One of the biggest questions yet to be answered about plate tectonics is how do subduction zones start? A subduction zone is a deep trough cut across the ocean floor. They form when two tectonic plates collide and one of the plates is pushed under another as they move towards each other, creating an ocean trench.
When the tectonic plates collide the underlying plate is consumed into the Earth’s mantle, creating a hot magma that erupts from volcanoes on the surface of the overlying plate. These volcanoes form a volcanic arc.
There are examples of this kind of natural occurrence all across the globe. One is the Izu-Bonin-Mariana Arc (IBM), an extinct arc bordering a trench zone south of Japan.