Explain the formation of a hot spot. (7marks)
Hot spots are anomalies in the pattern of volcanic activity upon plate margins. They are often in the middle of plates.
A hot spot can be described as a small area of the earth’s crust where an unusually high heat flow or plume is associated with volcanic activity. Of approximately 125 hot spots thought to have been active over the past 10 million years most are located well away from plate boundaries. It is the fact that they have posed so much trouble for plate tectonic theories, as they don’t fit with the general trend that most seismic and volcanic activity happens at margins. There are several examples of volcanic activity away from plate boundaries such as Yellowstone national park.
These hot spots are formed by huge columns of up swelling lava because of radioactivity within the earth, these columns are known as plumes. The plume of plastic molten rock that pushes upwards; causing pressure to drop and the plastic thin rock to become molten, melting and pushing through the crust above. These plumes lie in fixed positions under tectonics plates. As the plate moves over the hot spot, the upwelling lava creates a steady succession of new volcanoes that migrate across the plate. These plumes can be up to 1000km across.
The emperor sea mount chain is a good example of plume activity; showing the variation of activity within the succession as the plates move over the plume. This chain extends 5000km along the Pacific Ocean. The first hot spot seen in the chain is the Lohi volcano in Hawaii. Lohi is an active volcano submarine volcano. Due to subsidence and erosion overtime the volcano will become a flat topped submarine mountain known as Guyot. The Hawaiin volcanic island is the next formation in the sequence. This is an active volcano that as the plate moves away from the plume pressure will decrease causing it