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Volcanoes These icons indicate that teacher’s notes or useful web addresses are available in the Notes Page. This icon indicates the slide contains activities.

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Presentation on theme: "Volcanoes These icons indicate that teacher’s notes or useful web addresses are available in the Notes Page. This icon indicates the slide contains activities."— Presentation transcript:

1 Volcanoes These icons indicate that teacher’s notes or useful web addresses are available in the Notes Page. This icon indicates the slide contains activities created in Flash. These activities are not editable. For more detailed instructions, see the Getting Started presentation. 1 of 35 © Boardworks Ltd 2005

2 Learning objectives What is a volcano? Why do volcanoes occur?
Where are volcanoes found? What happened in the 1980 Mount St Helens eruption? Can volcanic eruptions be predicted? Why do people live in volcanic areas? Learning objectives

3 What is a volcano? A volcano is an opening or vent in the earth’s surface through which molten material erupts and solidifies as lava. Volcanic vent

4 Label this cross section of a volcano
Volcanic bombs, ash, lava, gases Magma chamber Parasitic cone Crater Main vent

5 Cross section of a volcano
Volcanic bombs, ash and gases Crater Parasitic cone Main vent Magma chamber

6 Cross section of a volcano

7 Volcanic emissions

8 Volcanic emissions

9 Do all volcanoes erupt? Active volcano – liable to erupt e.g. Mt Etna.
Dormant (sleeping) volcano – a volcano which has not erupted for many years. For example, Mt Pinatubo erupted in 1991 after 500 years of dormancy. Extinct volcano – a volcano which has not erupted for many thousands or millions of years e.g. Edinburgh. However, it is often very difficult to tell whether a volcano will erupt again…El Chichon, Mexico erupted in 1982 after being dormant for approximately 1200 years!

10 Learning objectives What is a volcano? Why do volcanoes occur?
Where are volcanoes found? What happened in the 1980 Mount St Helens eruption? Can volcanic eruptions be predicted? Why do people live in volcanic areas? Learning objectives

11 Why do they happen? A destructive plate boundary is found where a continental plate meets an oceanic plate. The oceanic plate descends under the continental plate because it is denser. As the plate descends it starts to melt due to the friction caused by the movement between the plates. This melted plate is now hot, liquid rock (magma). The magma rises through the gaps in the continental plate. If it reaches the surface, the liquid rock forms a volcano.

12 Destructive plate boundary

13 Why do they happen? At a constructive plate boundary, two plates move apart. As the two plates move apart, magma rises up to fill the gap. This causes volcanoes. However, since the magma can escape easily at the surface, the volcano does not erupt with much force.

14 Constructive plate boundary

15 Volcano shapes Why do volcanoes have different shapes?

16 Volcano shapes

17 Volcanic activity at plate margins

18 Learning objectives What is a volcano? Why do volcanoes occur?
Where are volcanoes found? What happened in the 1980 Mount St Helens eruption? Can volcanic eruptions be predicted? Why do people live in volcanic areas? Learning objectives

19 Where are volcanoes found?
Around which plate do we find most volcanoes?

20 Hawaii The Hawaiian islands are a chain of volcanoes in the Pacific Ocean. Look at their location on the map below. Why is this an unusual place for them to be located?

21 Hot spot volcanoes This ‘conveyor belt’ animation is a simplified version of the formation of hot spot volcanoes/ chains of islands. Internet Links – US Geological Survey Hawaiian volcanoes While all care is taken to ensure web links contain useful information, Boardworks does not take responsibility for the content or accuracy of external web sites. In the animation above, why are the volcanoes to the left of the ‘hot spot’ extinct?

22 Learning objectives What is a volcano? Why do volcanoes occur?
Where are volcanoes found? What happened in the 1980 Mount St Helens eruption? Can volcanic eruptions be predicted? Why do people live in volcanic areas? Learning objectives

23 Mt St Helens eruption (May 1980)
Mt St Helens is located on the ‘Ring of Fire’. While all care is taken to ensure web links contain useful information, Boardworks does not take responsibility for the content or accuracy of external web sites. Internet Links

24 Mt St Helens – causes of the eruption
Mt St Helens is located on a destructive plate boundary where a continental plate (North American) meets an oceanic plate (Juan de Fuca). Juan de Fuca plate North American plate Which plate is denser? Describe what happens when the oceanic plate descends under the continental plate.

