The subducting plate, as it goes down deep into the mantle, releases water. This changes the chemistry of the already hot rocks in the mantle and causes them to melt, forming magma. The magma is less dense than the solid rocks around it, so it rises upward, culminating in volcanic eruptions at the earth's surface.
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The subducting plate, as it goes down deep into the mantle, releases water. This changes the chemistry of the already hot rocks in the mantle and causes them to melt, forming magma. The magma is less dense than the solid rocks around it, so it rises upward, culminating in volcanic eruptions at the earth's surface.