GEO 110 Exam 3

1. Hawaiian Islands 2. Yellowstone

examples of intraplate volcanoes (hotspot volcanoes)

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

location of a mantle plume

fixed in place but plate moves over it

What plate is the Hawaiian Islands on ?

Oceanic plate (1)

What kind of magma does the Hawaiian Islands have?

basaltic magma \= low viscosity (runny)

What kind of eruptions do the Hawaiian Islands have?

non-explosive eruptions - gentle eruptions of lava flow

Pahoe-oe

type of Hawaiian island lava flow, warmer and smoother lava

A-A

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

shield volcanoes

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

Hawaiian Volcanoes

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

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

What plate is Yellowstone on?

North American Plate \= Continental

What kind of magma does Yellowstone have?

Rhyolitic Magma - very high viscosity (explosive)

Is Yellowstone made up of Volcanoes?

No, but large calderas

What is a caldera?

very large craters formed by collapse of ground surface

The 3 Calderas of Yellowstone

3 eruptions in last 2 million years

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

600,000 years ago

Is there a Yellowstone eruption to be expected?

Super volcano \= new mega eruption to be expected

huge amount of ash will be all over US

Long Valley Caldera by Mammoth

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

What are volcanic predictions based on?

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

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

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

Mass Wasting

downslope motion of Earth material due to gravity

What is slope stability?

forces acting up a slope

Driving force or shear stress

drives rocks in to motion \= reduces stability

resisting force or shear strength

works against stress \= increases stability

Shear Stress

depends on slope steepness and weight

Oversteepening

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

Natural Processes of Oversteepening

wave or river erosion

Man-made Activities of Oversteepening

road cuts and house building

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

Road cut

slope is cut to create a flat surface (oversteepening)

Road fill

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

Examples of added weight

road fills, houses, large amounts of water

Water as an added weight

- can come from rainfall or irrigation

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

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

Vegetation as an example of Shear Strength

protects slope from impact of rain

roots bind sediment grain together

Small amounts of water as an example of Shear Strength

increases cohesive forces - help keeping sediment grain together

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

1. dry climate

2. wildfires

3. sudden, heavy rainfall

Factor of Safety \= FS

Shear Strenghth/ shear stress

FS could be

1 or \>1 or

if FS \= 1

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

if FS

slope is unstable \= stress is greater than strength

if FS\>1

slope is table \= strength is greater than stress

what should the FS be for building purposes?

\>1.5

what are the three types of mass wasting ?

falls, slides, flows

Falls

rocks separate from steep slope and free fall

what are the two types of falls?

rockfall and rock avalanche

Slides

layers slide down slope

what are the two types of slides?

rock slide and slump

Flows

earth materials are flowing downhill due to presence of water

what are the three types of flows?

mudflow/ debris flow

earth flow

creep

where are rock falls common?

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

what is water's role in rock fall?

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

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

rock avalanche

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

what happens to the rocks during a rock avalanche?

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

what are the examples of rock avalanches?

Yosemite, Andes, Alps

rock slide

sliding occurs on a flat surface between layers

where does a rock slide occur?

occurs in a slope that is layered

Example of rock slide

Vajont dam

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

slump

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

why are slumps common?

they are common because of oversteepening

What are examples of slumps?

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

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

example of slumps

La Conchita (1995) & La Conchita (2005)

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

La Conchita 2005

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

what kind of casualties happened during La Conchita 2005?

many houses were buried and several people re killed

debris flows/mudflows

usually mixed with a lot of water which moves fast

examples of debris flows/ mudflows

La Conchita (2005) and Wrightwood, CA,

Wrightwood, CA

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

destroyed many houses

earth flows

less water than debris flows, moves slowly

What does an earth low start out as?

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

Example of earthflow

Portuguese Bend

Portuguese Bend

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

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

Portuguese Bend 1950

more houses and roads are built after area development

Portuguese Bend 1950 Crenshaw extension

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

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

Creep

Affects all slopes due to gravity; slow motion

Where are creeps the biggest problem?

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

Subsidence

sinking; slow and progressive sinking of ground

natural subsidence

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

example natural subsidence

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

Man-made subsidence

result of human activities; pumping of water or oil

examples of man-made subsidence

Venice, Italy \= ground water pumping

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

Long Beach + caused by oil pumping

sink holes

sudden collapse of ground surface