GeoActiveGeoActive 432 OnlineOnline WHAT IS A SUPERVOLCANO? by John Davidson HE TERM supervolcano Twas first used in the year 2000 to describe a small number of giant volcanoes that have D E produced rare but catastrophic Yellowstone G Long Valley eruptions. Somewhere in the Campi Flegrei Aso world a supervolcano erupts C roughly every 50,000 to 100,000 A Toba years and blasts over 1,000 B F cubic km (km3) of material into the air. Supervolcanoes are very Taupo large and usually 50 to 100 km in diameter. Figure 1 shows H the location of the world’s Key known supervolcanoes. Some Supervolcano eruption in the last 2 million years supervolcanoes are located in Figure 1: World distribution of supervolcanoes areas of dense human population, in South-east Asia, western USA, Japan and Italy, and they have Supervolcano Country GeoActiveDate Series of 21 eruption Issue 2 Volume of ejected 3 attracted considerable interest Fig 432_01 Mac/eps/illustrator(years before 11 s/s material (km ) NELSON THORNESpresent) PUBLISHING from geographers and geologists Artist: David Russell Illustration because they are potentially Long Valley USA 760,000 560 very dangerous and not fully caldera, California understood. The dates of historic Lava Creek, USA 640,000 1,000 supervolcano eruptions in the Yellowstone last million years are shown in Whakamaru New Zealand 254,000 2,000 Figure 2. As no supervolcano has Aso Japan 80,000 600 produced a full-scale eruption in Mount Toba, Indonesia 74,000 2,800 the last 2,000 years, we can only Sumatra work out from rocks and fossils Campi Flegrei Italy 39,000 500 how extreme their eruptions can Lake Taupo New Zealand 26,500 1,170 be. Figure 2: Dates of historic supervolcano eruptions Geologists classify volcanoes into eight types using the How do supervolcanoes rather like air rushing out of a Volcano Explosivity Index (VEI), erupt? balloon that has been burst. which is based on the types Geologists believe that beneath 2 The pressure from the rising of eruption (Figure 3). Runny each supervolcano there is a bubble of magma underneath lava (Hawaiian-type) volcanoes very large bubble of very sticky literally pushes off the lid of found along mid-ocean ridges let magma tens of kilometres across. overlying rock, in the same gases escape easily. Cone-shaped This bubble of magma becomes way that floodwater in an composite volcanoes found along trapped under overlying rock, underground drain can lift up destructive plate boundaries with water vapour, carbon manhole covers in a road. With have sticky lavas and produce dioxide and sulphur dioxide the overlying lid gone, the whole explosive eruptions graded trapped within it. magma bubble bursts out. from 2 to 7. Supervolcanoes are 3 A sudden drop in pressure, graded VEI 8, the most explosive Supervolcanic eruptions may be produced as the magma nears category. Figure 4 shows the main started in three ways: the surface, may cause dissolved differences between a composite 1 An earthquake cracks the rock gases in the liquid magma to volcano and a supervolcano. above it and suddenly releases be released from solution. the magma which explodes out, The whole magma mass then Series 21 Spring issue Unit 432 What is a Supervolcano? © 2010 Nelson Thornes GeoActive Online This page may be photocopied for use within the purchasing institution only. Page 1 of 4 VEI Classification Description Height of ash Amount of material Example plume ejected 1 Hawaiian Non-explosive/ 100–1,000 metres Less than 1 million m3 Mauna Loa, Hawaii gentle 2 Strombolian Explosive 1–5 km 1 million to 10 million Stromboli, Italy m3 3 Vulcanian Severe explosive 3–15 km 10 million m3 to 0.1 Vulcano, Italy km3 4 Pelean Cataclysmic 10–25 km 0.1 km3 to 1 km3 Mount Pelée, Martinique 1902 5 Plinian Paroxysmal Over 25 km 1 km3 to 10 km3 Mount St Helens, USA 1980 6 Ultra-Plinian Colossal Over 25 km 10 km3 to 100 km3 Mount Pinatubo, Philippines 1991 7 Ultra-Plinian Super-colossal Over 25 km 100 km3 to 1,000 km3 Tambora, Indonesia 1815 8 Supervolcano Mega-colossal Over 25 km Over 1,000 km3 Mount Toba, Sumatra, 74,000 years ago Figure 3: Volcano Explosivity Index (VEI) becomes a massive explosive COMPOSITE VOLCANO SUPERVOLCANO froth which blasts out of the Example, Mt St Helens ground – rather as a bottle of fizzy drink can explode if it is Main vent shaken very violently. Caldera Layers of ash Possible and lava side vents Smaller volcano Scientists believe that a or steam eruption/ geyser Rising dome supervolcano produces a massive Lake explosion which literally blasts the crust and molten froth into Local Local rocks rocks the air. Ash is blown over 30 Magma km up into the atmosphere. bubble Faults Some remains airborne for many months, drifting around the Earth and gradually falling like Magma grey