4 4 bout these briefings he where, when and how of volcanoes Volcanic eruptions are T spectacular and A dangerous. Their effects Published by: can be local or global. The Earth is a dynamic planet. It is active Geoscientists also help to minimise hazards The Geological Society of London Volcanoes occur Large eruptions can affect Burlington House and productive, offering humanity we have created (or made worse) by our weather patterns Piccadilly enormous opportunities. However, living on activities. These include subsidence, and ■ worldwide and may LONDON W1J 0BG At or near boundaries of tectonic plates. cause climate change. it also presents us with many dangers; the disposal of waste. Tel:+44 (0)20 7434 9944 some of our own making. Fax:+44 (0)20 7439 8975 ■ Within tectonic plates, as a result of ‘hot spots’ where plumes of hot material There are at least 1500 With their unique understanding of the Email:[email protected] rise from deep within the Earth, probably from the boundary between the Earth’s active volcanoes on Earth In our interaction with the Earth, immensely long time spans over which Web site:www.geolsoc.org.uk mantle and its core. and more than 500 geoscientists are in the front line. They Earth processes operate, geoscientists help © The Geological Society of London. million people live near Any part of this document may be enough to be directly seek and find the raw materials we use for communities world-wide to learn how to Most volcanoes, whether on land or at sea, are located at or near plate boundaries agriculture, roads, buildings,energy, water use the planet’s resources safely, wisely, reproduced free of charge,but with affected by their acknowledgement. eruptions. The most supply and all the industries that provide and sustainably. (Figs. 1,2). Beneath the oceans, crustal plates move apart and new oceanic crust heavily populated areas Further copies are available on request wealth and health. forms at spreading centres along oceanic ridges such as the Mid-Atlantic Ridge. are generally in the (preferably by email). Individual copies This series of information sheets is poorer regions of the are free,and will be posted anywhere Volcanoes erupt lava into the widening crack, which then cools to form new ocean world, though the Geoscientists help society understand dedicated to bringing this role to public without charge. Multiple copies attract floor. Iceland is an example of a spreading-centre volcanic landmass, located on the economic losses that natural hazards and mitigate their effects. attention. both charge and postage. Please would result from an Such dangers include floods,landslips, contact the Society if you wish to order Mid-Atlantic ridge (above a region of higher than normal magma production eruption of a volcano more than one copy. volcanic eruptions and earthquakes. - a “hot spot”). near a major city (such as Series Editor: Ted Nield Mt Rainier, (Seattle) or Written by: Cally Oldershaw When continents begin to break apart, a chain of active volcanoes form in “rift Vesuvius, (Naples)) Further information and useful contacts would be immense. The Geological Society gratefully valleys” such as in the East African Rift. Some of the biggest volcanoes in Africa are acknowledges the assistance of the Web sites Printed information situated on the shoulders of the Rift Valley e.g., Mt Kenya, Mt Elgon, Mt Kilimanjaro Even where tales of following scientists,who (in a personal disaster are still fresh in www.geolsoc.org.uk useful links,up to date information, Bell,F G 1999 Geological hazards:their assessment, capacity as Fellows of the Society) read and Mt Meru. At divergent margins, basaltic volcanoes,with hot, runny lava, erupt the memories of fact sheets and historic data including photographs and avoidance and mitigation (E & F N Spon,London.648 pp) and commented on earlier drafts of this gently because gases can escape easily without causing explosions. survivors, people soon video images. briefing. McGuire, W Violent Earth:the threat from geohazards return to live on volcano www.volcanoes.usgs.gov/ US Geological Survey Volcano (The Geological Society/Benfield Greig Hazard Research Dr Hazel Rymer Fig. 1 - Volcanoes of the world, related to plate boundaries flanks. This is often Hazards Program homepage has weekly reports of Centre Leaflet,2000) Prof.Chris Wilson (Honorary Secretary, because of the scenic worldwide volcanic activity and regularly updated feature McGuire, W J 1997. Volcanic disasters:past,present, Foreign & External Affairs) beauty of the area and stories. North American increased fertility of the and future. Science Progress 80 (1),pp 83-99. Prof.Bill McGuire Plate soil, but also because for www.bghrc.com Benfield Greig Hazard Research Centre Dr Clive Oppenheimer