Do all volcanic eruptions occur at plate boundaries

Asked Henryn recently. You can see Sensei's answer here or read The AnswerBanks extended answer here.

A. No, although the vast majority of volcanic eruptions occur near plate boundaries, there are some exceptions. The most well known example of this is the Hawaiian Islands, which are entirely of volcanic origin, and have formed more than 3,200 km from the nearest plate boundary, in the middle of the Pacific Ocean. Intraplate volcanism, volcanic activity away from plate boundaries, is commonly known as hotspots.

The hotspot theory was first hit upon by, J. Tuzo Wilson, the Canadian geophysicist, in 1963.

Q. What is a hotspot

A. Hot spots are areas of persistent volcanic activity. Unusually intense heat at the Earth's mantle causes some of it to melt, sending rising plumes of magma through the Earth's crust where they create volcanoes or hot springs.

Q. How do island volcanoes produced by hotspots form

A. The heat from the hotspot means that magma is constantly produced. The magma, which is lighter than the surrounding solid rock, rises through the mantle and crust to erupt onto the seafloor, forming an active mound, called a seamount. Over time, countless eruptions cause the seamount to grow until it finally emerges above sea level to form an island volcano.

Since the Earth's plates are moving, but the hotspots are stationary, the magma is eventually cut off and volcanic activity stops. But as one volcanoes becomes extinct another one develops over the hotspot. Over millions of years a string of volcanic islands, like the Hawaiian islands, forms.

Q. Other than Hawaii, what other hotspots exist

A. Hotspots occur all around the world, on continental and oceanic plates.

Yellowstone National Park in the USA is another famous hotspot, but one that produces geysers and hot pools rather than magma.

There are thought to be about a hundred hotspots beneath the Earth's crust that have been active at some point during the last 10 million years.

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by Lisa Cardy