The correct answer is - Shield volcanoes.
The enormous volcanoes on Hawaii, Mauna Loa and Mauna Kea, are both shield volcanoes. They both have very broad and shallow slopes, and occupy a very large area because of it. These volcanoes are formed by a hot-spot, the Hawaii hot-spot, that manages to penetrate through the crust of the Pacific tectonic plate, and cause volcanic activity on this part of the world. Since the movement of the Pacific plate is drifting these volcanoes away from the hot-spot, over time they will stop being active, but other, new volcanoes will rise over the hot-spot,thus making the chain of volcanic islands even bigger.