Download Shield Volcanos

PH307 Disasters: Volcanos
Dr. Dirk Froebrich
This presentation can be found at:
http://astro.kent.ac.uk/~df/teaching/ph307/disasters_volcanos.ppt
Volcanos
Kílauea, Hawai‘i
Mauna Kea, Hawai‘i
... The summit appears utterly lifeless except
for a few unlucky bugs blown up from below
and a few flightless native insects that feed
on them. No trees, no plants. Just lifeless
void. The mountain last erupted 4500years
ago and is considered dormant. (If it erupts
when you are up there, please disregard this
last statement.)
4205m
Outline
causes of volcanism
types of volcanos
types of eruptions
methods of predicting eruptions
dangers, effects
and how to minimise damage/loss of life
 Seminar
Causes of Volcanism
Active Volcanos (~1900)
Earthquake Epicenters since 1963
Plate Tectonics
Plate Tectonics
Types of Volcanos
Volcano Types (by position)
mid ocean ridges
usually at sea floor, but e.g. Iceland
subduction zones
e.g. Mt. Etna, the Ring of Fire
Hotspots/Plumes
e.g. Hawai‘i, Eifel, Auvergne
Volcanos in Subduction zones
Mount Etna
Hotspot Volcanos
Hotspot Volcanos
Volcano Types (by shape)
Shield Volcanos
- huge quantities of basaltic lava gradually build up wide shield like mountain
- hot fluid lava flows
- e.g. Hawai‘i
Shield Volcanos
Skjaldbreidur
Olympus Mons (Mars)
Mt. Edziza
Mauna Loa
Volcano Types (by shape)
Shield Volcanos
- huge quantities of basaltic lava gradually build up wide shield like mountain
- hot fluid lava flows
- e.g. Hawai‘i
Strato Volcanos
- strata – internally consistent layer of rock
- tall conical mountain build up by a sequence of lava flows and ejecta
- e.g. Mt. Fuji, Vesuvius, Stromboli, Popocatépetl, Mt. St. Helens
Strato Volcanos
Mt. Fuji
Stromboli
Mt. St. Helens
Popocatépetl
Volcano Types (by shape)
Shield Volcanos
- huge quantities of basaltic lava gradually build up wide shield like mountain
- hot fluid lava flows
- e.g. Hawai‘i
Strato Volcanos
- strata – internally consistent layer of rock
- tall conical mountain build up by a sequence of lava flows and ejecta
- e.g. Mt. Fuji, Vesuvius, Stromboli, Popocatépetl, Mt. St. Helens
Cinder Cones
- small (30-400m high), build up around vents
- can be on flanks of other volcanos or isolated
Submarine & Subglacial Volcanos
Supervolcanos
- large calderas
- eruptions on enourmous scales
Supervolcanos
Mt. Aso
Campi Flegrei
Lake Taupo
Yellowstone Caldera
Type of Eruptions
Eruption Types
Subglacial
Strombolian
Vulcanian
Peléan
Hawai‘ian
Phreatic
Plinian
Subglacial Eruption
- under ice or glacier
- risk of floods, lahars
- rare type (only 5 active)
- e.g. Iceland
Subglacial eruption: 1 water vapor
cloud, 2 lake, 3 ice, 4 pillow lava, 5
magma conduit, 6 magma chamber
Strombolian Eruption
- named after Mt. Stromboli
- low level eruptions
- ejection of cinder and lava bombs
between 10 and a few 100m
- viscous lava flows
- gas bubbles (slugs) rise through
magma and burst near the top
- slugs form deep (~3km) and are
hence difficult to predict
- long lasting eruptions (up to
decades)
Vulcanian Eruption
- named after Vulcano Island
- rising magma makes contact with
ground or surface water
- extreme temperatures result in near
instantaneous evaporation to steam
 explosion
- dangers from exploding steam,
water, ash, rock, volcanic bombs
Vulcanian eruption: 1 Ash plume, 2
Lapilli, 3 Volcanic ash rain, 4 Lava
fountain, 5 Volcanic bomb, 6 Lava
flow, 7 Sill, 8 Magma conduit, 9
Magma chamber, 0 Dike
Peléan Eruption
Mt. Mayon
- named after Mt. Pelée
- glowing cloud eruption
- huge amounts of gas, dust, ash, lava
fragments are blown out of a crater
- fall back  avalanche down with
100mph (pyroclastic flows)
Pelean eruption: 1 Ash plume, 2 Volcanic
ash rain, 3 Lava dome, 4 Volcanic bomb,
5 Pyroclastic flow, 6 Magma conduit, 7