25 Mt St Helens – the eruption
Animation showing the Mt St Helen’s eruption with text.

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29 Mount St. Helens woke up on March 20, 1980, with a Richter magnitude 5
Mount St. Helens woke up on March 20, 1980, with a Richter magnitude 5.1 earthquake. Steam venting started on March 27. By the end of April, the north side of the mountain started to bulge. With little warning, a Richter magnitude 5.1 earthquake triggered a massive collapse of the north face of the mountain on May 18. This was the largest known debris avalanche in recorded history. The magma inside of St. Helens burst forth into a large-scale pyroclastic flow which flattened vegetation and buildings in an area of over 230 square miles (600 km²). This eruption was a 5 on the Volcanic Explosivity Index scale. For more than nine hours, a vigorous plume of ash erupted, eventually reaching 12 to 15 miles (20 to 25 km) above sea level. The plume moved eastward at an average speed of 60 miles per hour (95 km/h), with ash reaching Idaho by noon. The collapse of the northern flank of St. Helens mixed with ice, snow, and water to create lahars (volcanic mudflows). The lahars flowed many miles down the Toutle and Cowlitz Rivers, destroying bridges and lumber camps. A total of 3.9 million cubic yards (3.0 million cubic meters) of material was transported by the lahars. By around 5:30 PM on May 18 the vertical ash column declined in stature but less severe outbursts continued through the night and the following several days. In all, St. Helens released an amount of energy equivalent to 27,000 Hiroshima-sized atomic bombs and ejected more than a cubic kilometre of material. The removal of the north side of the mountain reduced St. Helens' height by about 1300 feet (400 m) and left a 1 to 2 mile (1.6 to 3.2 km) wide and 0.5 mile (800 m) deep crater with its north end open in a huge breach. Fifty-seven people were killed along with 1500 elk, 5000 deer, and an estimated 11 million fish. In addition, 200 homes, 47 bridges, and 185 miles (300 km) of highway were destroyed.

30 VEI Description Plume Height Volume Classification How often Example non-explosive < 100 m 1000s m3 Hawaiian daily Kilauea 1 gentle m 10,000s m3 Haw/Strombolian Stromboli 2 explosive 1-5 km 1,000,000s m3 Strom/Vulcanian weekly Galeras, 1992 3 severe 3-15 km 10,000,000s m3 Vulcanian yearly Ruiz, 1985 4 cataclysmic 10-25 km 100,000,000s m3 Vulc/Plinian 10's of years Galunggung, 1982 5 paroxysmal >25 km 1 km3 Plinian 100's of years St. Helens, 1981 6 colossal 10s km3 Plin/Ultra-Plinian Krakatau, 1883 7 super-colossal 100s km3 Ultra-Plinian 1000's of years Tambora, 1815 8 mega-colossal 1,000s km3 10,000's of years Yellowstone, 2 Ma

31 Mt St Helens – consequences of the eruption
10km

32 Mt St Helens – consequences of the eruption
AFTER BEFORE

33 What damage did the eruption cause?
Other impacts of the 1980 St Helens eruption (students may be encouraged to explore how short-term impacts can have long-term consequences) 60 people die from the eruption. Two million birds, animals and fish are killed. Damage to crops=$175million The post office and Lone Fir Motel shut down in Cougar. The US army takes 18 months to dig out the debris from the River Toutle.

34 Mt St Helens – consequences of the eruption
Why do you think animals such as the vole and gopher survived the blast? How did their survival benefit the area? What benefits might the volcanic activity have brought to Mt St Helens?

35 Learning objectives What is a volcano? Why do volcanoes occur?
Where are volcanoes found? What happened in the 1980 Mount St Helens eruption? Can volcanic eruptions be predicted? Why do people live in volcanic areas? Learning objectives

36 Predicting eruptions

37 The problem of prediction
Volcanologists (people who study volcanoes) are skilled at predicting the likelihood of an eruption. However, it's very difficult to pinpoint exactly when an eruption will happen. Often, moving magma doesn't result in an eruption, but instead cools below the surface. Monitoring potential eruptions is expensive. With many volcanoes erupting only every few hundred years, it's not possible to monitor every site.

38 Precautions during an eruption

39 Learning objectives What is a volcano? Why do volcanoes occur?
Where are volcanoes found? What happened in the 1980 Mount St Helens eruption? Can volcanic eruptions be predicted? Why do people live in volcanic areas? Learning objectives

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

41 Internet links Volcano World - a fun and informative web site Virtual field visits The Michigan Technological University Volcanoes Page Global Volcanism Program Fallout: Eye on the Volcano Savage earth While all care is taken to ensure web links contain useful information, Boardworks does not take responsibility for the content or accuracy of external web sites.


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