snow, but large amounts chamber Rising magma from below collapse back down to Earth Figure 4: Differences between composite volcanoes and supervolcanoes while still very hot and then travel long distances over the amount of material from a ground as pyroclastic flows. What are their effects? descending plate beginsGeoActive to rise Series 21 Issue 2 When all the magma has been Fig 432_04 Mac/eps/illustratorUsing 11 evidences/s such as ash and back up to the surface. This erupted, a deep crater is left NELSON THORNES PUBLISHINfossil remains,G geologists have magma rises up underArtist: the David Russell Illustration behind called a caldera (from the worked out that a supervolcano continental crust and produces a Latin word for cauldron). These eruption could produce the very sticky mass of molten rock depressions are often over 50 following effects: rich in silica. km in diameter, and sometimes 3 fill with water. Figure 5 shows 2 Above continental ‘hotspots’ • Between 1,000 and 3,000 km an example of such a depression where a large bubble of rising of ash are blasted up into the as a cross-section through the magma is pushing up through atmosphere. Long Valley caldera in the Sierra the plate and heating the • Ash fall between 1 and 5 metres Nevada mountains east of San continental crust. deep can occur up to 1,000 km Francisco. Figure 6 show how from the supervolcano. In both these cases, the crust supervolcano eruptions compare • The cloud of ash can block out is being extended locally with more recent volcanic events. solar radiation causing a ‘volcanic or ‘stretched’, producing winter’, which may last from one weaknesses that allow the magma How and why do to five years. Estimates suggest bubbles (sometimes called supervolcanoes form? worldwide falls in temperature plumes) to rise up towards the of between 5° and 10°C, possibly Supervolcanoes mainly occur in surface over a long period of resulting in an ice age. areas of continental crust in two time. This steady flow of hot types of location: rock over thousands of years • The explosive eruption could 1 Near destructive plate forms the large magma lakes destroy everything within a boundaries where a large beneath supervolcanoes. radius of 500 km. Series 21 Spring issue Unit 432 What is a Supervolcano? © 2010 Nelson Thornes GeoActive Online Page 2 of 4 This page may be photocopied for use within the purchasing institution only. Caldera Case Study Mammoth Mountain Glass Mountain Dome Yellowstone Deposits of ash/lava The Yellowstone caldera is Faults located in the north-west corner Faults Solid magma 5 km of the state of Wyoming in the USA and measures 55 km by Rising magma 10 km 72 km. Yellowstone lies over bubble a hotspot where a large mass of magma is rising up from 15 km the mantle. The Yellowstone supervolcano has erupted at 20 km least twelve times in the last 15 million years, at regular intervals Rising magma of about 600,000 years. The last supervolcano eruption was Local extension (stretching) of crust 640,000 years ago. Previous Figure 5: Cross-section through a caldera (Long Valley, California) eruptions have produced a blast zone of 1,000 km and ash fall up GeoActive Seriesto 21 1,600 Issue 2km from Yellowstone Volcano Country Date Volume ofFig material 432_05 Mac/eps/illustrator (see Figure 11 s/s8) and today 20 ejected (kmNELSON3) THORNES PUBLISHING Artist: David Russellmillion Illustration people live within Mount St Helens, USA 1980 0.25 1,000 km of the supervolcano. Washington COMPOSITE VOLCANO SUPERVOLCANO Earthquakes occur frequently Mount PinatuboExample, Mt StPhilippines Helens 1991 5 and Yellowstone is swelling Tambora Indonesia 1815 160 by 1–3 cm every year, which Campi Flegrei Main venItalyt 39,000 years ago 500 may indicate increasing magma Caldera Long Valley USA 760,000 years ago 560 pressure below. The Yellowstone Layers of ash Possible caldera,and lava California side vents Smaller volcano Volcano Observatory will issue or steam eruption/ warnings based on earthquake geyser Rising dome Lava Creek, USA 640,000 years ago 1,000Lake Yellowstone readings if an eruption is believed to be imminent and Lake Taupo New Zealand 26,500 years ago 1,170 Local Local the State of Wyoming has rocks rocks Mount Toba, Indonesia 74,000 years ago Magma 2,800 evacuation plans in place, but Sumatra bubble Faults a supervolcano eruption here Figure 6: Comparison of supervolcano eruptions and some recent eruptions could destroy much of the farming across the USA, and • An erupting Magmasupervolcano on earthquakes and the changing make large areas of the continent Rising magma from below the coast couldchamber trigger massive shape of the volcano, but it is uninhabitable. wave surges (tsunamis) which difficult to predict precisely may travel up to 5,000 km.