GEO 110 Exam 3

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  1. Hawaiian Islands 2. Yellowstone

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  1. Hawaiian Islands 2. Yellowstone

examples of intraplate volcanoes (hotspot volcanoes)

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Hot Spot Volcanoes

form when an area of the mantle melts in the middle of a plate and the magma rises (mantle plume) and collect in the crust

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location of a mantle plume

fixed in place but plate moves over it

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What plate is the Hawaiian Islands on ?

Oceanic plate (1)

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What kind of magma does the Hawaiian Islands have?

basaltic magma = low viscosity (runny)

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What kind of eruptions do the Hawaiian Islands have?

non-explosive eruptions - gentle eruptions of lava flow

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Pahoe-oe

type of Hawaiian island lava flow, warmer and smoother lava

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A-A

type of Hawaiian island lava flow, colder, sharper lava ( painful surface to walk on)

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shield volcanoes

gently-sloping volcanoes that form when the runny lava flows out and spreads laterally

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Hawaiian Volcanoes

chain of volcanoes with NW trend; hot spot fixed in place, but Pacific Plate moves to the NW

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What happens as the Hawaiian volcanoes move to the NW?

All volcanoes form above same hotspot - they become older and inactive as you move NW

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What plate is Yellowstone on?

North American Plate = Continental

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What kind of magma does Yellowstone have?

Rhyolitic Magma - very high viscosity (explosive)

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Is Yellowstone made up of Volcanoes?

No, but large calderas

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What is a caldera?

very large craters formed by collapse of ground surface

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The 3 Calderas of Yellowstone

3 eruptions in last 2 million years

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How long ago was the last eruption of a Yellowstone Caldera?

600,000 years ago

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Is there a Yellowstone eruption to be expected?

Super volcano = new mega eruption to be expected

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huge amount of ash will be all over US

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Long Valley Caldera by Mammoth

Super Volcano, blew up last time was 700,000 years ago

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What are volcanic predictions based on?

  1. Seismicity - many small earthquakes indicate magma is pushing higher

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  1. Gases - Composition changes or increases (sulfur dioxide, CO2

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  1. Ground Deformation - same areas start swelling up when magma is near the surface

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Mass Wasting

downslope motion of Earth material due to gravity

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What is slope stability?

forces acting up a slope

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Driving force or shear stress

drives rocks in to motion = reduces stability

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resisting force or shear strength

works against stress = increases stability

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Shear Stress

depends on slope steepness and weight

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Oversteepening

process that increases slope steepness (may be caused by natural or manmade processes)

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Natural Processes of Oversteepening

wave or river erosion

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Man-made Activities of Oversteepening

road cuts and house building

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by removing lower portion of slope, you remove support for the upper slope

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Road cut

slope is cut to create a flat surface (oversteepening)

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Road fill

material is added to the slope to create a flat surface (added weight)

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Examples of added weight

road fills, houses, large amounts of water

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Water as an added weight

  • can come from rainfall or irrigation

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  • increases the shear stress because it adds weight (water is heavy) which increases gravity

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  • it acts as a lubricant by floating the sediment grains apart - thus reducing friction and favoring motion

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Vegetation as an example of Shear Strength

protects slope from impact of rain

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roots bind sediment grain together

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Small amounts of water as an example of Shear Strength

increases cohesive forces - help keeping sediment grain together

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What are the factors that contribute to mass wasting in Southern California?

  1. dry climate

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  1. wildfires

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  1. sudden, heavy rainfall

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Factor of Safety = FS

Shear Strenghth/ shear stress

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FS could be

1 or >1 or <1

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if FS = 1

stress = not good because things might change in the future; stress might increase

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if FS <1

slope is unstable = stress is greater than strength

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if FS>1

slope is table = strength is greater than stress

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what should the FS be for building purposes?

>1.5

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what are the three types of mass wasting ?

falls, slides, flows

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Falls

rocks separate from steep slope and free fall

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what are the two types of falls?

rockfall and rock avalanche

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Slides

layers slide down slope

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what are the two types of slides?

rock slide and slump

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Flows

earth materials are flowing downhill due to presence of water

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what are the three types of flows?

mudflow/ debris flow

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earth flow

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creep

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where are rock falls common?

common along mountains where it's called = frost (ice) wedging

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what is water's role in rock fall?

when water freezes, it expands thus breaking the rock apart = gravity pull rocks down

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what is an indication that rocks will fall in the future ?

slopes that are formed by the accumulation of rocks that fell from top of cliff

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rock avalanche

large chunks of rocks breaks off at high elevation and falls for hundred of feet

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what happens to the rocks during a rock avalanche?

rocks pulverize, displace air which turns into abrasive dust +air blast

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what are the examples of rock avalanches?

Yosemite, Andes, Alps

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rock slide

sliding occurs on a flat surface between layers

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where does a rock slide occur?

occurs in a slope that is layered

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Example of rock slide

Vajont dam

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rock slide falls into reservoir, creating a huge wave of water that goes over damn, washing town away

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slump

sliding down a curved surface - rotation breaks slope into blocks that are tilted backwards

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why are slumps common?

they are common because of oversteepening

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What are examples of slumps?

Point Ferman (sunken city), San Pedro = wave erosion

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Ocean trails Golf Course ( now trump ), PV = caused by irrigation

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example of slumps

La Conchita (1995) & La Conchita (2005)

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La Conchita 1995

area is unstable because of steep/weak slope, road cut (oversteepening), orchard on top of cliff (irrigation adds water). occurred after rainfall

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La Conchita 2005

debris flow occurs after storms, but water has time to soak into slope leaving top layer dry

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what kind of casualties happened during La Conchita 2005?

many houses were buried and several people re killed

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debris flows/mudflows

usually mixed with a lot of water which moves fast

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examples of debris flows/ mudflows

La Conchita (2005) and Wrightwood, CA,

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Wrightwood, CA

by San Andreas Fault (1940); debris flow was caused by early snowmelt, melted water mixed with loose rocks from frost wedging

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destroyed many houses

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earth flows

less water than debris flows, moves slowly

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What does an earth low start out as?

starts out as a slump; shaped like a tongue or lobe

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Example of earthflow

Portuguese Bend

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Portuguese Bend

very unstable because layers point down towards ocean, oversteepened by wave erosion

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Why would the slop of Portuguese Bend move after rain fall?

lots of clay = expands and becomes slippery; naturally slope would move after rain because of clay or after earthquakes

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Portuguese Bend 1950

more houses and roads are built after area development

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Portuguese Bend 1950 Crenshaw extension

road fill added weight triggers. slump on upper portion and continues downhill as an earthflow

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Besides wave erosion and new area develop what else adds to the earthflow and slumps of the Portuguese Bend?

irrigation of the newly built houses added water which makes earthflow move all the time

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Creep

Affects all slopes due to gravity; slow motion

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Where are creeps the biggest problem?

A problem in cold climate where ground is frozen and then thaw

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Subsidence

sinking; slow and progressive sinking of ground

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natural subsidence

due to compaction of sediment grains in flood plains or river deltas

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example natural subsidence

Mississippi --> New Orleans is below sea level due to subsidence of Mississppi Delta

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Man-made subsidence

result of human activities; pumping of water or oil

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examples of man-made subsidence

Venice, Italy = ground water pumping

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San Joaquin Valley of CA = of 45 feet due to ground water pumping

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Long Beach + caused by oil pumping

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sink holes

sudden collapse of ground surface

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