Hotspot volcanism

In the previous videos you have already seen that shield volcanoes appear at divergent zones and stratovolcanoes appear at convergent zones. Yet there are also volcanoes that do not originate at a plate boundary. These volcanoes were created at hotspots.

Sometimes a mantle plume arises in the mantle. This is a local warm magma stream that is directed upwards. This magma plume burns through the crust and forms a shield volcano in the middle of a plate. A hotspot is therefore easily recognized by the occurrence of volcanism, while there is no plate boundary nearby.
Because it concerns shield volcanoes, the eruptions are usually effussive. The oceanic crust is much thinner than the continental crust, so that a mantle plume burns through the crust faster. That is why there are relatively few hotspots on the continents.

A mantle plume usually stays at the same location. But you have already seen in previous videos that the plates move. This often creates a group of islands.
For example, Hawaii came into existence because a mantle plume burned through the Pacific plate. Once outside the earth's crust, the lava solidified. Many eruptions later, the volcano rose above sea level; the first island came into being. Because the plate moved further north-west, the supply of magma stopped. The volcano could not continue to grow. Due to erosion the height of the volcano decreased and the volcano became smaller.
Meanwhile, the mantle plume also formed a volcano on the next piece of plate. Here too, after a number of eruptions, the volcano rose above sea level and a new island had emerged.

In this way a series of islands emerged. The oldest island is often the smallest, because this island has already been eroded the most.

Hawaii is a good example, but more island groups have emerged this way. Other examples are the Azores, the Cape Verde Islands, the Canary Islands, the Galapagos Islands and Yellowstone.

Scientists do not yet agree where the mantle plume comes from. Some scientists think that the mantle plume comes form a very deep part of the mantle, while others suspect that the magma starts to rise just below the crust.

So you have learned that island groups in the middle of an ocean crust are created by a hotspot. The mantal plume or hot spot stays in place, while the oceanic plate moves. This can result in long rows of islands. The oldest island is usually the smallest and the furthest away from the hotspot.