Tectonic boundary where two plates collide. Where a tectonic plate sinks beneath another plate and is destroyed, this boundary is known as a subduction zone. Subduction zones are marked by deep-focus seismic activity, strong earthquakes, and violent volcanic eruptions. An example of a subduction zone is along Japan, Alaska, and on the west coast of South America. If the two plates are both continental, and neither can subduct, they instead pile up at the boundary, creating high mountain ranges (the Himalayas, for example).