Galapagos Islands
Galapagos geology
The islands are the peaks of gigantic volcanoes, composed almost exclusively of basalt. Most of them rise from 2,000 to 3,000m above the seabed. Eruptions have taken place in historical times on Fernandina, Isabela, Pinta, Marchena, Santiago and Floreana. The most active today are Fernandina, Isabela, Pinta and Marchena, and fumarolic activity may be seen intermittently on each of these islands.
Geologists generally agree that two relatively new geological theories explain the islands' formation. The theory of plate tectonics holds that the earth's crust consists of several rigid plates that, over geological time, move relative to one another over the surface of the earth. The Galapagos lie on the northem edge of the Nazca Plate, close to its junction with the Cocos Plate. These two plates are spreading apart at a rate of about 1 km every 14,000 years, and the Galapagos Islands are slowly moving southeast.
The hotspot theory states that deep within the earth are certain superheated areas that remain stationary. At frequent intervals, the heat from these hotspots increases enough to melt the earth's crust and produce a volcanic eruption of sufficient magnitude to cause molten lava to rise above the ocean floor and, eventually, above the ocean's surface. The Galapagos are moving slowly to the southeast over a stationary hotspot, so one would expect the southeastem islands to have been formed first and the north western islands to have been formed most recently. This has proven to be the case. The most ancient rocks yet discovered on the islands are about 3.25 million years old and come from Española Island in the southeast. In comparison, the oldest rocks on the western islands of Fernandina and Isabela Island are less than 750,000 years old.
While not every visitor has the time or energy to climb a volcano, a visit to one of the lava flows is within everyone's reach. Several can be visited, but the one at Sullivan Bay, on the east end of San Salvador, is especially rewarding. This lava flow is about a century old and remains uneroded. Here you can see pahoehoe, or 'ropy' lava, which is formed by the cooling of the molten surface and the wrinkling of the skin into ropy shapes by the flow of the molten lava beneath. Impressions of trees can be found in the solidified lava, and some of the first colonizing plants - the Brachycereus cactus and the Mollugo carpetweed - can be seen beginning the slow conversión of a lava fíeld to soil. continues...
Galapagos » Geology
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Galapagos Islands
Five of the islands are inhabited. The total population is certainly higher than the official figure...
