Volcanic formation of The Galapagos Archipelago!!!
The following informations are from various internet pages!!
Galapagos Islands Volcanic Formation – The islands of the Galápagos archipelago are formed by volcanic processes and continue to form with frequent eruptions. For example, Fernandina Island has had 14 eruptions in the last 37 years.
The hot spot is the origin of basalt lava which is born in the depths of the earth’s mangle where it ascends forming magma (melted rock) that reaches the surface of the planet giving rise to volcanoes.
According to the theory of tectonic plates, in the depths of the seas there is part of the surface of land that is not stable and it moves forming deposits of melted rock upon which the solid surface of the mantle forms a solid layer.(Photo: Pinnacle Rock)
A constant friction process exists between the rigid zone and the soft one which breaks the extrernal layer of the earth which forms tectonic plates.
The plate on which the Galápagos Islands are found is called the Nazca Plate and moves in the westerly-easterly direction.
Apparently the hot spots do not move in relation to the planet but the plates do. Thus, it is possible to build up chains of volcanic material under the water and occasionally islands such as the peaks of chains.
This is how the Galápagos Islands originated. The rocks that form the western party of Galápagos are very young (less than one million years old) but the chain extends from Galápagos to the edge of the Continent of South America (Carniege Chain). It is 22 million years old. These chains affect the movement of the underwater currents and the settling of sediments.
As land masses go, the Galápagos Islands are not very old. A little over four million years ago there was open ocean where they now lie, on the equator some 600 miles west of Ecuador. But submarine volcanic activity slowly built up the string of islands that Darwin visited in 1835. Indeed, it was Darwin who first recognized their volcanic origin, and who understood the profound implications of this origin for the history of life. For if the islands were volcanic, they must have formed after the creation of the world, and the organisms living there must have migrated there from someplace else. But since those organisms are found nowhere else, Darwin finally had to conclude that they had evolved there from South American ancestors.
After Darwin’s visit, and well into this century, the origin of the islands have been disputed. Many thought that they had once been part of the mainland, or connected to it by a land bridge. Eventually, however, Darwin was vindicated; these islands had a volcanic origin separate from the mainland and were never connected to it.
Plate Tectonics and the Formation of the Galapagos Islands
(Photo: Aerial view of islands)
But Darwin only had part of the answer. A more complete answer to the origin of the Galápagos could not be had until after 1958, when continental drift, or plate tectonics, were discovered. We now understand that the surface of the earth is divided into massive tectonic plates which slowly drift across the globe. The formation of the Galápagos is intimately tied to the history of the Nazca plate, on which they lie.
The Galápagos are located on the very northern edge of the Nazca plate, which is bounded by the Cocos (north), the Pacific (west), the South American (east), and the Antarctic (south)
plates (see map). The Nazca plate itself is currently drifting south, away from the Cocos plate, and east, away from the Pacific plate. Since the net direction of drift is southeast, the Nazca plate is colliding with the South American plate. At the point of collision, the South American plate, which is made of light continental crust, is riding up over the Nazca plate, which is made of dense oceanic crust. This type of plate interaction is called subduction.
As the Nazca plate is forced into the mantle, it melts and its melt products work their way up to the surface to form volcanoes. The land is further raised by the crumpling effect as the western edge of the continent rides up over the descending plate. The result of all of this is the Andes, a young, highly volcanic, rapidly growing mountain chain. This same movement of the Nazca plate is responsible for producing the cluster of volcanic islands we call Galápagos.
There is a large body of geophysical evidence for the existence of enormous plumes of hot mantle material that originate near the earth’s core and rise all the way to the crust. These plumes seem to be stable over many millions of years. and with time, they burn through the crust to form an underwater volcano which may eventually grow big enough to become an island.. But, because the crustal plate is in constant motion, the island will eventually move off of the hot spot. thereby making room for a second volcanic island. And a third, and a fourth…. Thus are archipelagos like the Galápagos formed.
Islands farthest from the hot spot are older and more eroded while islands near or on the hot spot are younger and steeper. Thus Isla San Cristóbal, the nearest to the mainland, is approximately four million years old and composed of eroded, rounded cones, while Isla Fernandina dates at less than 7000 years and is considered to be one of the most active volcanoes in the world. Recently former Galápagos islands, now submerged, have been discovered between Isla San Cristóbal and the mainland. This discovery may double the age of the islands. Indeed, several million years from now the present islands may likewise sink beneath the waves only to be replaced by a new set of Galápagos Islands. Who can imagine what course further evolution will take!?
Mid-ocean islands like the Galapagos are formed from basalt, the most basic of all types of lava. Basalt has a very different chemical composition from the lavas that erupt from continental volcanoes, and is much more fluid. Consequently, as the lava flows build up to produce a volcanic cone, the island cones have a much shallower slope than those on the mainland. These shallow-sloped volcanoes are called shield volcanoes and in the Galapagos, they are often compared to over-turned soup bowls. Such shield volcanoes can clearly be seen in the younger western islands of Isabela and Fernandina. To the east, the volcanoes are lower and more eroded.
Many volcanoes are topped by a caldera, a large circular depression derived from the original crater (sometimes this is subsequently filled in by new lava). During an eruption, the crater is fed from a magma chamber, but as activity dies down, the magma withdraws, leaving a large, open cavity. The ceiling periodically collapses, lowering the crater floor and widening the diameter. There was a major caldera collapse on Fernandina in June, 1968, when the floor dropped 300 meters! The largest caldera in the islands is that of Volcan Sierra Negra, Isabela, which is 7 by 10 km.
Lava Caves and Pit Craters
Two other volcanic features commonly seen by visitors are lava tunnels and pit craters. As lava flows downslope, the top often cools and forms an insulating crust that keeps the interior lava hot and running. As the eruption subsides, the molten lava drains out of the end, living a hollow chamber that can be many kilometers in length. These tubes have smooth sides with grooves that show different levels of lava. Such lava tubes can be seen in the highlands of Santa Cruz, and there is one just outside of Puerto Ayora. Pit craters are giant sink-holes that were never eruptive. These formed when subterranean magma chambers were emptied and the roofs collapsed. Classic pit craters are found at Los Gemelos in the Santa Cruz highlands.
The Galapagos Islands are considered to be one of the most volcanic regions in the world, and in recent years there have been small eruptions at Fernandina and Marchena. In 1979 there was a major, eruption of Volcan Cerro Azul. Benjamin Morrell, captain of theTartar, described a spectacular eruption of Fernandina in 1825.
Pit Craters, called father and son(one deeper and larger)
(Photos by: Houry Photography)