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Volcanic Landforms Extrusive & Intrusive Introduction to Volcanic landforms Extrusive (above the earth's surface) ● Vent eruptions ○ classic volcanoes ● Fissure Eruptions ○ mid-atlantic ridge ● Hot Spots ○ weak point in earth's crust ○ Hawaiian islands Intrusive (formed in the earth's crust ● Batholith ○ slow cooling magma in the earth's crust ● Leinster Batholith ○ Wicklow & Dublin Mts ○ Granite batholith exposed by weathering Extrusive landforms ● Vent Eruptions ○ Cone Shaped Volcanoes ○ Dome shaped volcanoes ● Fissure Eruptions ○ Mid-Atlantic Ridge ○ Antrim Plateau in Ireland ● Hot Spots ○ Hawaiian islands ○ Not near plate boundary Mount Vesuvius - Cone Shaped Volcano (Classic volcano shape) What are vent eruptions? ● Eruptions through a vent ● Occur at destructive boundaries (subduction zones) ● Volcano made of lava and ash ● Crater on top - filled with water or cooled rock Crater on Mount Vesuvius Cone Shaped & Dome Shaped Volcanoes Cone Shaped Volcanoes ● ● ● ● Made up of layers of lava and ash & cinders Lava glues with ash & cinders Steep cone shape builds up Mount Vesuvius Cone Shaped Volcano in the Philippines Dome Shaped Volcanoes ● ● Mound shaped volcano - made of slow moving lava that cannot flow far Slow moving lava due to high viscosity (very thick & high silica content) Dome Shaped Volcano - Mt St Helens (USA) Fissure Eruptions ● ● ● ● Fissure eruption are caused by crack in earth's crust Fissure can be many kms long Main example is Mid-Atlantic Ridge Fissure eruptions produce basic lava (low silica content and very runny) ● Lava can spread over 50km ● Antrim Plateau in Ireland (made of basalt & includes Giant's Causeway ● Mid-Atlantic Ridge - includes Iceland (made of basalt) Fissure Eruptions Antrim Plateau Mid-Atlantic Ridge in Iceland More on the Antrim Plateau ● Fissure Eruption ● Formed 65 million years ago due to separating plates (North American & Eurasian plate separating) ● Basalt Plateau (high flat topped land) extending over Antrim & Derry ● Basic lava (low silica & gas content) flowed onto the surface due to plate divergence ● Includes Giant's Causeway - rapid cooling of lava led to shrinking and formation of hexagonal shape Hot-Spots ● Hawaii Islands ● Caused by intense heat from the mantle ● Causes break in the crust that allow lave through ● Basic lava -very runny ● Hot spot remains in the same place ● Plate above the hot spot moves ● This causes a chain of volcanic islands to form Hawaii Hotspot - the hotspot remains stationary. As the pacific plate moves north, new volcanoes are formed. The oldest islands are now furthest from the hotspot. Intrusive Landforms ● Intrusive - formed by magma that does not reach the surface ● Main intrusive landform is a batholith ● Example: Leinster Batholith (Granite Rock) Leinster Batholith (Granite Rock) The Leinster Batholith ● ● ● ● ● ● Large area - includes Dublin & Wicklow Mts Formed 400 million years ago as magma was injected into crust Magma cooled slowly to form granite Heat from magma changed surrounding rocks into metamorphics (Quartzite & Schist) Weathering & Erosion over millions of years of the over-lying rock have exposed this granite Leinster Batholith now form the granite Wicklow & Dublin Mts Slow cooling magma in earth's crust Diagram of Batholith