Earthquakes are related to volcanic eruptions because when an earthquake happens, two tectonic plates rub against each other. Beneath these tectonic plates is molten lava, or magma. When the two tectonic plates rub on each other, it causes an earthquake, and the magma exerts extreme pressure on the rock, making it to crack. For every crack, there is an earthquake. The crack allows the magma to shoot up, either making it's own volcano under the sea, or forcing another volcano to erupt.