What do volcanoes tell us about the earth?

They tell us that we need to be carefull, when there is a warning about a eruption. It also tellls us about the earth in many ways, such as: There is lava under the the land layer, there are many tectonic plates, and so on.

Volcanoes tell us a lot about the chemical composition of rock. They tell us what incredible force there is under the earth's crust.

They can be used to indicate were the earth has been hit by large astroids in the past.

The shockwave from an astroide can go through the "core" to the opposite side of the earth and there cause an eruption.

Volcanoes tell us more about the past than our future.