Natural Disasters- Exam 2 (Baker-Treloar)

Mt. Rainier
– Subduction in ROF- Cascades- potentially most dangerous in Cascades- lahar will seriously damage
Mt. St. Helens, 1980
– Subduction in ROF- Cascades- Large Landslides,lateral blasts,lahar and pyroclastic flows- Most active in Cascades
What are volcanic rocks classified as?
Igneous Rocks
What are three types of volcanic rocks?
Andesite, Rhyolite, Basalt
What type of tectonic setting do you find Andesite and Rhyolite Rocks?
Subduction Zones
What type of tectonic setting do you find Basalt Rocks?
Mid Ocean Ridges and Hot Spots
-Dark color-Low viscosity (flows easily)-Quiet eruption-Composition of ocean’s crust-Erupts Divergent plate boundaries (MORs) and Hot spots
What are the two most common elements in the crust?
Silicon and Oxygen
Which 2 elements are always found in minerals that make up volcanic rocks?
Silicon and Oxygen*They control the viscosity
Shield Volcanoes
– large volcanoes with broad, gentle slopes built by basalt flows- Hot spot volcanoes
Iceland, 1783
-Greatest lava eruption of historic times-large basalt flow-divergent plate boundary-Laki fissure erupts for 8 months
Iceland, 1973
-Most recent large basalt flow-Nearly closed harbor at Heimaey-divergent plate boundary
-Most active volcano in the world-Hot spot-In the Ring of Fire
What are the 2 types of Basalt flows?
Pahoehoe and aa
Pahoehoe flow
Lava cools to form smooth,ropy texture
aa flow
Lava cools to form rough, blocky texture(sharp, no flip-flops)
Lava Tube
-Tunnels beneath the surface of cooled basalt-Inactive tubes
What are the major gasses emitted from volcanoes?
-Water Vapor (50 %)-Carbon Dioxide (CO2)-Sulfur Dioxide (SO2)
Which gas is responsible for global cooling?
Sulfur Dioxide(Blocks some of the Sun before it heats up the Earth)
Which gas is responsible for global cooling?
Carbon Dioxide
Andesite and Rhyolite
-Gray-green-brown color-High viscosity (doesn’t flow easily) -Explosive-most common in Subduction zones (convergent plate boundaries) and Ring of Fire volcanoes
Pyroclastics or “tephra”
-“Fire Fragments”- More common with viscous magma (AKA andesite/rhyolite)- Ejects fragments of ash, pumice, bombs, and blocks
Eruption Column
-the mass of ash and gases forcefully blown up from a volcanic vent during an eruption-cylindrical-typical style of subduction zone voclanoes
Plinian Eruption
-tall and large eruption column (approximately 30 miles)- Examples: Vesuvius and Mt.

St Helens, 1980

Composite Volcano or “stratovolcano”
-Volcano made up of alternating layers of pyroclastics and lavaflows- Most common in Subduction Zones and Ring of Fire-Explosive eruptions- Ex: West Pacific, Alaska
– A large depression in the summit of a volcano- formed by collapse into underlying magma chamber- usually more than 1 km across- Ex: Mt. Pinatubo Caldera, Phillipines 1991
– depression on the summit of a volcano- less than 1 km
Lava Dome
– Viscous lava solidifies in caldera or crater of a composite volcano- Acts as a “plug”-Ex: Mt. St Helens, 1980
What is the difference between a shield volcano and a composite volcano?
Sheild Volcanoes: Fluid Basalt flowssComposite Volcanoes: pyroclastics and lava flows (andesite, rhyolite)
Pyroclastic Flows
– 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
Lahar Events
– 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
El Popo
– 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!)
Krakatau, 1883
– Subduction in ROF- Indian Ocean/ Indonesia- generated 120 ft tsunami
Tombora, 1815
– 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
Soufriere Hills
– 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
Mt. Vesuvius, 79 AD
– Subduction OUTSIDE of ROF- Italy, Mediterranean- Pyroclastics flow – Ash fall- Buried Pompeii
Long Valley Caldera
– No subduction or Hot Spot – Calif, Sierra Nevada- Soon-to-be huge eruption
Yellowstone Caldera
– Hot Spot- US- Most debris from an eruption ever- Obliterated mountain range- Magma chamber is building
Origin of earthquake or area of fault rupture, most are shallow, weak region in the fault
What are some precursors to volcanic eruptions?
– Earthquake activity that steadily increase- Volcano will swell- Gas will be emitted
Surface directly above focus, not always on fault
Force applied (compressional, tensional, shear)
Force applied (compressional, tensional, shear)
Change due to stress (deformation in rocks)
Elastic Rebound Theory
Explains how rocks respond to stress, why earthquakes occur
Means of locating the epicenter, P and S wave time delay, needs to be 3 sources of data
The study of historic earthquakes
Seismic Tomography
3-D image of earth’s interior using P wave velocities because they go through liquids and solids
Seismic Gap
Lack in seismic activity in an area along a fault or a subduction zone
Amplifying effect produced when the natural vibration frequency of ground or structure is matched by the frequency of seismic waves
Wet sand or oil can become liquid-like when strongly shaken
Fault creep
Ground displacement, Offset, Slip
– Fences and cracks that are moved during an earthquake- Ground moves from earthquakes
Chile, 1960
– Tsunami event- 9.5 subduction zone earthquake- Largest earthquake recorded- Tsunami traveled to Hawaii and Japan
Alaska, 1964
– Tsunami event- 9.2 subduction earthquake- Largest US earthquake- Tsunami wave traveled to Northern CA – Extensive ground rupture- landslidesvi) liquefaction
Cascadia Subduction Zone
– Tsunami event- Has the potential to generate a magnitude 8 to 9 earthquake- Happened 300 years ago- Subduction event with major tsunami
Indian Ocean, 2004 (Sumatra, Indonesia)
– Tsunami event- 9.2 subduction mega thrust earthquake- Tsunami generated- Seismic gapIndonesi
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
Haiti, 2010
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
Northridge, 1994
– 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
China, 1975
(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
Alaska, 1964
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
Chili, 1960
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
Indonesia, 2004
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
Pakistan, 2005
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
P waves
– Primary Waves- compressional waves- Felt first, fastest, in a push-pull manner (like a slinky)
S Waves
– 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
Richter Magnitude
– 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?
– No
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
Creeping Section
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
“Big Bend”
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?
Southern CA
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?
Southern CA
Mojave desert
NOT next to fault
New Madrid Fault Zone
Central USfailed anicent riftnot on plate boundary