Volcanoes at Hotspots Unlike other volcanoes, volcanoes at hotspots form away from plate boundaries on both continental and oceanic plates. Hotspots occur due to unusually hot plumes of magma rising through the mantle beneath a thin layer of oceanic plate. The magma is so hot that it begins to melt through the plate, eventually reaching the surface. The magma does not contain many volatile gases so eruptions are not violent. Instead, the lava simply flows from the vent.
Lava reaches the surface at a very high temperature (1200 °C). The basic lava is very runny and flows quickly away from the vent before cooling on the surface. Volcanoes at hotspots are very gently sloping (between 2 and 10°) and are often referred to as shield volcanoes. As a plate moves over a hotspot, a chain of volcanic islands is formed, e.g. Hawaii.
) Fig. 3.9 Hawaiian Islands were formed by hotspots
Kauai: 4.7 million years old
Oahu: 2.8 million years old
Molokai : 1.5 million years old Maui: 1.05
Direction of plate movement
ACTIVE LEARNING
Using Fig. 3.10, explain the different ways in which volcanoes can form.
