GCSE- Tectonic Landscapes: Understanding hotspots
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Watch the video on Hawaiian Islands Formation from Khan Academy
Some volcanoes do not occur on plate boundaries. These volcanoes are formed over hotspots.
- These are fixed points in the mantle that generate intense heat (in a mantle plume). Small, long lasting, exceptionally hot areas of magma exist under the Earth’s surface which in turn sustains long-lasting volcanic activity.
- At areas where the pressure is greater in the mantle, magma erupts through the crust as when the plume reaches the crust it causes the crust to dome (and crack).
- Volcanoes are created if the magma rises above the ocean surface.
- As the crustal plate moves over the stationary hotspot, new volcanoes are formed. Hotspots are associated with chains of islands. Examples are the Samoa Islands and Hawaii.
- As the plate moves the volcano will progressively become dormant and extinct and the volcano will be eroded by the sea.
Figure 1 As the crustal plate moves over the stationary hotspot, new volcanoes are formed.
Case study: The Hawaiian Islands, which are entirely of volcanic origin, have formed in the middle of the Pacific Ocean more than 3,200 km from the nearest plate boundary. The Hawaiian Islands are located over a hotspot. The magma rises through the Pacific Plate to supply the active volcanoes.
Why are volcanoes located over a hot spot progressively older and eroded?
The Hawaiian volcanoes are progressively older and increasingly eroded the further they are from the hotspot as they were once located above the stationary hot spot but were carried away as the Pacific Plate drifted to the northwest. Watch this short animation which shows how old volcanoes are eroded by wave action.
Figure 2 Volcanoes located over the Hawaiian hotspot are progressively older and increasingly eroded.