Why are there so many volcanoes on earth?

rockyLucille

Hi Lucille,

There are two main types of volcanoes on Earth, so if you know why they occur then you can say why there are many volcanoes. The most common type of volcano is called either a strato-volcano or composite volcano or an arc volcano. These volcanoes are associated with subduction zones--places where an oceanic plate (such as the pacific plate) dives under another plate (such as the Asiatic plate). At such a boundary, the downgoing plate starts to melt, and this melt (called magma) migrates to the surface where it erupts to build a volcano. The Pacific ocean is ringed by subduction zones so it is no surprise that there are strato volcanoes also ringing the Pacific. The Pacific plate dives under Asia to produce the Kamchatka and Japan volcanoes. It dives under the Philippine Sea plate to produce the Mariana islands, under the Austrailian plate to produce New Zealand and Papua New Guinea volcanoes, etc. Subduction-related volcanoes comprise >60% of all the Earth's volcanoes.
Hotspot volcanoes are another relatively common type of volcano. We don't really know what a hotspot is, but we do know that hotspots produce magma at the surface, and that hotspots don't move, even with all the plate tectonic motion going on up on the surface. This makes them sort of like assembly lines for volcanoes. The best example is Hawai'i, where there are active volcanoes down at the southeast end and older and older volcanoes as you look further northwest (in the direction that the plate is moving).

If you want the fundamental reason for what is driving all this plate tectonic motion, and probably also the hotspots too, it is radioactivity. The Earth contains natural radioactive elements, and there are enough of them down in the deeper parts of the planet to produce a huge amount of heat as they decay. This is the ultimate engine that is driving the volcanic action at the surface. This does not mean that volcanoes are radioactive places. The concentrations, even down in the Earth, are very low. It's just that the Earth is big enough that there is enough material to produce a lot of heat.

I hope this helps to answer your question.

sincerely,

Scott Rowland 

Other Categories        Other Questions

To VolcanoWorld