– Mixture of hot rock fragments and gasses that pours at a high velocity down the flank of a volcano- Dry flow- Occurs in composite volcanoes (andesite and rhyolite) – Moves at high speeds (100 – 200 mph)- Occurs at convergent plate boundaries (subduction zones)-Initiated by dome eruption or collapse-Very destructive-Ex: Soufriere Hills, Montserrat, 1997;
– Volcanic mudflow- Follow large pyroclastic eruptions- Rapidly flowing mixture of pyroclastics and water- Originate from the melting of ice, rainfall, or the breakout of a lake- Ex: Mt.
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St Helens 1980
Pyroclastic Flow Eruptions
– Mt. Vesuvius, 79 AD- Mt. Pelee on Martinique, 1902- Mt. St Helens, 1980-Mt. Pinataubo,Phillipines, 1991
– Nevado Del Ruiz, 1985- Mt. Pinatubo, 1991- Mt.
St Helens- Possibly Mt. Rainer
What are the three ways to melt rock?
– Increase temperature- Decrease pressure- Add water
Mt. Mazazma/Crater Lake
– Subduction zone in ROF- Cascades- Mt. Mazama collapsed to produce Crater Lake- 42 x larger eruption then St. Helens
– Subduction Zone in ROF- Cascades- Erupted 3 times in last 30 years
– Subduction in ROF- Mexico- Danger to Mexico City- 20 million people live close enough to be affected
Nevada del Ruiz,Columbia South America, 1985
– Subduction in ROF- Columbia/ South America- City destroyed by lahar, evacuation called off- new respect for fire and ice combination (deadly!)
– Subduction in ROF- Indian Ocean/ Indonesia- generated 120 ft tsunami
– Subduction in ROF- Indonesia- largest eruption in historic time- began global cooling, 1816- “year without a summer”
Mt. Pinatubo, 1991
– Subduction in ROF- Phillipines- Plinian eruption- Caused global cooling- Pyroclastic flow
Mt. Pelee, 1902
– Subduction OUTSIDE the ROF- Martinique, Caribbean- Pyroclastic flow destroyed town- Only 1 survivor
– Subduction OUTSIDE the ROF- Montserrat, Caribbean- Most active volcano in Caribbean and anywhere- Pyroclastic flows (forced evacuation of southern half of island and destroyed capital of Plymouth)- Possibly next Krakatau
What are other possible Tsunami events that could occur in the Pacific Ocean and Atlantic Ocean?
– Submarine landslides could cause a tsumani (Hilnia Slump in Hawaii, Big Island)- Landslides around canary Island- Mega tsumani, volcano could cause 300 ft wave to Europe
Turkey (Izmit), 1999
– Earthquake event- Continental Transform plate boundary- Main hazard: structural damage and tsunami- 7.4 magnitude
i) Transform plate boundaryii) Collapse of structures is main cause of deathiii) Fifth most deadly earthquake of that magnitudeiv) rupture search reveals no recent break in probable scarp
San Fransisco, 1906
i) Magnitude 7.1ii) Ground rupture was 265 miles longiii) Extensive firesiv) Epicenter was on the SAF
Loma Prieta, 1989
– Mag 7.1- event in the bay area- liquefaction and fire- epicenter on SAF in mountains- great earthquake- Last large earthquake
– Occurred on a blind thrust fault, NOT SAF- Not on Plate Boundary
New Madrid, 1811,1812
– In the middle of US- 8.0 mag- Great earthquake
(1) Was predicted(2) Evacuation was made(3) 7.3 Earthquake
Tangshan, China, 1976
(1) 7.6 magnitude(2) Not on a plate boundary(3) 93 percent of all homes destroyed
i) 9.2 subduction earthquakeii) Largest US earthquakeiii) Tsunami wave traveled to Northern CA iv) Extensive ground rupturev) landslidesvi) liquefactionvii) subduction event with major tsunamiviii) Ring of fire
Mexico City, 1985
i) Subduction eventii) In Ring of Fireiii) 250 miles from epicenteriv) Town built on ancient lake bed which amplified the seismic wavesv) Collapsed buildings due to resonancevi) Not on a plate boundary
i) Ring of fireii) 9.5 subduction zone earthquakeiii) Largest earthquake recordediv) Tsunami traveled to Hawaii and japan v) Subduction events with major tsunami
Tokyo, Japan, 1923
i) Subduction eventii) In Ring of Fireiii) Fire was worst hazard
Kobe, Japan, 1995
i) Subduction eventii) In Ring of Fireiii) Most recent devastating earthquake in japaniv) Liquefactionv) Firevi) Most expensive natural disaster yet
i) Subduction event with major tsunamiii) Ring of fireiii) Megathrust earthquake
i) Continent- Continent Convergent plate boundaryii) Bam Iran- 90 percent of building destroyed because adobe structures iii) Has had many devastating earthquakes
i) Continent-Continent Convergent plate boundaryii) Massive deaths and destructioniii) Almost entire towns had vanishediv) 7.6 magnitude
Sichuan, China, 2008
7.9occured on reverse fault- not on plate boundarylandlside
What are the 2 types of body waves?
