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VOLCANIC HAZARDS
ASSESSMENT
Human-based Data Sources
Geochemical Data
Geophysical Data
ACTIVE vs. EXTINCT
VOLCANOES
• Historians say:
• Active volcanoes are those that are erupting
or showing some activity now.
• Volcanoes that have erupted historically, but
are inactive at present, are Dormant.
• Volcanoes that have had no activity in
historical or archaeological time are Extinct.
ACTIVE vs. EXTINCT
VOLCANOES
• To geologists:
• Active volcanoes have magma
chambers
• Extinct volcanoes have no magma left
in chambers
HUMAN-BASED DATA
• Historical Records
• Archaeology
• Oral Tradition
• These can help extend the record back to a
few thousand years
GEOCHEMICAL DATA
• Radiometric Dates on Volcanic Materials–
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Can extend dates back to millions of years
Give date of last eruption
Give repeat interval of past events
Show which types of volcanic products are
expected
Geophysical Data are used to
assess Present-day Risk
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Is Magma Present? Determined by S-wave activity
Heat Flow, especially if increasing
Earthquake Patterns -shallow concentric patterns
Tilting or Bulge of Surface from GPS Data,
Surveying, SAR Interferometry
Earthquakes in Hawaii
Earthquakes
In Iceland
Interferometry:
Layering two Images
of separate times
on top of one another
to measure vertical change
Top: visual spectrum shows nothing new
Bottom: Interferogram measures areas
of differential change due to ground
swelling upward. Maximum displacement
is in center and pattern is concentric,
suggesting a pending volcanic eruption
VOLCANOES IN THE US
There are 33 active volcanoes in the US
Most are at convergent plate boundaries in Alaska and N. California,
Oregon, and Washington. These are all stratovolcanoes, which are the
most dangerous in terms of explosive activity.
Some are on or near hotspots: Hawaii’s volcanoes, and Yellowstone
Some are former CPB: Central and Southern California
The remainder are on a failed rift (former divergent plate boundary):
Arizona, New Mexico
VOLCANIC HAZARDS
• Lava flows
• Pyroclastics
• Gases
– Heated air
– Toxic components
– Climate change
• Lahars
• Tsunamis
• Earthquakes
Volcanic Gases:
80% H2O, plus CO2, SO2, and also CO,
H2S
GLOBAL COOLING DUE TO LARGE ERUPTION
Ash injected into
Stratosphere circulates
around the world
for up to 3 years
Lahar floods Armero, Colombia
after eruption of Nevado del Ruiz
Krakatau, 1883
Lava and slope collapse produced a tsunami
up to 40m high.
-Killed 36,000 people in SE Asia
-Effects of Tsunami felt 7000 miles away
Ash and gases produced global cooling
that lasted 3 years