Part 4: Volcanic Hazards & Monitoring
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Slide show prepared by
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/
Volcano Prior Knowledge Survey
TRUE/FALSE –> thumbs up OR down
1. Volcanoes are steep-sided and ooze hot
runny lava
FALSE - “Hot runny” volcanoes are
mostly flat or shield like
http://www.imdb.com/m
edia/rm1327600128/tt
0445548
Volcano Prior Knowledge Survey
TRUE/FALSE –> thumbs up OR down
2. The biggest eruptions flatten
topography.
TRUE – largest volume eruptions lead
to flood basalt plateaus;
most explosive eruptions lead to
mountains getting blown to bits
http://www.imdb.com/m
edia/rm1327600128/tt
0445548
Volcano Prior Knowledge Survey
TRUE/FALSE –> thumbs up OR down
3. Magma chambers are…big chambers of
liquid rock
FALSE - Magma “chambers” form
when lava is injected in cracks and
crevasses and pushes against existing
rock. They are usually more of a
plumbing system than a chamber.
SHOW ANIMATION “Mesozoic Subduction” from URL below.
http://emvc.geol.ucsb.edu/2_infopgs/IP1GTect/cSubduction.html
Some volcano stats
• How many active volcanoes on Earth?
~1,500 active volcanoes
• How many volcanoes erupt per year?
~60 volcanoes erupt per year
• How many people are killed by volcanoes?
~200,000 in the last 200 years
Where does molten rock come from?
Modified from USGS Graphics
Where do volcanoes form?
• Subduction zones
• Mid-ocean ridges
• “Hot spots”
• 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
“3 Vs”• VOLATILES
• VOLUME
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
http://www.fas.org/irp/imint/docs/rst/Sect17/Sect17_3.html
• Extremely low viscosity
• Few volatiles (non-explosive)
• Very very large volume
Flood basalts - HAZARDS
http://www.fas.org/irp/imint/docs/rst/Sect17/Sect17_3.html
• Bury your state in lava
• Huge green house gas release
• Geologic ennui (if you find basalt dull)
Columbia River Flood Basalts
Thor Thordarsson
• 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
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
Lava Butte, OR
~600 m
Image released to public domain by Q Myers (English Wikipedia)
Stratovolcano
• Mod–high viscosity
• Few-many volatiles (mod-very explosive)
• Mod-large volume
&
Mt Rainier and Seattle, WA
Ash cloud
Stratovolcano
– multiple types of
eruption processes
Pyroclastic flows
USGS
Mt Mayon, Philippines, 2006
Lava dome
USGS
Mt. St. Helens, 1984
http://www.tulane.edu/~sanelson/g
eol111/igneous.htm
Stratovolcano - Mt St Helens
USGS
Before 1980 eruption
built up
USGS
After 1980 eruption
blown 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
Mt Rainer = 14,400 ft
Caldera formation
• High viscosity
• Many volatiles (very explosive)
• Large volume
Coke w/
dry ice
Magma chamber
partially emptied
during eruption
Center collapses
down and forces
out more magma
Caldera is formed
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 Caldera
Yellowstone, WY
http://pubs.usgs.gov/fs/fs100-03/
Yellowstone Eruptions
http://pubs.usgs.gov/fs/2005/3024/
http://www.nps.gov/yell/natu
rescience/eruptions.htm
Snake River Plain, Idaho
Possible Hot Spot Trail from SW to NE over
last 16 Ma
OR
1.3 Ma
0.6 Ma
2 Ma
5 Ma
10 Ma
16 Ma
ID
NV
UT
WY
80 km
Image after Smith & Siegel (2000), Windows into the Earth: the Geological
Story of Yellowstone and Grand Teton National Parks
Columbia
Flood
Basalts
~16 Ma
Yellowstone
hotspot track
Proposed
relationship
between
flood basalts
& hotspots
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 Prediction
Monitoring 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
A scientist collects gas samples
(Note the protective equipment)
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
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
Infrared image of Mt. St. Helens’ new lava
dome June 26th 2007
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_06-2607_FLIR_med.jpg
Earthquakes
• Moving magma and volcanic fluids cause quakes
• Most volcanic earthquakes are:
• <3 Magnitude
• Shallower than 10 km
• Occur in swarms
Magma rises
Magma and
gases exert
pressure
Rocks break,
triggering
earthquakes
Image from USGS Volcano
Hazards Program
“Monitoring Volcano
Seismicity.”
http://volcanoes.usgs.gov/
activity/methods/seismic/in
dex.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/activ
ity/methods/seismic/index.php
Ground Deformation
Deformation is measured
using:
Tiltmeter at Mt St
Helens’ crater floor
•Tiltmeters (big, underground
carpenter’s level)
•Global Positioning System
(satellites triangulate
position)
Mt St Helens image
from USGS Volcano
Hazards Program
“Monitoring Volcano
Ground
Deformation.”
http://volcanoes.usgs
.gov/activity/methods
/deformation/tilt/msh
.php
•Leveling Survey (periodic
repeat measurements)
GPS site Augustine
Volcano, Alaska
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 VOLCANICALERT LEVELS
NORMAL
Typical background activity
of a volcano in a noneruptive state After a
change from a higher level:
Volcanic activity considered
to have ceased, and volcano
reverted to its normal, noneruptive 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_outreac
h/animations#CC
Mt St Helens erupted a lava
dome 2004-2008
http://vulcan.wr.usgs.gov/Volcanoes/MSH/Eruption04/Monitoring/February2008/
What direction did the GPS stations move
during this eruption?
– Outwards?
– Inwards?
Mt St Helens GPS data 2004-5
Lisowski et al, UNAVCO proposal, 2008