Lava flow
Lahar
Volcanic Hazards
Ash fall
Pyroclastic flow
Landslides
Volcanic Hazards
Mt. St. Helens: before the 1980
eruption
Bulge: plug
that is pushed
out by magma
within the
conduit.
Pyroclastic eruption
•Mt. St. Helens
•Landslide
•Release of pressure
•Lateral blast
•Pyroclastic flowdown with the pull
of gravity
•Ash cloud-vertical
•Ash fall
Landslide
• Gravitational force “pulls” unstable
material down slope
• Fills canyons and valleys with debris
Landslide, Mt. Shasta
• 300,000 years ago
• 20 times more
material than the Mt.
St. Helens landslide
Lateral Blast: extreme
pyroclastic flow
• In the case of Mt. St. Helens, the landslide
“uncorked” the vent.
• Gas and debris were released under
tremendous force
• Burns and destroys anything in its path
Lateral Blast
• Large area
completely
devastated (23 X19
miles)
• Trees knocked down
• Vegetation burned off
Mt. Unzen,
Japan
Geologists examined
volcanoes all around the
world.
Mt. Unzen, Japan and Mt.
Hood, Washington have the
potential for lateral
eruptions.
Pyroclastic flow: hot gas propels
pyroclastic debris
Gravitational force pulls
hot gas and pyroclastic
debris down slope from
the initial vertical
eruption.
Montserrat, 1997
Pyroclastic Flow
• Mt. Pinatubo,
Philippines
• 1991
• May reach 100 miles
per hour
• Burns or suffocates
anything in its path
Vertical Eruptions: Plinian
• If the initial eruption is vertical the force
sends debris into the stratosphere
Global cooling: debris blocks
sunlight
Mt.
Pinatubo
Major eruptions
blocking Sun’s
radiation
Cooled global temperatures by .5-.6
degrees Centigrade
Volcanism
• 1815- Large eruption in the tropics; once
thought to be Tambora in Indonesia
– Global temperatures fell
– Crops failed throughout Europe and famine
spread
– Mary Shelly told her house guests the story of
Frankenstein and his creator died in the arctic
because they were unable to go outside
during their vacation
Ash fall
• Acts as an abrasive
• Clogs machinery,
covers vegetation,
irritates lungs and
eyes
Photomicrograph of ash from the Mt.
Tehama eruption (Lassen Peak)
Ash deposited associated with the
eruption of the Long Valley Caldera
Iceland
• Located on the
North Atlantic midoceanic ridge
• Hot spot
• What type of lava?
• Viscosity?
• Eruptive style?
Iceland's Eyjafjallajokull volcano
• Volcanic eruption
under ice produces
steam and other
gases to propel
pyroclastic debris
into the
atmosphere
• European air travel
was interrupted for
weeks
Mt. Yasur, May 30, 2010
• Some flights
rerouted or
cancelled in
Australia
Volume of Pyroclastic Debris
Ash
Lahars
• Remobilized ash, rock and debris by water
• Water source needed: rain, snow melt
Mt. St. Helens
Mt. Rainier: lahars from the last
5600 years
Lahars: Mt. Pinatubo
Lava Flow
• Destroys everything in path
• People and animals can usually escape
Iceland: The Eldfell volcano on
the island of Heimaey
• New land was created during the 1973
eruption.
Jokulhlaup
• One third of country is
covered by active
volcanoes
• About 13% covered
by glaciers
• The lava melts the ice
cap
• At one point the large
volume of water pours
rapidly to the
adjacent area
Gas Emissions
• Sometimes gas release is concentrated
and toxic to vegetation and people
Horseshoe Lake near Mammoth, California
Carbon dioxide leaked out of
Lake Nyos, Africa suffocating
1700 people and all animal life.
Understanding Volcanic Hazards
• Past history
– How often
– Types of hazards
– Extent of hazards
– Location of past events
Ash deposits
associated with the
eruption of Santorini,
Greece