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Download 1.3: Types of Volcanoes
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1.1: WHERE VOLCANOES ARE LOCATED 1. 2. 3. Describe how the locations of volcanoes are related to plate tectonics. Suggest why volcanoes are found at convergent and divergent plate boundaries. Describe how intraplate volcanoes form. HOW AND WHERE VOLCANOES FORM Volcanic activity takes place primarily at convergent boundaries where subduction occurs. 1. Water in the subducted rock is released into the asthenosphere. 4. Some of the magma reaches Earth’s surface, and volcanoes form on the overriding continental plate. Oceanic lithosphere Asthenosphere 2. The water lowers the melting temperatures of materials in the asthenosphere, leading to magma formation. Continental lithosphere 3. The magma is less dense than its surroundings, so it rises. HOW AND WHERE VOLCANOES FORM Examples: Cascades in North America Aleutian Islands Drone video in Iceland HOW AND WHERE VOLCANOES FORM Divergent boundaries Where a hotspot is located along a ridge. Examples: Iceland, East African Rift Valley HOW AND WHERE VOLCANOES FORM 3. Lava erupts through fissures. 2. This releases pressure, which lowers the melting temperature. 1. Hot mantle rock rises as plates move apart. How and Where Volcanoes Form Magma and volcanoes also form at hotspots. Kauai Oahu Direction of Plate Movement Molokai Lanai Maui Hawaii The Hawaiian Islands formed over a hot spot. Examples: Hawaiian Islands, Society Islands VOLCANIC SETTINGS Major Volcanoes Around the World WHERE THE MAJORITY OF VOLCANIC ACTIVITY ON THE EARTH OCCURS. 1.2: VOLCANIC ERUPTIONS 1. 2. 3. 4. Explain how magma composition affects the type of eruption. Compare the types of volcanic eruptions. Distinguish between different types of lava and the rocks they form. Describe a method for predicting volcanic eruptions. ERUPTIONS ARE UNIQUE 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 TYPES OF MAGMA Mafic Low silica content Dark colored Low Viscosity Felsic High silica content Light colored High Viscosity TYPES OF ERUPTIONS Explosive Due to Felsic magma Example: Mt Redoubt in Alaska, 1989 Effusive Due to Mafic magma LAVA FROM EFFUSIVE ERUPTIONS Pahoehoe- smooth, ropy lava produced when the lava flows steadily because it is less viscous. Pahoehoe Lava flowing (Pa-Hoy-Hoy) LAVA FROM EFFUSIVE ERUPTIONS A’a – rough and jagged lava that is produced when viscous lava hardens quickly. (Ah-Ah) Can be one large spiky mass Or individual sharp rocks. LAVA FROM EFFUSIVE ERUPTIONS Pillow Lava- formed from mafic lava that erupts underwater, it cools instantly forming pillow-shaped rocks. ERUPTION MATERIAL 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 PREDICTING VOLCANIC ERUPTIONS History of previous volcanic activity Earthquakes Slope Deformation Gas Emissions HISTORY OF VOLCANIC ACTIVITY Looks at “How long since its last eruption and the time span between previous eruptions?” Bardarbunga in Iceland 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. Hohentweiel in Germany Mt Vesuvius in Italy PREDICTING VOLCANIC ERUPTIONS 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. IMPROVING ACCURACY IN PREDICTIONS 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.
