The Galapagos Islands are an archipelago consisting of some 16 islands and numerous islets scattered over an area of nearly 36,000 square miles around the Equator. Each major island, with the exception of the largest island, Isabela, consists of a single large shield volcano. Isabela was formed from six volcanoes joined above sea level. The total land area of all the islands, islets and rocks that form the Galapagos Islands is about 3,028 square miles, with Isabela making up more than half the total land area, at 1,700 square miles. The islands all rose from the ocean floor as the tops of volcanoes, possibly during the Pliocene era, and have never been connected by land to any mainland area. Today, the Galapagos Islands remain one of the most active oceanic volcano areas on Earth.