Part 4: Volcanic Hazards & MonitoringPart 4: Volcanic Hazards & Monitoring
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Slide show prepared by Slide show prepared by Dr. Beth Pratt-Sitaula (Central Washington University) and Jenda Johnson (IRIS).Dr. Beth Pratt-Sitaula (Central Washington University) and Jenda Johnson (IRIS).
Volcanoes are…
An opening on the planet’s surface where molten rock, ash, or gases escape from below
Aleutian Islands, AK; International Space Station photo
http://earthquake.usgs.gov/monitoring/anss/regions/hi/
1. Volcanoes are steep-sided and ooze hot runny lava
FALSE FALSE - - ““Hot runnyHot runny”” volcanoes are volcanoes are mostly flat or shield likemostly flat or shield like
Volcano Prior Knowledge SurveyVolcano Prior Knowledge Survey
TRUE/FALSE –> thumbs up OR downTRUE/FALSE –> thumbs up OR down
http://www.imdb.com/media/rm1327600128/tt0445548
Volcano Prior Knowledge SurveyVolcano Prior Knowledge Survey
2. The biggest eruptions flatten topography.
TRUE TRUE – – largest volumelargest volume eruptions eruptions lead to flood basalt plateaus; lead to flood basalt plateaus; most explosivemost explosive eruptions lead to eruptions lead to mountains getting blown to bitsmountains getting blown to bits
TRUE/FALSE –> thumbs up OR downTRUE/FALSE –> thumbs up OR down
http://www.imdb.com/media/rm1327600128/tt0445548
Volcano Prior Knowledge SurveyVolcano Prior Knowledge Survey
3. Magma chambers are…big chambers of liquid rock
FALSE - Magma FALSE - Magma ““chamberschambers”” form form when lava is injected in cracks and when lava is injected in cracks and crevasses and pushes against crevasses and pushes against existing rock. They are usually existing rock. They are usually more of a plumbing system than a more of a plumbing system than a chamber.chamber.
TRUE/FALSE –> thumbs up OR downTRUE/FALSE –> thumbs up OR down
SHOW ANIMATION “Mesozoic Subduction” from URL below.http://emvc.geol.ucsb.edu/2_infopgs/IP1GTect/cSubduction.html
• How many active volcanoes on Earth?
• How many volcanoes erupt per year?
• How many people are killed by volcanoes?
~1,500 active volcanoes~1,500 active volcanoes
~60 volcanoes erupt per year~60 volcanoes erupt per year
~200,000 in the last 200 years~200,000 in the last 200 years
Some volcano statsSome volcano stats
Where does molten rock come from?
Modified from USGS Graphics
Where do volcanoes form?
• Subduction zones
• “Hot spots”
• Mid-ocean ridges
• Continental rift zones
Rocks melt under certain circumstances
1. Heating
2. Decompression
3. Reducing melting temp by adding water
Types of Volcanoes
Flood Basalts
Millions km3 of horizontal
basalt layers
Columbia Flood Basalts Photo by Thor Thordarsson
Why do different magmas behave differently & make very different volcanoes?
