Download - Catalyst

Volcanic eruptions can be classified according to the Volcanic Explosivity
Index, which is based on several measurable factors that are directly
related to the explosiveness of the eruption, inluding: volume of tephra
ejected, cloud column height, eruption type, duration of continuous blast.
Volcanic Hazards
Primary Effects
-lava flows
-pyroclastic eruptions
-poisonous gas emissions
Secondary Effects
-mudflows and debris avalanches
-flooding (glacial outburst floods)
-tsunamis
-seismicity
-atmospheric effects and climate
change
Volcanic Hazards along the Cascadia
Subduction Zone
Predicting Eruptions
Monitoring the Movement of
Magma
-seismic studies
-magnetic field changes
-electrical resistivity
Hawaiian Type Eruption: Basaltic composition lavas. Described as “gentle” or
“effusive” eruption.
Phreatic Eruption: MSH April 4, 1980
Plinian Eruption: St. Pierre 1903
Basaltic eruptions are very fluid and will flow great distances from the vent or
rift. The photo above is taken from the Kilauea rift zone on the Big Island of
Hawaii.
Aa Flow, Hawaii
Pahoehoe Flow, Hawaii
Few fatalities are typically associated with basaltic lava eruptions, as neighborhoods,
such as the one shown here, can be evacuated. Buildings and other human-made
structures are not so lucky!
Basaltic lava flow reaching a neighborhood near
Kilauea, Hawaii.
Lava flow induced fire, Hawaii.
A pyroclastic flow consists of fluidized mixture of partially molten fragments and superheated expanding gases that flow down the flank of a volcanic edifide. Pyroclastic flows
can exceed velocities of 100 km/hr and they are the most deadliest of volcanic hazards.
Pyroclastic eruptions and flows produce some of most devastating effects
associated with volcanism. Destruction is total to any living organism or structure
within the pathway of a pyroclastic flow.
Mt. St. Helens was predisposed to landsliding on the north face of the volcano
because of weakened rock.
Mt. St. Helens May 18, 1980
Mount St. Helens: Pyroclastic flow May 18, 1980.
Devastation is total in the path of a pyroclastic flow. Note the twisted rebar steel in the
damaged concrete support column from an Andean eruption.
Bishop ash was erupted catastrophically 760,000 years ago in eastern California. The
eruption had a VEI = 7 and ashfall accumulated as far Nebraska. The Bishop ash
provides an important stratigraphic marker for middle Pleistocene-aged deposits.
Pyroclastic flows buried Pompeii, Italy under 4 m of ash in 79AD.
Volcanic gases can have direct impact on humans through suffocation or excessive
heat. Volcanic aerosols may impact climate if erupted into the Stratosphere.
Volcanic gases and particulates ejected into the atmosphere during phreatic
eruptions.
Lake Nyos, Cameroon is situated within an active volcanic region of a failed rift zone. It
is one of three volcanic lakes in the world that is saturated with CO2 gas and is
susceptible to catastrophic degassing when the lake water infrequently overturns.
In 1986 Lake Nyos catastrophically overturned releasing tons of
dense CO2, which killed over 1700 local inhabitants and
thousands of livestock.
CO2 gas has been emitted near the Mammoth Lakes region of California. This area is
part of the Long Valley caldera, where a major VEI=7 eruption occurred 760,000 year
ago, as well as minor VEI-1-3 eruptions forming the Inyo-Mono craters.
Seismic data tilt meters indicate that magma is upwelliing beneath the surface in
the Mammoth Lakes area. This activity led USGS scientists to predict that an
eruption would occur in the near future, but it will likely be small. Still waiting?
Volcanic Hazards
Primary Effects
-lava flows
-pyroclastic eruptions
-poisonous gas emissions
Secondary Effects
-mudflows and debris avalanches
-flooding (glacial outburst floods)
-tsunamis
-seismicity
-atmospheric effects and climate change
Volcanic Hazards along the Cascadia Subduction Zone
Predicting Eruptions
Monitoring the Movement of Magma
-seismic studies
-magnetic field changes
-electrical resistivity
Physical Anomalies and Precursor Phenomena
-ground deformation
-change in heat output
-change in the composition of gases
-local seismic activity
Causal Factors for Lahar
Flows
Lahar flow from
Mt. Pinotubo.
Although basaltic eruptions tend to be effusive, contact with snow and ice can
create catastrophic outburst floods.
Bardarbunga caldera, Iceland produced enormous Jokulhlaups (glacial outburst floods),
but did not pose a major hazard to the Icelandic people, because of its isolated location.
Effects of Volcanism on Climate
Change
Volcanic gases have been
shown to be responsible for
global cooling.
The magnitude and extent of
global cooling depends upon the
force of the eruption, the amount
of particular gases emitted and
location of the eruption.
When volcanic gases and fine
dust reach the stratosphere,
they can produce a wide spread
cooling effect.
Emitted SO2 gas combines with H2O to form H2SO4 aerosols in the
stratosphere. Aerosols, such as H2SO4, reflect incoming sunlight and reduce
the Earth’s surface temperature.
