LATE TECTONICS 1.5 Tectonic activity in the middle of plates – hotspots
Sometimes volcanoes are found thousands of miles from the edges of plates. They occur in areas where high temperatures in the mantle produce a rising fountain (plume) of molten rock known as a hotspot. Hotspots are extremely hot areas deep in the upper mantle (asthenosphere). A column of magma rises from the hotspot and pushes to the surface erupting through the plate above. It is thought that these fountains are stationary inside the asthenosphere and the plates move over them. As this happens magma erupts through fissures or other weaknesses in the crust, creating volcanoes. The Hawaiian Islands were formed over one such hotspot. Some hotspots stretch and split the crust causing rift valleys, e.g. the East African Rift Valley.
Oldest island – extinct volcano
New island – active volcano
Plume of magma Tectonic plate
carries islands away from the hotspot
Hotspot rising from the mantle
Fig. 24 The Hawaiian hotspot volcanoes
ACTIVITY
1. Locate the following on a map of the world: (a) The Hawaiian hotspot (b) Three types of plate boundary (c) Two named trenches