VOLCANOES
‘A hill or mountain made from lava and
other erupted material’
The main types
Where do volcanoes occur?
U.S. Volcanoes and Current
Activity Alerts
http://volcanoes.usgs.gov/
Where do volcanoes occur?
Credit: U.S. Geological survey
NAME PROBLEMS
There can be some confusion with the names given to the
various examples of volcanoes.
Named Volcanoes
An older, but still widespread way of naming volcanoes
is to use a particular one as the ‘type’ example.
For Example: Pelean
Plinian (Vesuvian)
Strombolian
Vulcanian
Krakatoan
etc
Sequence of Violence
Hawaiian – low viscosity basaltic lava, gas easily released, gentle
eruptions, little tephra. (Fissure/Shield volcanoes)
Strombolian – More viscous. Gas released regularly in small
explosions.
Vulcanian – Larger explosions, with large clouds of tephra and gas
being produced. Andesitic magma.
Vesuvian – More explosive still, with huge clouds spreading
tephra over large areas.
Plinian – Extremely violent Vesuvian eruptions. Huge amounts of
tephra/removal of cone. AD 79 – Pliny described it
Sequence of Violence (contd)
Krakatoan – The most violent. Most of the volcano was
blown away in 1883 due to sea water entering
magma chamber. Heard 5000 km away. Ash
cloud reached 80 km. Tidal waves killed 36,000.
Pelean – Produce pyroclastic flows from sides of volcanoes
whose vents are choked with very viscous acidic lava.
Mt Pelee in Martinique in the Caribbean in 1902 gave off
a nuee ardente which killed the inhabitants in nearby
St Pierre in a few minutes (about 30,000).
(Eg Mt St Helens – pyroclastic flow at 400 km/hr
reached 26 km away – hot enough to melt plastic!)
Products
It is probably easier to simply describe the main products
produced by a particular volcano – see other slide show.
FISSURE ERUPTIONS
e.g. Fluid basalt lava flows , Mauna Loa, Hawaii
Credit: U.S. Geological Survey
Photograph by J.D. Griggs
Credit: U.S. Geological Survey
Fissure Eruptions
Credit: U.S. Geological Survey
(Photograph by S.R. Brantley)
Credit: U.S. Geological Survey
FLOOD BASALTS
Low viscosity lava can spread over vast areas, building
up vast thicknesses of lava.
Eg: India, Siberia, N America.
The vast quantities of greenhouse gases produced are
thought to have led to mass extinctions at the end of
the Permian period (235 Ma ago) when 95% of life
disappeared, much more than when the dinosaurs
became extinct 140 Ma later.
Submarine Volcanoes - Pillows
Credit: U.S. Geological Survey
(Photograph by R.D. Griggs)
Types of Volcanoes
Reminder: the different volcanic materials that can
be erupted produce different types of volcanoes
Credit: U.S. Geological Survey
(Illustration by J. Johnson)
Shield volcanoes
Volcanoes with broad,
gentle slopes and built
by the eruption of fluid
basalt lava.
Basalt lava flows across
the ground easily to
build enormous, lowangle cones.
Credit: U.S. Geological Survey
The largest volcanoes on Earth are shield volcanoes. (Mauna Loa is
the tallest volcano on Earth, as measured from the sea floor)
Cross section through a shield volcano
Credit: U.S. Geological Survey
A strato volcano
A strato volcano – alternate layers of lava & tephra.
Examples – Vesuvius, Etna, Fuji
Credit: U.S. Geological Survey
Photograph by Lyn Topinka
Strato Volcano
Cross section through
a strato volcano
Credit: U.S. Geological Survey
Plinian Type Volcano
Violent explosion of viscous
magma e.g. Mt Vesuvius
as witnessed by Pliny in AD79.
Credit: U.S. Geological Survey
(Photograph by R. McGimsey
)
Credit: U.S. Geological Survey
Layers of ash covering the area after the
eruption of Mt Pinatubo Phillipines, 1992
Pelean Volcano
Credit: U.S. Geological Survey
(Photographer B. Chonet)
Pelean Volcano – is built up by pyroclastic flows
(est 800 deg C and 160 km/hr.
A classic example was Mt Pelee, Caribbean, 1902
Strombolian
eruptions
Credit: U.S. Geological Survey
(Photographer E Wolfe)
Stromboli is in the Mediterranean. Strombolian eruptions are
discrete explosions (called Strombolian explosions or Strombolian
bursts) of relatively fluid lava from a single vent. It is thought that
they originate when large gas bubbles rising within the conduit burst
at the partly solid surface of the magma column inside the vent.
VOLCANO FILE
Build up your own collection of
volcano data and photographs.
There might be one during this course –
there was last year!