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Introducing Volcanoes

Introducing Volcanoes. With a bit of revision first. Structure of the Earth. The Earth is made up of 3 main layers: Core Mantle Crust. Mantle. Outer core. Inner core. Crust. Plate Tectonics. The Earth’s crust is divided into 12 major plates which are moved in various directions.

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Introducing Volcanoes

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  1. Introducing Volcanoes With a bit of revision first

  2. Structure of the Earth • The Earth is made up of 3 main layers: • Core • Mantle • Crust Mantle Outer core Inner core Crust

  3. Plate Tectonics • The Earth’s crust is divided into 12 major plates which are moved in various directions. • This plate motion causes them to collide, pull apart, or scrape against each other. • Each type of interaction causes a characteristic set of Earth structures or “tectonic” features. • The word, tectonic, refers to the *deformation of the crust as a consequence of plate interaction. • * deform = change shape

  4. World Plates

  5. Plate Movement • “Plates” of crust are moved around by the underlying hot mantle convection cells

  6. Three types of plate movements What happens at the margins of plates moving in this way?

  7. Where do earthquakes form? Figure showing the tectonic setting of earthquakes

  8. Just to remind you – here are the plates and …

  9. … and this is where the earthquakes occur

  10. Earthquakes • Earthquakes occur mainly on plate boundaries that are moving towards, past or away from each other • Over many years pressure builds up until eventually the rocks snap along a weak area called the FAULT LINE • The point of origin of an earthquake is the FOCUS – this is the point where it starts from • The place at the surface directly above the focus is called the EPICENTRE What sort of margin is this?

  11. The stored energy is released, travelling outwards in SEISMIC WAVES Seismic Waves are strongest at the epicentre of an earthquake – this is where the most damage is caused Seismic Waves spread out from the focus like ripples *AS SEISMIC WAVES TRAVEL OUTWARDS THEY LOSE ENERGY* The closer to the surface the focus of the earthquake is and the softer the rocks, the higher the magnitude of the seismic waves and the greater the damage

  12. The magnitude of an earthquake is measured on the Richter Scale • An earthquake’s magnitude (the strength) is measured using a seismograph. • Each subsequent level is x10 more powerful than the previous on was. • The scale is continuous (has no end) although nothing above 9.2 has not been recorded on land.

  13. Measuring Earthquakes – one way

  14. But the only problem with Richter is … • That it tells you about the strength of the earthquake at focus/epicentre and so each earthquake only has 1 value. • But obviously, this tells you nothing about what it is like further away – is there any damage? How great is the damage? • So there is another measure of earthquakes, which when you are looking them up you may come across. • It is called the Modified Mercalli Scale - it is often measured using Roman Numerals I, II, III, IV etc • Go to the animation where you can get an appreciation of what an earthquake may feel like as variuous points on the scale • http://newigcsenotes.wikispaces.com/3+Hazardous+environments

  15. An example • On September 29 there was an earthquake under the sea, south of Samoa and American Samoa had a Richter scale of 8.0 (or 8.3 depends who you read). • But the Mercalli scales for these were Samoa felt (V) and (IV) at American Samoa. • But it was the tsunami that did the damage. At least 149 people killed in Samoa, 34 people in American Samoa and nine people killed and four injured on Niuatoputapu, Tonga. Widespread damage to infrastructure at Pago Pago and Samoa.

  16. What is an earthquake like?

  17. There are 2 types of waves in an earthquake • Body waves and surface waves. • Body waves travel outward in all directions, including downward, from the quake's focus -- that is, the particular spot where the fault first began to rupture. • Surface waves, by contrast, are confined to the upper few hundred miles of the crust. • They travel parallel to the surface, like ripples on the surface of a pond out from the focus. They are also slower than body waves.

