The Incredible Geology of the Galapagos Islands
Volcanoes, which have risen above the ocean surface, make a unique setting for this memorable visit. The most recent eruption was on Isabela in May of 2008. However, the evidence of past eruptions is visible everywhere. Lava fields still dominate the landscape of a number of islands, ash pockets remain untouched and the dramatic black sand covers many beaches.
As the plates shift over the hot spots below, new volcanoes that eventually become islands are formed. Due to this progression, the islands in the west of the archipelago are the newest and therefore tallest. The older volcanoes to the northeast have been more weathered and worn down. The islands consist only of basalt unlike the variety of rock types found on the mainland.
A hot spot is a location where magma thrusts up against the bottom of a continental plate, melting the solidified substance and, when it is able, to escape trough cracks or weak spots. At this point it may either leak out, spreading slowly across the earth's surface, cooling to form basalt or erupt creating an immense release of gas, steam and ash which create "tuff" deposits.
Volcanoes are active for a duration of roughly 500,000 to 1,000,000 years. They are formed by the slow build up of cooling magma layers on top of each other after each eruption. Eventually it will surface above the ocean, forming an island. With time, the plates shift and carrying these volcanic islands away from the hotspot. At this point they become inactive. The elements wear at the surface over time, eroding the rocks and smoothing the jagged edges.
Often the plate a volcanic island resides on sinks as it cools. This, in combination with the elements, result in the slow 'sinking' of the island. Once it is no longer above sea level, it is known as a "gyote."
But as one island is sinking, another is forming to the west, keeping the island chain intact. Over eight million years ago, the Galapagos were formed, but the chain itself could be even older. The oldest island that remains above the surface is more than three and a half million years old.