• VISCOSITY
• VOLATILES
• VOLUME
“3 Vs” •WATER
•CARBON DIOXIDE
•Sulfur dioxide
•Hydrogen sulfide
Viscosity determines:
1. The flow rate of magma
2. VOLATILE trapping
vs
Viscosity depends on chemical composition
http://volcanoes.usgs.gov/images/pglossary/VolRocks.php
Types of Volcanoes
Flood Basalts
Millions km3 of horizontal
basalt layers
Columbia Flood Basalts Photo by Thor Thordarsson
Flood basalts
• Extremely low viscosity
• Few volatiles (non-explosive)
• Very very large volume
http://www.fas.org/irp/imint/docs/rst/Sect17/Sect17_3.html
Flood basalts - HAZARDS
• Bury your state in lava
• Huge green house gas release
• Geologic ennui (if you find basalt dull)
http://www.fas.org/irp/imint/docs/rst/Sect17/Sect17_3.html
Columbia River Flood Basalts
• Over 300 separate flows averaging 580 km3 EACH• 3.5 km thick in places• Erupted 17.5-6 Ma• ~90% erupted 16-15 Ma http://geosphere.gsapubs.org/content/4/3/480.full.pdf+html
Thor Thordarsson
Shield Volcanoes
• Low viscosity
• Few volatiles (non-explosive)
• Large volume
Mauna Loa, Hawaii USGS
Shield Volcanoes - HAZARDS
• Lava flows
• Volcanic gasses (esp. CO2)
Medicine Lake Volcano, CA USGS
Cinder cone (or scoria cone)
• Moderate viscosity
• Some volatiles
• Small volume
Image released to public domain by Q Myers (English Wikipedia)
~600 m
Lava Butte, OR
Stratovolcano
• Mod–high viscosity
• Few-many volatiles (mod-very explosive)
• Mod-large volume
Mt Rainier and Seattle, WA
&
Stratovolcano – multiple types of eruption processes
Lava dome
Ash cloud
Pyroclastic flows
USGS Mt. St. Helens, 1984
USGS Mt Mayon, Philippines, 2006
http://www.tulane.edu/~sanelson/geol111/igneous.htm
Stratovolcano - Mt St Helens
Before 1980 eruptionbuilt up
USGS
USGS
After 1980 eruptionblown to bits
Stratovolcano - HAZARDS• Pretty much all types of volcanic hazards
USGS
Stratovolcanoes – PACIFIC NW
Most Cascade volcanoes are stratovolcanoes (typical for subduction zones)
Stratovolcano
shield vs composite
Mauna Loa’s full height = 19,000 ft + 13,000 ft = 32,000 ft
below sea level
above sea level
Mt Rainer = 14,400 ft
Caldera formation
Magma chamber partially emptied during eruption
Center collapses down and forces out more magma
Caldera is formed
Coke w/dry ice
• High viscosity• Many volatiles (very explosive)• Large volume
http://pubs.usgs.gov/fs/2002/fs092-02/
Caldera formation - HAZARDS• Ash falls• Pyroclastic flows• Volcanic landslides• Volcanic gasses
http://pubs.usgs.gov/fs/2002/fs092-02/
Crater Lake Caldera, OR
Continental Hotspot CalderaYellowstone, WY
http://pubs.usgs.gov/fs/fs100-03/
Yellowstone Eruptions
http://www.nps.gov/yell/naturescience/eruptions.htm
http://pubs.usgs.gov/fs/2005/3024/
Snake River Plain, IdahoPossible Hot Spot Trail from SW to NE over last 16 Ma
16 Ma
10 Ma
5 Ma 2 Ma1.3 Ma
0.6 Ma
ID
UT
WY
NV
OR
Image after Smith & Siegel (2000), Windows into the Earth: the Geological Story of Yellowstone and Grand Teton National Parks
80 km
Proposed relationship between flood basalts & hotspots
Columbia Flood Basalts
Yellowstone hotspot track~16 Ma
Cascade Volcanoes
Show real roll-over
Below Cascade volcanoes
Major rock types
CLASSIFICATION OF INTRUSIVE ROCKS
Gabbro Diorite Granodiorite Granite
Volcanic Hazards
• Pyroclastic flow (a.k.a. ash flow)
• Lahar (a.k.a. mud flow or debris flow)
• Gases
• Ash falls
• Volcanic Landslides
• Lava Flows
• Tsunamis USGS
Show Understanding Volcanic Hazards clips
Mt Rainier Lahar Hazard
Ash fall hazard
USGS
The Science of PredictionMonitoring Volcanic Activity
Signs of Volcanic Activity
Scientists look for five signs that volcanic processes are at work
• Eruption History
• Volcanic Gases
• Heat and Hydrothermal Activity
• Earthquakes
• Ground deformation
Monitoring
Scientists use many tools to monitor volcanoes
Since erupting volcanoes are dangerous, they prefer tools that can be set up and left
Image from USGS (2002) Volcano Hazards Program: Strategy for reducing volcanic risk http://volcanoes.usgs.gov/