Eurasian Eurasian McGuire, WJ & Kilburn,C R J 1997: Forecasting volcanic Plate Plate many there is simply (University College London) homepage. Dr David Pyle events:some contemporary issues. Geol.Rundschau 86, Juan de Fuca nowhere else to go. Prof.Steve Sparks Plate Caribbean www.volcano.und.nodak.edu/vwdocs University of 439-445. Plate Phillippine North Dakota home page has the latest information on Arabian Earthwise Issue 14. Geohazards (British Geological May 2001 Plate Cocos volcanic eruptions worldwide.Reports include eruption Plate Survey) The Geological Society of London Pacific Plate descriptions,maps and photographs with a search facility Plate to check on particular eruptions. Rymer, H 1993: Predicting volcanic eruptions using is a Registered Charity, No.210161 African Nazca Plate microgravity, and the mitigation of volcanic hazard.In Indian South American www.explorezone.com/news/volcanoes.htm Plate Plate Plate Natural Disasters.Protecting Vulnerable Communities Volcano news zone is part of the Earth zone of this easy (Thona Telford,London) 252-270 to use Earth science web site.There is a good introduction to volcanoes,a search facility and useful links. Rymer, H 2000. Living with Volcanoes. Geology Today Antarctic Plate Scotia 16 (1) 26-31 www.learner.org/exhibits/volcanoes/entry.html Plate In addition to a comprehensive introduction on volcanoes, the site has information on judging hazards, forecasting and coping with risk. divergent plate boundary convergent plate boundary transform fault plate boundary volcanoes Designed &Produced by Witherbys 020 7253 5413 Website: www.witherbysonline.com Continental Crust Where plates move toward one another (converge),the denser plate sinks (a) volcanic arc (b) hot spot (b) mid-ocean ridge Reducing the risk basaltic,andesitic beneath the other at a “subduction zone”. Deep within the Earth,the and rhyolitic lavas basaltic lavas basaltic lavas sinking (subducted) plate releases water, which rocks of the Earth’s mantle Three million people would be at risk if Mt Rainier (picture,bottom left) to melt.Molten rock (magma) rises towards the surface where it pierces the sea level erupted tomorrow. One million people live in the shadow of Vesuvius and over-riding plate and volcanoes form:e.g.,the Andes (South America) and a further million live near the volcano of Popocatepetl (near Mexico City). the Cascade Mountains (NW United States),and many arc-shaped chains of volcanic islands,such as those in the Western Pacific (including Japan). partial The study of a volcano’s historical eruptions - by mapping their various melting rock products - is vital to assessing the level and nature of likely hazards The water makes subduction-zone volcanoes more explosive than those in surrounding areas,providing the basic information for “hazard maps”. water sited far from plate margins,and because the magma contains more silica it hot spot These form the basis of evacuation and other civil defence procedures that is more viscous (sticky).Huge pressure traps gases in solution in the authorities need to put into effect. magma.When the pressure is released,the gases come out from the dehydration of oceanic crust Ocean Crust Mantle solution and escape at the surface in (occasionally huge) explosions. Warning signs Fig. 2:How volcanoes coincide with different types of plate margin Photo - Ted Nield In 1980 at Mt St Helens (Cascade Mts) a landslide (see Note 3 in this Volcanic eruptions rarely come unheralded,which allows some warning to series) on the volcano’s flank released the confining pressure. Gases in the be given - if the volcano is under scientific scrutiny. magma suddenly came out of solution and created a gigantic explosion that spread ash over a wide area. The typical grey ash of these eruptions is Monitoring methods produced as the molten rock is blown apart by escaping gases and cools in the atmosphere. Supervolcanoes Counting the cost Volcanoes are monitored using earthquake sensors (seismometers) and gravity meters that can track the movement of magma and gas to the Many of the world’s most explosive volcanoes lie around the margin of the Like earthquakes,volcanic eruptions are classified on a numerical scale Size, type of eruption and location are the most significant factors affecting the surface. Volcanoes often swell over months and years as they build up to Pacific Ocean (the “Ring of Fire”).Because many are surrounded by heavily based on their explosivity - the Volcanic Explosivity Index (Table 1). ultimate cost of a volcanic eruption.In advanced but densely populated an eruption,and sensitive tiltmeters,laser rangefinders (picture) and the populated areas they cause great loss of life. countries like Japan,where volcanic activity is a regular occurrence,procedures