunks are tilted
Flow: When motion is taking place within a moving mass of unconsolidated material
Which is NOT an important factor in causing mass movements?
a. Shape of particle
b. Size of particle
c. Temperature of particle
d. Water competent
c. Temperature of particle
Which is true?
a. Coarse sand form steeper slopes that fine grain sand
b. Angular pebbles form steeper slopes than coarse sand
c. Round debris form steeper slopes than angular pebbles
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