Landforms at plate margins- volcanoes and supervolcanoes

1. Landforms at plate margins- volcanoes and supervolcanoes • Learning Objectives: • To know why people continue to live near volcanoes • To know how volcanoes are formed and the difference between a shield and composite volcano

2. STARTER: Why do people choose to live near volcanoes? 60 million people continue to live near or on dangerous volcanoes despite volcanoes often claiming many lives. e.g. volcanic areas offer a variety of attractions for tourists, including bathing in the hot springs and mud pools, watching geysers, volcano walking up to and around the equator.

3. This lava is weathered (broken down) to form a fertile soil. Tourists are attracted to areas of volcanic activity. Geothermal energy can be produced in many volcanic areas. Why do people live in volcanic areas? Can you think of any other reasons?

4. Volcanoes have a wide range of effects on humans. These can be problematic or beneficial. However, many people rely on volcanoes for their everyday survival. Today, many millions of people live close to volcanoes for this very reason. Volcanoes attract millions of visitors (tourists) around the world every year. Apart from the volcano itself, hot springs and geysers can also bring in the tourists. This creates many jobs for people in the tourism industry. This includes work in hotels, restaurants and gift shops. Often locals are also employed as tour guides. People live close to volcanoes because Geothermal energy can be harnessed by using the steam from underground which has been heated by the Earth's magma. This steam is used to drive turbines in geothermal power stations to produce electricity for domestic and industrial use. Countries such as Iceland and New Zealand use this method of generating electricity. Why do people live close to volcanoes? Lava from deep within the earth contains minerals which can be mined once the lava has cooled. These include gold, silver, diamonds, copper and zinc, depending on their mineral composition. Often, mining towns develop around volcanoes. Volcanic areas often contain some of the most mineral rich soils in the world. This is ideal for farming. Lava and material from pyroclastic flows are weathered to form nutrient rich soil which can be cultivated to produce healthy crops and rich harvests. Remember poor countries such as this rely on farming as a way of life.

6. Hot spots

7. http://www.bbc.co.uk/news/world-europe-17700377 Ash, cinders, pumice, dust, gas and steam What is a volcano? A volcano is a cone-shaped mountain formed by surface eruptions from a magma chamber inside the Earth. The magma that reaches the surface in an eruption is called lava.

8. How are volcanoes formed? Volcanoes are formed where magma escapes through a vent, which is a fracture or crack in the Earth’s crust. This happens most often at plate margins. Lava and other products are thrown out from the circular hole at the top called the crater. Each time an eruption takes place, a new layer of lava is added to the surface of the volcano; since more lava accumulates closer to the crater during every eruption, a cone-shaped mountain is formed.

11. Different types of volcano Volcanoes are divided into two main types, depending upon the material thrown out in an eruption and the form (height and shape) of the volcanic cone produced. Along constructive margins the basic lava that has come from within the mantle has a low silica content: it pours out easily, it is runny and flows long distances, building up shield volcanoes. Along destructive margins the acid lava has a high silica content, which makes it more viscous so that it travels shorter distances before cooling; these are more explosive volcanoes. After an eruption the vent becomes blocked, which results in great pressure building up before the next eruption. During explosive eruptions lava is shattered into pieces so that bombs, ash and dust are showered over a wide area.

12. Composite are constructed along subduction zones.  Examples of composite volcanoes include Mount Fugi, and Vesuvius. Alternating layers of lava and rock fragments Composite volcanoes usually erupt in an explosive way.  This is usually caused by viscous magma.  When very viscous magma rises to the surface, it usually clogs the crater and gas in the crater gets locked up. Therefore, the pressure will increase resulting in an explosive eruption.

13. Composite Cone Mt St Helens - USA The volcano is built up of alternate layers of LAVA and ASH. They can explode with great violence. Crater Pyroclastic Flow Ash layer Dyke Lava Layer Flank eruption Conelet Lava Flow Crust

14. Composite (Mt St Helens)

15. SHIELD VOLCANO • Shield volcanoes are huge in size.  They are built by many layers of runny lava flows. Lava spills out of a central vent or group of vents.  A broad shaped, gently sloping cone is formed.  This is caused by the very fluid, basaltic lava which can't be piled up into steep mounds. • The eruptions of shield volcanoes are not very explosive • Famous shield volcanoes can be found for example in Hawaii (e.g. Mauna Loa and Kilauea).

