Peter Copley Feb 04

VOLCANOESVOLCANOESTheirTheir

ProductsProducts

Peter Copley Feb 04

Types of Types of Lava Lava

Aa - blocky (no gas/viscous)Pahoehoe – ropy (fluid)

Peter Copley Feb 04

MAGMA COMPOSITIONMAGMA COMPOSITION

‘Acidic’ – high silica, low temperature (~ 800 deg C), viscous. eg Andesite, Rhyolite

Gases are trapped, violent explosions, pyroclastics.

‘Basic’ – low silica, high temperature (~ 1200deg C), fluid. eg Basalt Gases can escape, gentle eruptions, lava

Peter Copley Feb 04

ASH ASH CLOUDCLOUD

Mount St Helens, WashingtonPinatubo, Phillipines

Credit: U.S. Geological Survey Credit: U.S. Geological SurveyCredit: U.S. Geological Survey

Peter Copley Feb 04

PyroclasticPyroclasticFlowFlow(Nuee(NueeArdente)Ardente)

Very hot (~1000 deg C)Ash and volatiles. Flows very fast.

Rock formed is anIgnimbrite ( egSnowdonia)

Credit: U.S. Geological Survey

Peter Copley Feb 04

TEPHRATEPHRA

A general A general termtermto includeto includeash, lapilli,ash, lapilli,blocks &blocks &bombsbombs

Credit: U.S. Geological Survey

(Photographs: 1 - D E Wieprecht; 2 - C Heliker)

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Peter Copley Feb 04

Volcanic Ash – less than 2mmVolcanic Ash – less than 2mm

Lapilli – 2 to 64 mmLapilli – 2 to 64 mm

Volcanic bombs – more than 64mmVolcanic bombs – more than 64mm

Terms used to describe tephraTerms used to describe tephra

Peter Copley Feb 04

Pumice – volcanic frothPumice – volcanic froth

Peter Copley Feb 04

Some ‘volcanic’ termsthat you should become familiar with.

Credit: U.S. Geological Survey

Peter Copley Feb 04

LAHARSLAHARS When pyroclastic debris gets mixed withwater (eg rain, melted ice or snow) it produces a fast flowing mud flow.This can be very destructive flowingdown valleys and submerging settlements.

Nevada de la Ruiz, Colombian Andes, 1985. The town of Armero, 50 km away, was engulfed, killing 25,000 people.Credit: U.S. Geological Survey

(Photographs: 1 – B Myers; 2 – JN Marso

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Peter Copley Feb 04

Peter Copley Feb 04

Mount St Helens Eruption, 1980 – photo sequence

Credit: U.S. Geological Survey

Peter Copley Feb 04

Effect of blast from Mt St Helens

These trees were about 30 km away!

Credit: U.S. Geological Survey(Photograph by Lyn Topinka)

Peter Copley Feb 04

Peter Copley Feb 04

A Caldera Caused by the collapse of a volcano into its magma chamber. This one is several miles across.

Credit: U.S. Geological Survey(Photograph by M Williams)

Peter Copley Feb 04

A Geyser (from the Icelandic – Geysir).Water moves down to the hot rock or magma which turns to superheated steam. When the pressure is sufficient it rapidly expands and reaches the surface as a column of very hot water and steam.

HYDROTHERMALEFFECTS

Credit: U.S. Geological Survey(Photograph : SR Brantley)

Geyser at Yellowstone National Park, Wyoming

Peter Copley Feb 04

VOLCANIC GASESVOLCANIC GASES

Water vapour (70 – 95%) – origin of oceansCarbon dioxideSulphur dioxide

Peter Copley Feb 04

Effect on ClimateEffect on ClimateGlobal Warming – most volcanic gases produce a greenhouse effect.

Global Cooling – pyroclastic debris can block out the Sun. 1992 – Pinatubo a 0.5 deg C drop

1815 – Tambora (Indonesia) ‘the year without a summer’.

Peter Copley Feb 04

I suggest that you go on I suggest that you go on the Internet and find some the Internet and find some of your own images. I got of your own images. I got most of these from Google most of these from Google (images).(images).