SEED Science


The Earth — A Living Planet
The Ring of Fire

 

Ring of Fire

Courtesy USGS

Earthquake epicenters around the Pacific Ocean

What is the Ring of Fire? No, it is not a new wrestling championship — it’s the name of a geologic phenomenon surrounding the Pacific Ocean. The Ring of Fire is the location where most of the seismic activity in the world is taking place. The Pacific Ocean has a mid-oceanic ridge and is surrounded by subduction zones. The spreading rate of the ridge is very fast. As a result, the subduction zones need to destroy a lot of crust. This is why there are so many earthquakes and volcanoes all around the rim of the Pacific Ocean, where the subduction zones are located.

The Pacific Ocean also has a group of volcanoes at Hawaii. However, Hawaii is not located at a plate boundary. Some scientists explain this as a "hot spot," but this explanation is not universally accepted.

 

Is Hawaii a hot spot?

Hawaii is not just a hot spot for holidays — it is also a geophysical hot spot. The existence of hot spots is probably one of the most controversial points in plate tectonics.

 

Hot Spot

Courtesy USGS

Artist's conception of the movement of the Pacific Plate over the fixed Hawaiian "Hot Spot," illustrating the formation of the Hawaiian Ridge-Emperor Seamount Chain. (Modified from a drawing provided by Maurice Krafft, Centre de Volcanologie, France).

According to the hot spot theory, an unusual event taking place at a point inside the Earth forces magma to go up to the surface. The magma always goes to the same place, but it arrives at random intervals of time. As the oceanic crust moves over the hot spot, the lava does not come to the surface at the same location every time. The Hawaiian archipelago (chain of islands) follows the general movement of the oceanic crust. According to this theory, each island was created in turn by intense volcanic activity, followed by a long period of silence. Another point in favor of this explanation is the pattern of volcanic activity of the islands. Only the island of Hawaii, the last island in the archipelago, is still an active volcano.

How is this possible? Once again, there are several different theories. No single theory is definitely correct. One that is widely accepted is that convection currents in the asthenosphere cause the hot spots. (The asthenosphere is the semi-solid layer of the mantle beneath the lithosphere, the outer layer of crust and stiff mantle.) Major plate movements are thought to be due to the huge currents moving around within the enormous amount of rock in the mantle. Hot spots are believed to be caused by a similar occurrence on a smaller scale. The hot spots stay in one place relative to the plate moving above them.

 

Athenosphere

Courtesy USGS

Hot spots are thought to be caused by convection currents in the asthenosphere, a semi-solid layer beneath the lithosphere, the stiff outer layer that includes both crust and mantle rocks.

Convection currents moving in different directions create a weak area in the lithosphere. The magma breaks through the weak spot to reach the surface and create a volcano. Why doesn’t this happen all the time? Why does volcanic activity stop for a while and then start up again? These questions are still part of the mystery of hot spots.

For more information about hot spots, visit pubs.usgs.gov/publications/text/hotspots.html


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