Volcanic Gases
Volcanic gases are hazardous and hard to sample – they can be detected using :
• Spectrometers mounted on ground or airplane
• Samples collected by hand and analyzing in a laboratory
Image from USGS Volcano Hazards Program “Measuring volcanic gases: emission rates of sulfur dioxide and carbon dioxide in volcanic plumes.” http://volcanoes.usgs.gov/About/What/Monitor/Gas/plumes.html
A scientist collects gas samples (Note the protective equipment)
Volcanic Gases
• Trees and animals can be effected by gasses and aid detection
• Trees at Mammoth Mt, CA died when CO2 suffocated their roots
Image from USGS Fact Sheet 172-96 “Invisible CO2 Gas Killing Trees at Mammoth Mountain, California” http://pubs.usgs.gov/fs/fs172-96/
Heat & Hydrothermal Activity
Hydrothermal activity demonstrates presence of magma, not necessarily magma movement
Thermal features can be monitored by:• Night aerial observations
• Thermal (infrared) imaging
• Direct temperature measurements
Image from (2007) USGS Mount St. Helens, Washington Forward Looking Infrared Images http://vulcan.wr.usgs.gov/Imgs/Jpg/MSH/MSH07/MSH07_area_new_growth_on_dome_06-26-07_FLIR_med.jpg
Infrared image of Mt. St. Helens’ new lava
dome June 26th 2007
Earthquakes
• Moving magma and volcanic fluids cause quakes
• Most volcanic earthquakes are:• <3 Magnitude• Shallower than 10 km• Occur in swarms
Magma risesMagma and gases exert pressure
Rocks break, triggering earthquakes
Image from USGS Volcano Hazards Program “Monitoring Volcano Seismicity.” http://volcanoes.usgs.gov/activity/methods/seismic/index.php
Earthquakes
Scientists can tell where Mt. St. Helens’ magma source is by looking at earthquake pattern.
Ground Deformation
• Volcanoes change shape before, during, and after eruptions
• Deformation is caused by trapped and pressurized gases or fluids (monitor gas emissions too!)
• Usually accompanied by swarms of shallow earthquakes (monitor seismicity too!)
Image from USGS Volcano Hazards Program “Monitoring Volcano Seismicity.” http://volcanoes.usgs.gov/activity/methods/seismic/index.php
Ground Deformation
Deformation is measured using:
•Tiltmeters (big, underground carpenter’s level)
•Global Positioning System (satellites triangulate position)
•Leveling Survey (periodic repeat measurements)
GPS site Augustine Volcano, Alaska
Mt St Helens image from USGS Volcano Hazards Program “Monitoring Volcano Ground Deformation.” http://volcanoes.usgs.gov/activity/methods/deformation/tilt/msh.php
Tiltmeter at Mt St Helens’ crater floor
Science of Prediction
Even though scientists could not predict the exact moment when Mt. St. Helens would erupt, they were able to save many lives by predicting that it would erupt.
Table 1. SUMMARY OF VOLCANIC-ALERT LEVELS
NORMAL Typical background activity of a volcano in a non-eruptive state After a change from a higher level: Volcanic activity considered to have ceased, and volcano reverted to its normal, non- eruptive state.
ADVISORY Elevated unrest above known background
activity After a change from a higher level: Volcanic activity has decreased significantly but continues to be closely monitored for possible renewed increase.
WATCH Heightened/escalating unrest with increased potential for eruptive activity (timeframe variable) OR a minor eruption underway that poses limited hazards
WARNING Highly hazardous eruption underway or imminent
Table from USGS Volcano Hazards Program “USGS Volcanic Activity Alert – Notification System” http://volcanoes.usgs.gov/activity/alertsystem/
Volcanic monitoring animations by
http://www.iris.edu/hq/programs/education_and_outreach/animations#CC
Mt St Helens erupted a lava dome 2004-2008
What direction did the GPS stations move during this eruption?
– Outwards?
– Inwards?
http://vulcan.wr.usgs.gov/Volcanoes/MSH/Eruption04/Monitoring/February2008/
Mt St Helens GPS data 2004-5
Lisowski et al, UNAVCO proposal, 2008