Part 4: Volcanic Hazards & Part 4: Volcanic Hazards & Monitoring Monitoring • “Normal ” view has a Notes panel below with lecture notes and links to video lectures, activities, or web sites. •“Slide Show ” view has animated elements that pop up on clicking •Video & animations were removed to increase speed. Download information is in the Notes panel in Normal view. If you got this slide show on a DVD, the related animations will also be in a folder associated with the PowerPoint. • Modify slide show liberally for your own needs! Slide show prepared by Slide show prepared by Dr. Beth Pratt-Sitaula (Central Washington University) and Jenda Dr. Beth Pratt-Sitaula (Central Washington University) and Jenda Johnson (IRIS). Johnson (IRIS).
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Part 4: Volcanic Hazards & Monitoring “Normal” view has a Notes panel below with lecture notes and links to video lectures, activities, or web sites. “Slide.
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• “Normal” view has a Notes panel below with lecture notes and links to video lectures, activities, or web sites.
•“Slide Show” view has animated elements that pop up on clicking
•Video & animations were removed to increase speed. Download information is in the Notes panel in Normal view. If you got this slide show on a DVD, the related animations will also be in a folder associated with the PowerPoint.
• Modify slide show liberally for your own needs!
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
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
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?
• 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
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
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/