1. 1.1: W HERE V OLCANOES A RE L OCATED 1. Describe how the locations of volcanoes are related to plate tectonics. 2. Suggest why volcanoes are found at convergent and divergent plate boundaries. 3. Describe how intraplate volcanoes form.

2. Volcanic activity takes place primarily at convergent boundaries where subduction occurs. H OW AND W HERE V OLCANOES F ORM Oceanic lithosphere Continental lithosphere Asthenosphere 1. Water in the subducted rock is released into the asthenosphere. 2. The water lowers the melting temperatures of materials in the asthenosphere, leading to magma formation. 3. The magma is less dense than its surroundings, so it rises. 4. Some of the magma reaches Earth’s surface, and volcanoes form on the overriding continental plate.

3. H OW AND W HERE V OLCANOES F ORM Examples: Cascades in North America Aleutian Islands Drone video in Iceland

4. H OW AND W HERE V OLCANOES F ORM Divergent boundaries Where a hotspot is located along a ridge. Examples: Iceland, East African Rift Valley

5. H OW AND W HERE V OLCANOES F ORM 1. Hot mantle rock rises as plates move apart. 2. This releases pressure, which lowers the melting temperature. 3. Lava erupts through fissures.

6. The Hawaiian Islands formed over a hot spot. Magma and volcanoes also form at hotspots. Direction of Plate Movement Kauai Oahu Molokai Lanai Maui Hawaii How and Where Volcanoes Form

7. Examples: Hawaiian Islands, Society Islands

8. V OLCANIC S ETTINGS

9. Major Volcanoes Around the World

10. W HERE THE MAJORITY OF VOLCANIC ACTIVITY ON THE E ARTH OCCURS.

11. 1.2: V OLCANIC E RUPTIONS 1. Explain how magma composition affects the type of eruption. 2. Compare the types of volcanic eruptions. 3. Distinguish between different types of lava and the rocks they form. 4. Describe a method for predicting volcanic eruptions.

12. E RUPTIONS ARE U NIQUE Dependent on the Chemical Composition of Magma. This determines: Eruption style Type of cone that forms Composition of rocks found there Viscosity- a liquids resistance to flow LOW HIGH

13. T YPES OF M AGMA Mafic Low silica content Dark colored Low Viscosity Felsic High silica content Light colored High Viscosity

14. T YPES OF E RUPTIONS Explosive Due to Felsic magma Example: Mt Redoubt in Alaska, 1989 Effusive Due to Mafic magma

15. L AVA FROM E FFUSIVE E RUPTIONS Pahoehoe - smooth, ropy lava produced when the lava flows steadily because it is less viscous. Pahoehoe Lava flowing (Pa-Hoy-Hoy)

16. L AVA FROM E FFUSIVE E RUPTIONS A’a A’a – rough and jagged lava that is produced when viscous lava hardens quickly. Can be one large spiky mass Or individual sharp rocks. (Ah-Ah)

17. L AVA FROM E FFUSIVE E RUPTIONS Pillow Lava- Pillow Lava- formed from mafic lava that erupts underwater, it cools instantly forming pillow-shaped rocks.

18. E RUPTION M ATERIAL Tephra Magma, rock and ash ejected from a volcano Pyroclastic Flow Scorching hot (1000˚C) tephra, ash, and gas Fast moving (450 mph) down slopes Lahar Melted snow creating a volcanic mudflow Lahars in Japan 2012

19. P REDICTING V OLCANIC E RUPTIONS History of previous volcanic activity Earthquakes Slope Deformation Gas Emissions

20. H ISTORY OF V OLCANIC A CTIVITY Looks at “How long since its last eruption and the time span between previous eruptions?” Active: Currently erupting or showing signs of erupting soon. Dormant: No current activity, but has erupted recently Extinct: No activity for some time; will probably not erupt again. Bardarbunga in Iceland Hohentweiel in Germany Mt Vesuvius in Italy

21. P REDICTING V OLCANIC E RUPTIONS Earthquakes: Moving magma shakes the ground Number and size may increase before an eruption Slope Deformation: Magma and gas push slope upward Tiltmeters- measures the angle of the slope Ground swelling may increase rock falls and landslides Gas Emissions: The amounts of gases and their ratios are measured at vents or from a distance using satellites. Satellites can also be used to measure temperature and deformation.

22. I MPROVING A CCURACY IN P REDICTIONS Uncertainty about eruptions. A false evacuation may make people less likely to evacuate in the future. Cost of disrupting business is great, especially if it ends up being a false alarm.