Volcanism and Climate Change
Mean acidity levels in the Greenland ice core strongly correlates with known
volcanic eruptions. Increased volcanic activity index (based on acidity record)
is inversely related to global temperature.
The cooling effect tends to be 1-3° C and last only for a 1-2 years.
Volcanic eruptions that occur near the equator, such as Mt. Pinatubo,
Phillippines, have a greater impact on global cooling because aerosols are
erupted into the atmosphere in both hemispheres. Greatest aerosol
distribution following the Mt. Pinatubo eruption of 1992 is shown in red.
The Cascade volcanoes have variable eruption histories. Mt. St. Helens has the
most frequent eruption history of the Cascade volcanoes during the Holocene.
Volcanic tephras are well-preserved
in lacustrine and bog sediment
throughout the Cascades.
Ubiquitous organic matter provides
excellent opportunities to assign
radiocarbon ages to the eruptions.
The Mt. Mazam O (Crater Lake)
eruption occurred ~6800 years ago.
The thickness of the ash layer and grain size of ash shards provide important data
regarding the volcanic source of the volcanic ash. By coring multiple lakes and/or bogs
in a volcanic region the source of the eruption can be determined using the above
criteria as well as the geochemistry of the tephra.
Excavating a trench behind the Hyak moraine at Snoqualmie Pass (ca. 1990).
Mt. St. Helens Wn
Mt. St. Helens Yn
Mazama O
Three tephra layers are present in the sediment record at Snoqualmie Pass. They
have been independently dated using radiocarbon dating of associated organics.
Probability hazard maps require accurate dating of preserved tephra layers.
1A
1B
Tephra distribution of Cascade volcanoes (Mt. Mazama, Mt. St.
Helens, and Glacier Peak, 1A) compared with Longvalley
(Bishop, CA) and Lava Creek (Yellowstone Park), 1B.
Mt. Rainier’s elevation exceeded
16,000 feet above sea level 5000 years
ago.
Following a large edifice collapse
~5000 years ago the mountain
lost ~1500 feet of its summit.
Mt. Rainier contain 90% of the
Cascade’s glacial ice and
permanent snow.
Mt. Rainier’s glacial ice is a major
potential source
A mass of sliding rocks, snow,
and ice swept down the
northeast side of Mount Rainier
volcano about 5,600 years ago.
The large landslide transformed
itself into a lahar (Osceola) and
flowed down the White River
into the Puget Sound.
Oceola Lahar (~5200 yr BP) near Enumclaw,
WA.
Mt. Rainier volcanic
hazard map (USGS).
Glacier Peak has been a very active Cascade volcano over the past 15,000 years.
Isopachs of Glacier Peak tephra distribution (13,100 yr BP).
Eruption history and isopachs of Glacier Peak tephra distribution (13.1 kyr BP).
Following the eruption and related lahar flow that occurred 13.1 – 12.5 kyr
ago, drainage from Glacier Peak was diverted from the Stillaguamish River
drainage to the Sauk River drainage.
Unconsolidated pyroclastic deposits on the north face of Mt. St. Helens were
also a major source of lahar flows that inundated river drainages flowing from
the volcano.
Reworked pyroclastics incorporated into Mt. St.
Helens lahar deposits.
Lahar deposits can be recognized in the field by their poorly sorted grain-size
distribution, silty matrix and composition of largely volcanic-derived sediment.
Primary Effects
-lava flows
-pyroclastic eruptions
-poisonous gas emissions
Secondary Effects
-mudflows and debris avalanches
-flooding (glacial outburst floods)
-tsunamis
-seismicity
-atmospheric effects and climate change
Volcanic Hazards along the Cascadia Subduction
Zone
Predicting Eruptions
Monitoring the Movement of Magma
-seismic studies
-magnetic field changes
-electrical resistivity
Physical Anomalies and Precursor
Phenomena
-ground deformation
-change in heat output
-change in the composition of gases
Can we predict volcanic eruptions?
Yes, but with caveats!!!
1.Requires a thorough understanding of the volcano’s
eruptive history.
2.Requires appropriate instrumentation on the volcano
well in advance of the eruption.
3.Requires constant monitoring of instrumentation so that
incoming data can be properly interpreted.
The science behind predicting volcanoes has improved
substantially over the past decades, but volcanologists
can only provide probabilities regarding the timing of a
given eruption. It is not possible to determine the exact
severity of an eruption or whether the magma will even
reach the surface.
How do volcanoloists
predict volcanic eruptions?
1.Monitor seismic data
related to movement of
magma.
2.Monitor ground
deformation and dome
expansion.
1.Monitor volcanic gases
emitted as magma rises
and expanding gases are
released.
Successful Volcanic Predictions:
Volcanologists predicted the eminence 1980
Mt. St. Helens eruption. Their warnings of an
impending blow prompted the U.S. Forest
Service to evacuate people from dangerous
areas near the volcano. Although 57 people
died in the eruption, it is estimated that as many
as 20,000 lives were saved.
In the spring of 1991, a USGS “SWAT team”
was rushed to the Philippines' Mt. Pinatubo and
successfully predicted the June eruption,
leading to evacuations that saved thousands if
not tens of thousands of lives and millions of
dollars worth of military equipment at the
nearby Clark Air Force Base.