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When an earthquake begins deep inside the Earth, the waves go through water as well as land.
When the waves hit the shore, they often do more damage than the quake alone.
Volcanic eruptions can come with earthquakes, too. That happens more often under the ocean than on land. Deep trenches form on the ocean floor when plates push against each other and one is forced under the other, causing an earthquake. Some of the molten rock under the Earth’s crust then pushes up and out, causing an eruption.
When one plate is forced below another, the process is called subduction. Some of the Earth’s crust is pulled into the mantle, and some of the soft, hot rock in the mantle rises up to become crust.
