Download Tectonic landscapes- Understanding hotspots

1
GCSE- Tectonic landscapes- Understanding hotspots
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 longlasting 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: 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?
2
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.
Past questions:
Explain the formation of a volcano at a hotspot. You may use a labelled diagram(s) in your answer.
(4)
Hot spot volcanoes are associated with magma rising to the surface (in a mantle plume) (1). They are
found mid-plate (intra-plate) (1). This occurs as the material is less dense (hotter) than that around it
in the mantle (1). When the plume reaches the crust it causes the crust to dome (and crack) (1),
which allows magma a route to the surface. Over time eruptions will build up on the surface and this
may lead to the formation of a volcano above sea level. As the plate moves the volcano will
progressively become dormant and extinct and the volcano will be eroded by the sea.
Study Figure 4b. It shows hotspot volcanoes.
(i) In which direction is the plate moving? West
(ii) On which type of plate do hotspot volcanoes usually occur? Oceanic
(iii) Draw a labelled diagram to show how the chain of islands will change over time. (3)
Credit changes over time to 2 marks. Max 2 if not labelled.
Could show erosion of present day cone; build-up of present day cone due to volcanic activity;
development of a new volcanic cone (to east of present).