16. Composite Cone Mt St Helens - USA The volcano is built up of alternate layers of LAVA and ASH. They can explode with great violence. Crater Pyroclastic Flow Ash layer Dyke Lava Layer Flank eruption Conelet Lava Flow Crust

17. Shield ( Basic) Cone Mauna Loa Hawaii -USA Shield Volcanoes are enormous features built up only from layers of lava. They produce lots of lava but they tent not to erupt violently. Layers of Lava Lava Flow 10,000m 250 miles Composite volcano to scale

18. Shield volcano (Kilauea)

19. http://www.bbc.co.uk/learningzone/clips/which-gases-are-produced-by-volcanoes/1619.htmlhttp://www.bbc.co.uk/learningzone/clips/which-gases-are-produced-by-volcanoes/1619.html http://www.bbc.co.uk/learningzone/clips/abseiling-into-a-live-volcano/7114.html http://www.bbc.co.uk/learningzone/clips/formation-of-limestone-and-basalt-rocks-on-the-antrim-coast-in-northern-ireland/6682.html http://www.bbc.co.uk/schools/gcsebitesize/geography/natural_hazards/volcanoes_video.shtml

20. Internet links • Volcano World - a fun and informative web sitehttp://volcano.und.nodak.edu/ • Virtual field visits http://educeth.ethz.ch/stromboli/ • TheMichigan Technological University Volcanoes Pagehttp://www.geo.mtu.edu/volcanoes/ • Global Volcanism Programhttp://www.volcano.si.edu/gvp/ • Fallout: Eye on the Volcanohttp://www.nationalgeographic.com/features/98/volcanoes/ • Savage earthhttp://www.pbs.org/wnet/savageearth/

21. What is a supervolcano? Learning Objective: 1) To understand what a supervolcano is and how it differs from a volcano 2) To know the potential impact of a supervolcano eruption in contrast to a volcanic eruption

23. Primary effects- the immediate impact • people injured and killed by falling debris; suffocated by poisonous gases or buried under mud flows after the heat of the eruption melts snow at the top of the volcano. • buildings, homes, property, animals and farmland destroyed. It is many years before the lava weathers into fertile soil that can be used for farming. • communications and public services (roads and transport, electricity, telephones) disrupted • livelihoods lost and people forced to migrate • Secondary effects- the medium and long-term impact • shortages of drinking water, food and shelter • spread of disease from contaminated water • economic problems from the cost of rebuilding and the loss of farmland, factories, tourism and other economic activities • social problems from family losses and stress Loss of life is always more likely in volcanic eruptions along destructive plate margins. Living close to shield volcanoes is safer as lives are rarely threatened when only lava is erupted, even from a composite cone as people have time to move out of the way of the lava flows.

24. Supervolcanoes- are massive volcanoes A supervolcano is a volcano that erupts with a massive volume of material, much more than from a normal volcano- at least 1000km3 of magma. They are very large scale/ mega (colossal) eruptions. In 1980 the big eruption of Mount St Helens, USA produced 1km3. A supervolcanic eruption alters the landscape over hundreds, if not thousands, of kilometres. So much dust is circulating in the atmosphere that it can lead to a ‘volcanic winter’- lower temperatures on Earth (i.e. global cooling) because less sunlight reaches the surface. All the world would be affected. The last known supervolcano eruption was Toba in Indonesia- 75000 years ago. Supervolcanoes do not look like a volcano with its characteristic cones as they have large depressions called calderas, often marked by a rim of higher land around the edges.

25. Yellowstone supervolcano Millions visit the National Park for its surface hot pools and geysers, but how many of them know what lies under the surface and gives the heat? Last eruption- about 2 million years ago. Volcanic ash from this eruption covered more than half of North America. Probability of the next few thousand years is thought to be low.

