Tsunamis

1. Tsunamis • What is a tsunami? • It is a giant wave or series of large waves in the ocean created by major shallow-water earthquakes and/or submarine landslides.

2. 26 December, 2004 • The worst tsunami disaster in living history was caused by an earthquake in the Indian Ocean off the island of Sumatra measuring 9.3 on the Richter Scale.

3. More than 300 000 people (many of them European holiday makers) were killed in eight Asiatic countries (in particular Indonesia/Sumatra, Sri Lanka, India, Thailand, Myanmar, Maldives, Malaysia and Bangladesh). The tidal wave even reached coastlines several thousand kilometres away, like East and Southeast Africa. There were also casualties in Somalia, Tanzania, Kenya, Madagascar and the Seychelles.

4. Activities page 97 Tsunami!

5. Activity 1 • It’s caused by an earthquake in the ocean floor (which is caused by plate movements), or giant landslide.

6. Activity 2 • Many countries border the Indian Ocean. The waves travelled across the ocean in all directions, and reached over a dozen of them. • Some countries were further from the epicentre than others, so it took longer for the waves to reach them. • The epicentre was very close to Indonesia. Somalia was thousands of kilometres away. The waves lost energy as they travelled, so they did less damage in Somalia. • The waves may be only one metre high out at sea, and in many ocean –going boats you would not notice this. The waves slow down and grow taller in the shallower water at the coast. • The Philippines were sheltered from the tsunami by Thailand and Indonesia.

7. Activity 3 • Earthquakes shake buildings and other structures, and people are killed when these collapse. • Tsunami waves rush onto the land with great force, and can wash away buildings, but also drown people far from buildings, and wash away crops, farm animals, and other forms of livelihood. • There are some things you can do to protect yourself during an earthquake. There is little you can do to protect yourself from an approaching tsunami if you are in its path.

8. Activity 5 • The buoys give out signals to satellites and these can transmit them very rapidly to places along vulnerable coastlines, giving people a chance to move away from the coast. • (The buoys collect data from pressure sensors on the ocean floor, which can detect tiny changes in wave pressure.)

10. Journey from the magma chamber • Today there are about 500 active volcanoes which are mainly located along plate boundaries. KEY WORDS: • Volcanoes are active when they have erupted within living memory. They are dormant when they have erupted within recorded history. They are extinct when they will never erupt again.

11. Volcanoes are formed when magma – molten rock still within the Earth- escapes to the surface through an opening or vent. • If the vent is blocked by cold, solid lava, pressure builds up and the following eruption can be explosive.

12. Cross-section of a volcano CRATER SUBSIDIARY CONE LAVA FLOW LAYERS OF ASH AND LAVA BRANCH PIPE VENT Draw and label a cross-section of a volcano MAGMA CHAMBER

13. SUBSIDIARY CONE CRATER

14. Volcanoes are formed when magma – molten rock still within the Earth- escapes to the surface through an opening or vent. • When magma reaches the surface it is called lava. • An eruption may be explosive if the vent is blocked by cold lava. Instead of lava, ash and volcanic bombs blow from the crater over a wide area.

15. Igneous rock • Igneous rocks are formed from the solidification of molten rock material (when melted rock hardens). • The most common extrusive igneous rock is basalt. • Other types can be pumice, obsidian, or rhyolite.

16. Basalt • Obsidian • Rhyolite

17. Pumice • Pumice is a light-colored, extremely porous igneous rock that forms during explosive volcanic eruptions.

18. PYROCLASTIC FLOWS However, the most dangerous impact of explosive eruptions is pyroclastic flows. Pyroclastic flows are made of hot gas and rocks moving at 200kmph with temperatures around 400ºc.

19. Ash and steam

20. Lahar: rapidly moving river of ash and water which can bury properties Vegetation and crops When pyroclastic flow gets mixed with water you get a river of mud called mudflow

21. The large boulders near the house are about 2 m in diameter. They are volcanic bombs.

22. Pyroclastic flow: hot gas and rocks moving at 200kmph with temperatures around 400ºc.

24. On the Caribbean Island of Martinique in 1902 a pyroclastic flow at a temperature of 700°C killed all but two of the 29 000 inhabitants of the port of St Pierre. Guess how two inhabitants managed to survive when the flow was hot enough to melt glass and metal.

