1. VOLCANOES
Their
Products
Peter Copley Feb 04

2. Types of Lava Aa - blocky (no gas/viscous) Pahoehoe – ropy (fluid)
Peter Copley Feb 04

3. MAGMA 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

4. ASH CLOUD Mount St Helens, Washington Pinatubo, Phillipines
Credit: U.S. Geological Survey
Credit: U.S. Geological Survey
Credit: U.S. Geological Survey
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5. Pyroclastic Flow (Nuee Ardente)
Very hot (~1000 deg C)
Ash and volatiles.
Flows very fast.
Rock formed is an
Ignimbrite ( eg
Snowdonia)
Credit: U.S. Geological Survey
Peter Copley Feb 04

6. TEPHRA A general term to include ash, lapilli, blocks & bombs1
TEPHRA A general term to include ash, lapilli, blocks & bombs 2 3
Credit: U.S. Geological Survey
(Photographs: 1 - D E Wieprecht; 2 - C Heliker)
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7. Volcanic Ash – less than 2mm
Terms used to describe tephra
Volcanic Ash – less than 2mm
Lapilli – 2 to 64 mm
Volcanic bombs – more than 64mm
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8. Pumice – volcanic froth
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9. Some ‘volcanic’ terms that you should become familiar with.
Credit: U.S. Geological Survey
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10. LAHARS When pyroclastic debris gets mixed with
water (eg rain, melted ice or snow) it
produces a fast flowing mud flow.
This can be very destructive flowing
down valleys and submerging settlements.
Nevada de la Ruiz, Colombian Andes, 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 1 2
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11. Peter Copley Feb 04

12. Mount St Helens Eruption, 1980 – photo sequence
Credit: U.S. Geological Survey
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13. Effect of blast from Mt St Helens
These trees were about 30 km away!
Credit: U.S. Geological Survey
(Photograph by Lyn Topinka)
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14. Peter Copley Feb 04

15. 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

16. HYDROTHERMAL EFFECTS 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.
Geyser at Yellowstone National Park, Wyoming
Credit: U.S. Geological Survey
(Photograph : SR Brantley)
Peter Copley Feb 04

17. VOLCANIC GASES Water vapour (70 – 95%) – origin of oceans
Carbon dioxide
Sulphur dioxide
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18. Effect on Climate
Global 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

19. I suggest that you go on the Internet and find some of your own images
I suggest that you go on the Internet and find some of your own images. I got most of these from Google (images).
Peter Copley Feb 04