The largest is Mauna Loa on the Big Island of Hawaii. Shield volcanoes can be so large they are sometimes considered a mountain range, such as the Ilgachuz Range and the Rainbow Range, both of which are in Canada. These shield volcanoes formed when the North American Plate moved over a hotspot similar to the one feeding the Hawaiian Islands, called the Anahim hotspot. There are also shield volcanoes, for example, in Washington, Oregon, and the Galapagos Islands. The Piton de la Fournaise, on Réunion Island, is one of the more active shield volcanoes on earth, with one eruption per year on average.