26. Supervolcanoes are much bigger than standard volcanoes. They develop in a few places around the globe- at destructive plate margins or over parts of the mantle that are really hot (called hotspots) e.g. Yellowstone National Park in the USA is on top of a supervolcano. • How do supervolcanoes form at hotspots? • Magma rises up through cracks in the crust to form a large magma basin below the surface. The pressure of the magma causes a circular bulge on the surface several kilometres wide. • The bulge eventually cracks, creating vents for the lava to escape through. The lava erupts out of the vents causing earthquakes and sending up gigantic plumes of ash and rock. • As the magma basin empties, the bulge is no longer supported so it collapses-spewing up more lava. • When the eruption’s finished there’s a big crater (a caldera) left where the bulge collapsed. Sometimes these get filled with water to form a large lake e.g. Lake Toba in Indonesia. • Supervolcanoes are flat (unlike normal volcanoes which are mountains); cover a large area (much bigger than normal volcanoes); have a caldera (normal volcanoes have a crater). http://www.wwnorton.com/college/geo/egeo2/content/animations/2_6.htm

27. http://www.bbc.co.uk/learningzone/clips/volcanoes-and-global-climate-no-narration/1479.htmlhttp://www.bbc.co.uk/learningzone/clips/volcanoes-and-global-climate-no-narration/1479.html

29. Supervolcano: a mega colossal volcano, that erupts at least 1,000km3 of material. Caldera: the depression of the supervolcano marking the collapsed magma chamber. Fissures: extended opening along a line of weakness that allow magma to escape. Geothermal: water that is heated beneath the ground, which comes to the surface in a variety of ways. Geyser: a geothermal feature in which water erupts into the air under pressure. Hot spot: a section of the earth’s crust where plumes of magma rise weakening the crust. These are away from the plate boundaries. http://www.bbc.co.uk/schools/gcsebitesize/geography/natural_hazards/volcanoes_rev4.shtml

30. When a supervolcano erupts there will be global consequences • There are only a few supervolcanoes and an eruption has not happened for many years e.g. the last one was Lake Tobago supervolcano 74000 years ago. When there is an eruption it is predicted an enormous area will be affected: • A supervolcanic eruption will throw out thousands of cubic kilometres of rock, ash and lava (much more than normal volcanoes) • A thick cloud of super-heated gas and ash will flow at high speed from the volcano, killing, burning and burying everything it touches. Everything within tens of miles will be destroyed. • Ash will shoot kilometres into the air and block out almost all daylight over the whole continents. This can trigger mini ice ages as less heat energy from the sun gets to the Earth. • The ash will also settle over hundreds of square kilometres, burying fields and buildings (ash from normal volcanoes covers a couple of square kilometres.

31. Describe the likely worldwide effects of a supervolcano eruption (6 marks) • Yellowstone Case study: • In the immediate area after the eruptions many deaths are predicted totalling 87000. One in three people will be killed within 1000km of an eruption. • A large ash cloud rising 40-50km into the atmosphere • Destruction of 10000 square km of land • Ash 15cm thick covering building within 10000km causing them to collapse • Flights suspended • Live stock dies as it chokes in hot ash and farmland affected • Planes grounded and road transport difficult • The UK would see • the arrival of ash 5 days after the eruption. This circles the earth changing the climate. • temperatures would fall between 12 and 15 degrees- difficult to grow food • Parts of northern Europe and America and Asia would see constant snow cover for 3 years • Crops would fail, monsoon rains would fail and 40% of the population could face starvation

32. Millions of people live in places where volcanic eruptions can happen putting lives and risk and so we must try to predict eruptions to minimise the damage. Effective monitoring and prediction allows authorities to warn people living nearby to evacuate the area reducing the loss of human life. Mapping paths of old lava flows and mudflows can show areas of risk Electronic tiltmeters measure very small changes in the profile of the mountain. Engineering- minor lava flows can be diverted by bulldozing walls to turn the flow away from villages. In Iceland seawater is sprayed on lava flows to solidify them. Prediction of volcanic eruptions • A number if indicators help warn people of the impending eruption: • the frequency of earth tremors • gravity measurements of the movement of magma inside the volcano/ bulging around the crater • the build up of magma causing the ground temperature to rise • emissions of steam and gases such as sulphur dioxide rise Satellites are used to monitor infra-red radiation and changes in heat activity.

33. http://www.bbc.co.uk/schools/gcsebitesize/geography/natural_hazards/managing_hazards_video.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/geography/natural_hazards/managing_hazards_video.shtml