Magma chamber, 8 Dike
Hawai‘ian Eruption
- named after eruptions in Hawai‘i
- occur along fissures, (central) vents
- gentle, low level eruptions, lava
fountains up to 600m high,
- low viscosity lava
- safest eruptions for tourism 
Hawaiian eruption: 1 Ash plume, 2
Lava fountain, 3 Crater, 4 Lava lake, 5
Fumaroles, 6 Lava flow, 7 Sill, 8
Magma conduit, 9 Magma chamber,
0 Dike
Phreatic Eruption
- steam blast eruption
- explosive expanding steam from ground
or surface water
- only pre-existing solid rock, no new
magma is ejected
- danger from steam, rock fragments,
poisonous gases, asphyxiation
- e.g. Mt. St. Helens before big eruption in
1980
Mt. St. Helens
Plinian Eruption
- named after eruption of Vesuvius
observed by Pliny the Younger
- most powerful eruption type
- explosive ejection of viscous lava
- 10s of miles into the air (stratosphere)
- 100s of miles fallout area
- pyroclastic flows
- large amounts of lava  caldera
forming
- e.g. Krakatoa, St. Helens, Pinatubo
Pinatubo
Methods for Predictions
Predictions of Eruptions
very difficult
complex systems, highly non-linear
every volcano is different
significant progress in recent decades
mostly by continued extensive monitoring
can in many cases predict imminent (~days) eruptions
combinations of different methods used
Methods for Predictions
Seismic (earthquakes, tremors):
short-period earthquakes
like normal fault generated earthquakes
indicate moving lava
long-period earthquakes
indicate increased gas pressure
harmonic tremors
indicate magma pushing on overlying rock
increasing seismic activity  increasing probability of eruption
but complex behaviour
Methods for Predictions
Gas Emissions:
Magma rises  gas escapes
amount and chemical composition monitored
e.g. increase in escaping gas volume observed before
Pinatubo eruption
e.g. decrease of escaping gas volume  sealing of gas
passages  increase in pressure  higher eruption risk
Methods for Predictions
Ground deformation:
moving magma changes pressure inside the mountain
 change in the slopes on the outside
measured e.g. with tiltmeters (laser)
Thermal Monitoring:
IR maps to observe changes in surface temperature
on-side detectors or satellite based
Many major volcanos are monitored extensively to
predict eruptions. These are volcanos in populated areas
and potentially very dangerous ones (Yellowstone).
Dangers of Eruptions
Effects/Dangers
Local (a few 10s of km‘s):
explosions
pyroclastic flows
lava
lahars
gases (CO2, H2S, SO2)
earthquakes
Effects/Dangers
larger scales (10s to 1000s of km‘s):
acid rain (covered earlier in course)
SO2  H2SO4
tsunamies (covered later in course)
ash-fallout
global scales:
volcanic winter, drop in temperatures due to change in
albedo of Earth‘s atmosphere
 crop failure, hunger, conflicts .....
Effects/Dangers - Examples
on average all volcanos on Earth eject 1.3-2.3*1011kg CO2/yr
all human emissions add up to about 2.5*1013kg/yr
Mt. Pinatubo eruption (15.6.1991)
>490 years after last known eruptive activity
2nd largest eruption in 20th century
1013kg of magma ejected up to 34km high
2*1010kg SO2 ejected
coincided with typhoon Yunga  Lahars
ash cloud 125000km2
10 times bigger eruption than Mt.St.Helens on 18.5.1980
~800 people died, mostly due to roofs collapsing
Effects/Dangers - Examples
Effects/Dangers - Examples
Effects/Dangers - Examples
Supervolcanos:
huge off-scale earthquakes
tsunamies
up to several 1000km3 ejecta!
immediate continent scale devastation
mass extinction!!!
next one due? Yellowstone
Effects/Dangers - Examples
Topics to Discuss in Seminar
How to prevent danger for a large number of people in the first place?
How to react in case of an imminent eruption?
don‘t panic
How to react in case of an eruption?
run