What Makes Them Erupt?

WE ARE awestruck as we see pictures of volcano eruptions. At the same time, we wonder, ‘What is going on underneath?’

Geophysicists do not know exactly what is going on underneath. According to the theory of plate tectonics, however, the entire surface of the earth is divided into several large plates. These plates move like conveyor belts toward boundaries with other plates, and one slips under the other at the boundary. If an ocean plate slips under a land plate, pressures and temperatures rise. As the water in ocean plates is squeezed out, it reduces the melting point of rocks. If the temperature is high enough, the rock will melt into magma.

Molten rock, or magma, is forced upward and accumulates in a reservoir some miles below the surface of the ground. When pressure builds up in the magma reservoir, it is released through eruptions. Depending on the type of molten rock and its gas content, eruptions blow off tops of mountains, cause explosions of steam and gas, or spew out lava.

Though geophysicists have delved extensively into the mechanism of volcanoes, they still do not know the details as to how magma is formed. When it comes to knowledge concerning the formation of mountains, we still cannot answer the challenge the Creator put to Job: “Where did you happen to be when I founded the earth? Tell me, if you do know understanding.”​—Job 38:4.

[Picture Credit Line on page 31]

Inset photos: C. W. Stoughton/​National Park Service