P waves and S waves
– Primary Waves- compressional waves- Felt first, fastest, in a push-pull manner (like a slinky)
– Secondary Waves, shear waves- Move in a up and down motion- Does not travel threw fluid
Long L waves
c) Long L wavesi) Travel near surface after P and S waves strikeii) Slower then body waveiii) Low frequency wavesiv) Cause most of the damagev) Love waves- side to side motion, don’t travel through watervi) Rayleigh waves- rolling waves, vertical and horizontal shaking
How do P and S waves help us understand Earth’s internal structure?
– Show the travel path and velocities which can be analyzed to show earths inner structure
– measure of energy released during an earthquake
– Ml, measures largest amplitude on seismogram- Logarithmic scale (5 is 10x stronger then a 4 and 100x stringer than a 3)- Ground shaking is 10 times worse for each unit on a scale
Moment Magnitude scales (Mw)
Newer scale, more reliable for large magnitude earthquake(2) Measures strength of rock, rupture area along fault plane or subduction zone, displacement, slip, or offset along a fault
Modified Mercalli Scale
1) measures intensity of ground shaking(2) measure of the effects of an earthquake on humans, structures for the land itself
Where does the San Andreas Fault (SAF) start and end?
– From Cape Mendocino to Gulf of CA
The SAF is what type of fault?
– Right lateral strike slip fault.
What plates are on either side of the SAF?
– North American Plate and Pacific Plate
How fast are these plates moving past each other (cm/yr)? (SAF)
– 5 cm/yr
What type of plate boundary was CA before the SAF?
– California was a subduction plate boundary from ~ 150 million to 28 to 24 million years, evolved into a transform plate boundary
What is the name of the other major fault (east of the SAF) in the Bay area?
– Hayward Fault
Is the probability for an earthquake along the SAF the same everywhere?
What was emphasized about Parkfield?
a) Earthquake capital of the world, 90 percent chance there will be an earthquake thereb) the most comprehensively instrumented section of a fault anywhere in the world.
Where was the last great earthquake on the SAF?
– Mojave segment when it ruptured- 1857, 8.2
Which of the 3 southern segments mentioned below ruptured during this great earthquake event?
– Mojave Segment, San BErnadino Segment, and Coachella Statement
i) santacruz to Parkfield (between LA and SF) ii) Continuous motioniii) strain releasediv) earthquakes never about 6.0
– Sesimic Gap
What is the concern about LA and the Coachella segment?
b) Energy will propagate north and bounce off the San Gabriel Mountains and straight into downtown LAc) Coachella Evaluation- It’s been longer since there has been an earthquake, and energy will affect LA
left bend in SAF northeast of LA and Santa Barbara regions causes shear stress to turn into compressional stressb) Compressive stress causes:i) Secondary faults:ii) thrust and reverse faultsiii) Mountains
What fault is a threat to Downtown LA?
– Puente Hills fault
Where is the Rose Canyon Fault, Elsinore Fault, San Jacinto Fault, and SAF?
Order of Faults from East to West
Rose Canyon Fault, Elsinore Fault, San Jacinto Fault, and SAF
Where are the Mojave, San BErnadino,and Coachella valley segments along the SAF?
NOT next to fault
New Madrid Fault Zone
Central USfailed anicent riftnot on plate boundary