  18. Following an earthquake … • ..the body waves (P-wave) strike first and are the fastest kind People often report a sound like a train just before they feel a quake, which is the P-wave moving as an acoustic wave in the air. • Then the secondary, or S-waves, arrive. A person in a building perceives the arrival of S-waves as a sudden powerful jolt, as if a giant has pounded his fist down on the roof. • Finally, the surface waves strike. In very strong earthquakes, the up-and-down and back-and-forth motions caused by surface waves can make the ground appear to roll like the surface of the ocean, and can literally topple buildings over.

  19. In Washington State 2001

  20. In Washington State 2001

  21. Now for Volcanoes

  22. Just to remind you – here are the plates and … Where are the places the volcanoes occur most commonly? Why is that?

  23. Ring of Fire

  24. The main effects of a volcanic eruption include: • Often earthquakes occurring near a volcano can be one of the first warnings of things to come • Larva: it can be thick, viscous (sticky) lava or much more runny. • The thick lava moves relatively slowly and hardens quickly to form new rock – and so forms a cone shape a cone shape. Eruptions tend to be violent. • Eruptions that give out the thin, runny lava tend to be frequent but relatively gentle and come from a shield volcano

  25. The main effects of a volcanic eruption include: • Pyroclastic flow: some vlocanoes do not give out lava alone but a mixture of hot steam, ash, rock and dust. • A pyroclastic flow can roll down the sides of a volcano at very high speeds and with temperatures of over 400° C.

  26. Direct measurements of pyroclastic flows are extremely dangerous!!! • A truck carrying volcanologists and a film crew attempting to out run a pyroclastic flow …. • the pyroclastic flow was traveling at about 25-30 meters per second….. • they made it…. • just!

  27. The main effects of a volcanic eruption include: • Ash clouds may affect more than the immediate area. They consist of water vapour, sulphur gas as well as small rock fragments and tiny pieces of glass. • Many of these will return to earth and add a layer of dust to a wide area. • However, the gases may be carried a long way by the wind once they have reached high enough into the atmosphere. This may be carried all around the world ad has in the past had a lasting impact on the climate, lowering the temperature for a year or more. E.g. Krakatoa in 1883 is the largest volcano eruption in recorded history for which we have data. • Average global temperatures fell by as much as 1.2 degrees Celsius in the year following the eruption. Weather patterns continued to be chaotic for years and temperatures did not return to normal until 1888.

  28. Finally Lehars • These can occur at the same time as a volcanic eruption but may also occur over succeeding years. • Lahars form when water from intense rainfall, melting snow and ice, or the sudden failure of a natural dam, mixes with loose volcanic material, creating mudflows that can be particularly dangerous and destructive. • Although lahars contain a lot of volcanic ash and rock fragments–making them dense and viscous like wet concrete–they actually flow faster than clear-water streams. • These mudflows can rush down the flanks of a volcano at speeds as great as 65 kilometres per hour and can travel more than 80 kilometres. Lahars that contain the most debris move the fastest and are the most destructive.

  29. We can measure storms and measure earthquakes, why not volcanoes? • Measuring movement of plates and the kind of damage done is fairly straight forward. Measure storms is simple – it is the wind speed that tells the story. • But measuring volcanoes is a whole lot more complicated. What do you measure? The clouds of dust, the speed of the lava, how much lahar there is? Different volcanoes behave in their own special way – it is not possible to have universal measures that apply to all circumstances. • However, local methods of issuing warning are being developed – some use a colour code system, some numbers – most use 1 as low level and 4 or 5 as high levels of danger – but then again some use a reverse order with 1 being the highest level of alert.

  30. This is scale used in Indonesia This is scale used in Alaska This is scale used in Columbia in South America

  31. Why am I telling you this? • As you might suppose you might need it in your homework. • I want you to find out about as least one recent earthquake and one recent volcanic eruption – no specific time limits but there have been a number of quite serious earthquakes in the last 6 months but few volcanic eruptions, so I would suggest you might need to go further back for volcanoes perhaps. • I want to know where it is with a map if possible (and most sites about disasters do have maps), what happened and what was the impact of it on the place – short term and long term. And only if you happen to come across it, how they coped/are coping – who is helping etc. [DO NOT SEARCH FOR THIS LAST PART]

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