What is the name for an underwater volcanic eruption that creates new land?

The correct answer is seafloor spreading, which refers to the process that occurs at mid-ocean ridges where tectonic plates are moving apart. As these plates separate, magma from the mantle rises to fill the gap, leading to volcanic activity. When this magma erupts underwater, it solidifies and contributes to the formation of new oceanic crust, effectively creating new land.

This process is significant because it continuously reshapes the ocean floor and can lead to the development of new islands over time as eruptions build up layers of rock. Seafloor spreading is a fundamental part of plate tectonics and illustrates how geological processes can shape the Earth's surface.

In contrast, subduction involves one tectonic plate being forced under another, which does not directly create new land. The mid-ocean ridge is a geographic feature that is created by seafloor spreading but is not the name for the eruptive process itself. A tsunami, while often caused by underwater volcanic eruptions or earthquakes, does not create new land.