PH307 Disasters: VolcanosDr. 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

Olympus Mons (Mars)

Mauna Loa

Skjaldbreidur Mt. Edziza

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. St. Helens Popocatépetl

Mt. Fuji Stromboli

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

Yellowstone Caldera

Lake Taupo

Campi Flegrei

SupervolcanosMt. Aso

Type of Eruptions

Eruption Types

Subglacial

Strombolian

Vulcanian

Peléan

Hawai‘ian

Phreatic

Plinian

Subglacial Eruption

Subglacial eruption: 1 water vapor cloud, 2 lake, 3 ice, 4 pillow lava, 5 magma conduit, 6 magma chamber

- under ice or glacier

- risk of floods, lahars

- rare type (only 5 active)

- e.g. Iceland

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

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

- 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

Peléan Eruption

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

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)

Hawai‘ian Eruption

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

- 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

Phreatic Eruption

Mt. St. Helens

- 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

Plinian Eruption

Pinatubo

- 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

Methods for Predictions

Predictions of Eruptions

very difficultcomplex systems, highly non-linear

every volcano is different

significant progress in recent decadesmostly 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