How are volcanoes formed at destructive/convergent plate boundaries? Acid lava/composite cone volcanoes: Formed at destructive plate boundaries where the oceanic crust slips beneath the continental crust in the subduction zone. As a result the crust melts in the subduction zone and magma moves upwards and out of lines of surface weaknesses as lava as a fierce volcano e.g. Mt Etna, Sicily https://www.youtube.com/watch?v=Kg_UBLFUpYQ (‘Tectonics of the planet earth’ from@5.42 secs)

Destructive – Convergent 5. Fold mountains form as sediments are crumpled up on leading edges of continental masses 1.Convection currents cool and descend causing two plates to be pulled towards each other( or by ‘slab pull theory’) Oceanic crust denser/heavier but thinner forced beneath lighter continental crust Continental Crust Oceanic Crust 4. Could lead to rising magma (molten rock) – volcanic eruption 3.Friction causes heat which melts ocean crust in to mantle – causes earthquakes in the Benioff zone 2. Crust Melts in subduction zone and creates a deep ocean trench

MT.ETNA SICILY 2002 ERUPTION

Shield volcano (basaltic lava) Types of volcano Composite Volcano (Andesitic lava) Eg Mount Etna, Sicily Steep-sided symmetrical cone shape High with narrow base Alternate layers of andesitic lava and ash Lava may cool inside vent – the next eruption is very explosive to remove the plug Subsidiary cones and vents form. Sporadic eruptions/ dormant periods Shield volcano (basaltic lava) Eg. Mauna Loa and Kilauea (Hawaiian Isl) Gentle slopes and wide base Frequent eruptions of basaltic lava Lava flows more easily, travels longer distances before cooling Usually non-violent

H/W TASK 2 Try exam question p.69