sign in sign up
<<
Home , Supervolcano

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 . 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 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 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. 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 production eruption of a 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) (b) hot spot (b) mid-ocean ridge Reducing the risk basaltic,andesitic beneath the other at a “ zone”. Deep within the Earth,the and rhyolitic 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 ),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 Global Positioning System (GPS) can be used to monitor this.Changes in Table 1 - Volcano Explosivity Index are in place to limit building within the vicinity of a volcano and inhabitants are flux and composition can be useful in monitoring the Volcanoes produce: given regular training and made aware of safety procedures. progress of magma evolution as it rises. ■ VEI Tephra Height of eruption Eruption rate Duration Remarks Lava flows volume (m3) column (km) (kg/sec) of blast (hrs) ■ Ash,and “tephra”(larger fragments including lava bombs) 0 <10,000 <0.1 100-1000 <1 Non explosive ■ Mt St Helens:economic losses c.US$1.3bn However, many large volcanoes capable of affecting global climate are in remote parts of the world,and the precursor events may go unnoticed. ■ Pyroclastic flows(mixtures of hot gas and tephra that flow at high speeds) 1 10,000 - 1 million 0.1-1 1000-10,000 <1 Small ■ Rabaul:insured losses c.US$20 million Only a few hundred volcanoes are monitored.The use of satellite ■ Lahars (slurry flows of ash and tephra mixed with water) 2 1-10 million 1-5 10,000-100,000 106 Moderate ■ Ruapehu:economic losses c.US$100 million technology is beginning to increase our ability to monitor remote volcanoes 3 10-100 million 3-15 100,000-1million 1012 Moderate -large ■ Montserrat: estimate costs c.US$150 million - and to monitor others more safely. Even fast-flowing lava rarely kills anyone, though it can cause serious 4 100 million - 1 billion 10-25 1million - 10 million 6-12 Large damage to property. In remote areas gradual ash fallout is also not 5 1-10 billion >25 10-100 million >12 V. Large In less developed countries the cost is human more than financial. Even in particularly deadly, but where there is housing it can cause casualties. For 6 10-100 billion >25 100 million - 1 billion >12 V. large Europe we cannot afford to be complacent. There is a threat to Rome from example, 300 people died around Mt Pinatubo (1991) as a result of ash 7 100 billion - 1 trillion >25 >1 billion >12 V. large Alban Hills volcano where there is evidence of recent uplift over the past few Problems of prediction overloading roofs and causing collapse. 8 >1 trillion >25 >1 billion >12 V. large decades.One of the biggest potential geohazards threatening Europe currently sits quietly overlooking the Bay of Naples. Understanding the mechanisms of each volcano’s eruptive activity enable However, explosive volcanoes also give rise to pyroclastic flows - At the upper end of the Volcanic Explosivity Index we find the largest volcanologists to forecast the way in which the eruption will develop. superheated clouds of ash and hot gas that can move at hurricane velocity eruptions that are sometimes informally known as “supervolcanoes”. Mt Vesuvius has erupted more than 50 times in the last 2000 years. An However no volcano follows a rigid timetable,and “prediction”(that a (100-150km/hr) hugging the ground and destroying everything in their path. eruption in 1631 killed 4000 people,and it last erupted in 1944.When particular event will happen at a certain time) is likely to remain elusive, at A series of pyroclastic flows finally wiped out Pompeii and Herculaneum in One of the most famous historical eruptions,that of Krakatoa (, Vesuvius erupts again (records suggest an eruption is overdue) 800,000 least in the foreseeable future, for most volcanoes. the AD79 eruption of Vesuvius. 1883) only rated 6 on the VEI. The nearest thing to a supervolcano to have residents would have to be evacuated at a cost currently estimated at affected the Earth in historic time is the Tambora eruption (1815, Indonesia) US$100bn. If the eruption were of the same scale as that of AD79,the largest 3 Volcanologists working in observatories,and others who advise on hazard Other volcanic-related hazards include: which rated 7 on the VEI. This eruption put 100km of rock dust and 200 city in southern Italy would be completely devastated and possibly rendered assessment,tread a thin line between fair warning and crying wolf. ■ (see Note 6 in this series) million tonnes of sulphuric acid into the atmosphere. This lowered global uninhabitable for some years. There would be a continuing refugee and temperatures and gave rise to the “year without a summer”(1816), However it is clear from successful interactions between scientists and ■ Earthquakes (see Note 1 in this series) humanitarian crisis that would affect every country in the European Union. widespread famine,and disease. local authorities that openness, frequency of communication and the direct ■ Poisonous gases engagement of the local population are vital for successful civil defence. It is 20 years since Mt St Helens erupted,covering much of Washington State in ■ Climate change However, for the last VEI 8 eruption we have to travel back in time to the fine grey dust. It is even longer since the Fissure (Iceland) created a This is an area where geoscientists’ work is clearly vital to the saving of eruption of Toba,Indonesia (73,500 years ago).The climatic effects of this Europe-wide climatic disaster (1783). The eruption continued for two months, life,but their advice can only be useful if the authorities are properly scale of eruption go much further than a few bad summers. Toba threw an killing a fifth of Iceland’s population (mainly by secondary health effects). The 3 prepared to receive it. In such areas the population will be well drilled and estimated 6000km of material and up to five billion tonnes of sulphuric climate change it caused was noted all over Europe,and if a similar eruption Some historic eruptions will know what to do in the event of an eruption. However many acid into the atmosphere.Global light levels reduced and world were to happen today it would wreak havoc - especially with worldwide air 0 populations around volcanoes are blasé and fatalistic,and motivating them temperatures were estimated to have dropped between 3-5 C causing a travel. The climatic effects of the eruption were similar to those created by the In 1902,all but two of the 29,000 inhabitants of St.Pierre,the capital of to take appropriate measures to protect themselves is not an easy task for that lasted many years. 1815 Tambora eruption; 1784 was noted for having “no summer”,and Martinique (Caribbean) were killed by pyroclastic flows.The burning hot authorities. contemporary records show that death-rates rose in the years following. gases killed them all within a few seconds. Although supervolcano eruptions are huge,they are infrequent; but they will happen again.Their environmental effects rival those of a large asteroid or Volcanologists use laser In 1991 the threat of a from Mt Pinatubo (Luzon island, comet impact,and will put the survival of the human race (if it still exists by rangefinding equipment Philippines) resulted in the evacuation of c.250,000 people.Pinatubo was a then) in jeopardy. major with large numbers of pyroclastic falls and ash There are at least 1500 to measure the slightest falls. movement of volcanic Many volcanoes have active volcanoes on Earth centres. The ash and lava thrown into the atmosphere during an eruption may cause large ice caps, This intense thunder and lightning.Frequently accompanied by heavy rain,this glacier is flowing from and more than 500 million people Photo courtesy, can lead to great loss of life by causing floods, landslides and rivers of mud the summit of Mt Rainier, The Open University (lahars) that wash downhill covering towns and villages.When the Nevado near Seattle,Washington live near enough to be directly del Ruiz (Colombia) volcano erupted (1985) 23,000 people were killed by State, USA. the resulting mudflows - caused not by rain,but by the sudden melting of affected by their eruptions. the volcano’s summit ice cap. The flow buried Armero (see Note 3 in this Photo - Ted Nield series) and neighbouring towns.