25. Location of Montserrat

26. RADAR IMAGE OF MONTSERRAT

27. In July 1995 the Soufriere Hills volcano erupted for the first time in 350 years. Ash and steam

28. Pyroclastic flow: hot gas and rocks moving at 200kmph with temperatures around 400ºc.

30. Vegetation, land and homes covered in ash

32. The large boulders (volcanic bombs) near the house are about 2 m in diameter. The pyroclastic flow occurred on June 25, 1997.

33. Lahar: rapidly moving river of ash and water which buried properties Vegetation and crops

34. June 2004 Plymouth is gradually being buried by lahars

35. ACTIVITY 2: a volcano CLOUD OF ASH SECONDARY VENT CRATER DUST VOLCANIC BOMBS HOT GAS LAVA FLOW VENT MAGMA CHAMBER

36. Activity 1 page 99 • Magma is melted rock BELOW ground. The melted rock shown above ground in A and B is called lava! • Activity 3 • It looks as Plymouth was close to the volcano, and has been destroyed by eruptions. Naturally, as eruptions continued people would move away, since they could be killed. (The area is likely to remain abandoned for as long as the volcano remains active.) • Ash, dust, bits of rock, and hot gas; the gas is likely to be a mixture of steam, carbon dioxide, sulphur dioxide and other gases- and smelly.

37. Activity 4 page 99 • There is no definitive ‘correct’ order since it depends on the nature and intensity of an individual eruption, and the area affected. • Generally though, a pyroclastic flow will do more harm than a lava flow. • A POSSIBLE ORDER: • PYROCLASTIC FLOW: very fast, scorches, burns and smothers everything in its path. • ASH: can suffocate people and animals; destroys crops; causes buildings to collapse • VOLCANIC GASES: cause acid rain, can kill people, animals and plants • PLUMES OF DUST: can block out the sun, lowering temperatures around the world; can cause planes to crush • LAVA FLOW: destroys crops; can bury and burn towns and villages (but you can walk out of its way)

38. Types of volcanoes

39. Shield volcano • A shield volcano is a volcano with shallow-sloping sides. • Shield volcanoes normally form from fluid lava flows(BASALTIC LAVA) that can travel long distances across slight inclines, resulting in their relatively flat, broad profile. • In contrast, steeply sloped composite volcanoes (stratovolcanoes) bettermatch the popular stereotype of a volcano. • Some of the largest volcanoes on Earth are shield volcanoes.

40. Belknap Shield Volcano Oregon

41. Mt Takahe (Antarctica) is a large shield volcano which rises to over 11,000 feet or 3,460m. The last eruption occurred in 5550 BC.

42. Mauna Loa Shield, Hawaii

43. Composite volcano (Stratovolcano) • A composite volcano, sometimes called astratovolcano, is a tall, conical volcano with many layers (strata) of hardened lava, tephra, and volcanic ash. • Composite volcanoes are characterized by a steep profile and periodic, explosive eruptions. The lava (ANDESITIC ACID LAVA) that flows from these volcanoes tends to be thicker; it cools and hardens before spreading far. • Stratovolcanoes are also called composite volcanoes because of their composite layered structure built up from sequential outpourings of eruptive materials. • They are among the most common types of volcanoes, in contrast to the less common shield volcanoes.

44. Mount Fuji, an active composite volcano in Japan that last erupted in 1707–08.

45. Tavurvur, an active composite volcano near Rabaul in Papua New Guinea

46. Nevado Ojos del Salado ("water source of the salty river"). A massive composite volcano in the Andes on the Argentina-Chile border and the highest volcano in the world at 6,887 metres.

47. What type of volcanoes you expect to find in Chile? Why? • Composite volcanoes because Chile is close to a destructive margin. • What type of volcanoes you expect to find in Iceland? Why? • Shield volcanoes because Iceland is close to a constructive margin.

48. Describe and EXPLAIN the characteristic features of a SHIELD volcano. • A shield volcano is a volcano with shallow-sloping sides.It has gentle slopes. Shield volcanoes normally form from fluid lava flows(BASALTIC LAVA) that is hot and runny can travel long distances across slight inclines, resulting in their relatively flat, broad profile. These volcanoes are the largest (in diameter) on Earth.

49. Name three volcanic hazards 1- lava flow 2- tephra (ash) 3- pyroclastic flow 4- lahar (flow of ash and water)/mudflow 5- acid rain 6- dust

50. Which volcanic hazard is the most dangerous? • There is no definitive ‘most dangerous’ hazard because all can cause damage and loss of life. • Generally though, a pyroclastic flow (and a lahar???) will do more harm than others because it is faster and potentially more hazardous than lava or ash.