How do physical processes affect the magnitude and type of volcanic eruption? 1.Volcanoes in the world range from gentle fissure eruptions ( e.g. Heimaey, Iceland 1973) to explosive composite cone eruptions( e.g.Mt Etna , Italy 2002)Supervolcanoes also exist, such as Yellowstone National Park, USA . https://www.youtube.com/watch?v=ghl33n26d44

2.This range of volcano types reflects the amount of energy released during an eruption (See future lesson notes on this..) (e.g The supervolcano last erupted 2.1 million years ago but was 500 times greater than the Mount Pinatubo eruption of 1991)Despite the very long time period between eruptions if this were to happen again it would undoubtedly have a significant impact on the world….)

3.The shape of volcanoes is mainly related to the type of lava ejected of which there are three main types: basaltic, andesitic and rhyolitic

VOLCANIC MATERIALS: 3 TYPES OF LAVA ( see samples) https://www.youtube.com/watch?v=PRD4YZx3g2k Extrusive vulcanicity involves three different forms of lava: 1. Basaltic lava: Low in silica, more runny/fluid, allows more bubbles to expand on their way up to the surface so preventing sudden explosions. Therefore low gas content and gentle volcanoes.Typical of HOT SPOT activity such as Mauna Loa, Hawaii as well as developed volcanoes at rift systems in E.Africa and at constructive plate boundaries such as Iceland. This is the HOTTEST lava type(1000-1200 degrees C) . Formed by melting of mantle minerals mostly from upper zone but some from core/ mantle boundary.

2. Andesitic lava: Not as hot as Basaltic (800 to 1000 degrees C) Intermediate silica(60%) very viscous (which means flow is slow)often solidifying before reaching the surface and trapping gases(3/4% content) leading to a violent eruption on the surface. Typically found at destructive plate boundaries as a result of the subducted oceanic plate which melts and mixes with sea water, lithospheric mantle and continental rocks to form composite cone volcanoes such as Montserrat, Soufriere Hills, Caribbean or the Andes mountain chain, Peru, S.USA.

3. Rhyolitic lava: The coolest of all lava types(650-800 degrees C) Very high in silica (70%) extremely viscous ( N.B high viscosity traps gases- gas content is higher 4-6%). Formed from the melting of lithospheric mantle and slabs of previously subducted plate. Very violent , cataclysmic eruptions such as those of supervolcanoes (Yellowstone National Park USA) and / or found at destructive and collision margins.

Revisit today’s lesson objectives To describe and explain the global distribution of volcanic eruptions To be able to explain the causes of volcanic eruptions To be able to recognise which physical processes impact on the magnitude and type of volcanic eruption

‘ Volcanic activity at constructive and destructive plate boundaries’ PLENARY 1.Read through card sort statements and arrange in correct places on summary sheet: ‘ Volcanic activity at constructive and destructive plate boundaries’

H/W In what ways does volcanic activity vary in relation to the type of plate margin along which it flows? ( 8 marks)