Volcanoes Key Question: What are the causes of volcanoes?

Key Colour code the top of your sheet to match the key = Location / Plates = Processes = Volcano Type, Lava Type and Explosiveness = Explanation of how processes causes melting

Constructive Plate Margins E.g. Iceland, Mid Atlantic Ridge N. American Plate Eurasian Plate Explanation: Plates pull apart (extends) under tension due to sea floor spreading Lithosphere thins and asthenosphere rises to fill gap Partial melting of peridotite generates basalt magma Red volcanoes form, effusive basalt is erupted

E.g. Indonesia Destructive Plate Margins: Oceanic-oceanic Explanation: Pacific Plate Indonesian Plate Oldest coldest plate subducts Oceanic subducting plate drags down with it sediments on ocean floor that contain water Water is released and lowers the melting point of the asthenosphere in the mantle wedge above the subducting plate Partial melting in the mantle wedge occurs and high silica magmas are created which erupt explosively from grey volcanoes as andesite and rhyolite

E.g. The Andes (Andean Volcanoes) Destructive Plate Margins: Oceanic-continental Explanation: S. American Plate Nazca Plate The oceanic plate subducts Water held in the ocean floor sediments is also dragged down with the subduction Water is released and lowers the melting point of the asthenosphere in the mantle wedge above the subducting plate Partial melting occurs in the mantle wedge and high silica magmas are created which erupt explosively from grey volcanoes as andesite lavas

E.g. The E. African Rift (Kilimanjaro) Rift Valley: Explanation: African Plate African Plate Plates pull apart by rifting within the centre of a plate to form a rift valley. Thinning of the lithosphere due to extension causes asthenosphere to rise closer to the surface Partial melting of asthenosphere causes a range of lavas (Basalt-Rhyolite) ..and a range of volcanoes both cone and shield!

Intra-Plate Margins: E.g. Hawaii Hot Spots A ‘hot spot’ in the mantle caused by a rising plume which remains stationary The plume head partially melts the asthenosphere generating effusive basalts (aa and pahoe hoe) and shield volcanoes As the plate moves off the hotspot the volcanoes cease. Pacific Plate

1. Draw a pair of arrows to show the plate motion at this type of margin (2) 2. Name the margin? (1) 3. What type of volcanoes and lava would form here? (2) 4. Add two plate names to the diagram to suggest where this is (2) 5. Explain in your own words why volcanoes form at this margin? (4) Pay attention to SPAG.