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The Galápagos Island region is one of the most volcanically active areas in the world. The first islands were formed between three and five million years ago, when underwater mountains formed by successive volcanic eruptions began to emerge from the sea. Island formation following the same process has continued ever since. Since 1535, when the islands were discovered, over 50 eruptions have been recorded, the most recent of which just occurred on Fernandina in May 2005.
Geologists use the theory of plate tectonics and the hotspot theory to explain the formation and evolution of the Galápagos Islands . According to the theory of plate tectonics, the earth's outer crust is comprised of a series of dynamic terrestrial pieces, or plates, which move with respect to one another in one of three patterns: they can spread apart, slide past, or collide with one another. Near the Galápagos, tectonic activity follows an interesting yet complicated pattern influenced by the convergence of three plates—the Pacific, the Nazca, and the Cocos Plates. The island archipelago is located on the northern boundary of the Nazca Plate near its junction with the Cocos Plate, but it is not at rest there. Sea-floor spreading along the Galápagos Rift causes the islands to move south and east at the rate of 7cm/year.
The hotspot theory says that certain stationary points within the mantle, the earth's middle layer, have the unique capability of periodically superheating. When the heat from these areas increases enough to melt the crust, a volcanic eruption will result with enough strength to drive molten lava above the ocean's surface. As tectonic plates move across the fixed hot spot, a trail of volcanoes will follow, each aging and eroding with time. Since the Galápagos are moving southeast over the hot spot, geologists have determined that the oldest islands must be San Cristóbal and Española, in the southeast archipelago, and the newest islands must be the northwestern islands of Fernandina and Isabela. In fact, these islands, which are situated directly over the hot spot, are still in the process of formation.
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