Answer: volcanic activity
Explanation: The vast majority of volcanic activity on the planet occurs along the mid-ocean ridge, and it is the place where the crust of the Earth is born. The material that erupts at spreading centers along the mid-ocean ridge is primarily basalt, the most common rock on Earth.
Volcanic eruptions are formed when so much PRESSURE from the magma inside the volcano builds up to it's boiling point.
An example would be like shaking soda as soon as the pressure is released there is foam. It's then same concept but with magma aka lava
Hope this helped
<span>I think it's a. near china, north korea, and south korea </span>
