https://phys.org/news/2018-05-hawaii-volcanoes-addition-kilauea.html

WHY DOES HAWAII HAVE SO MANY VOLCANOES?

The Hawaiian Islands are a chain of volcanoes formed over millions of years. They've developed as the Pacific Plate—one of more than a dozen tectonic plates on the earth's outer layer—slowly moves northwest over a stationary hot spot of magma under the earth's surface. The hot spot partially melts an area under the Pacific Plate, sending magma to the ocean floor. Over time, lava accumulates and emerges above the ocean and builds islands.