VOLCANOES The main types ‘A hill or mountain made from lava and other erupted material’

Where do volcanoes occur? U.S. Volcanoes and Current Activity Alerts

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 Credit: U.S. Geological Survey Photograph by J.D. Griggs e.g. Fluid basalt lava flows, Mauna Loa, Hawaii 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, low- angle 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 – alternate layers of lava & tephra. Examples – Vesuvius, Etna, Fuji A strato volcano Credit: U.S. Geological Survey Photograph by Lyn Topinka

Strato Volcano Cross section through a strato volcano Credit: U.S. Geological Survey

Violent explosion of viscous magma e.g. Mt Vesuvius as witnessed by Pliny in AD79. Plinian Type Volcano Credit: U.S. Geological Survey (Photograph by R. McGimsey )

Layers of ash covering the area after the eruption of Mt Pinatubo Phillipines, 1992 Credit: U.S. Geological Survey

Pelean Volcano – is built up by pyroclastic flows (est 800 deg C and 160 km/hr. A classic example was Mt Pelee, Caribbean, 1902 Pelean Volcano Credit: U.S. Geological Survey (Photographer B. Chonet)

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. Strombolian eruptions Credit: U.S. Geological Survey (Photographer E Wolfe)

VOLCANO FILE Build up your own collection of volcano data and photographs. There might be one during this course – there was last year!