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The islands that are visited on Galapagos cruises are the peaks of immense Galapagos Islands volcanoes submerged beneath the sea. While we are not likely to see an actual eruption (last eruption was on May 2008 in Isabela Island), we will see the results of past volcanic activity everywhere on the islands. The lava flows and ashbeds, the craters and volcanic necks, even the black sand beaches are all signs of the volcanic activity that continues even today on the western islands.

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The volcanic islands of the oceans are a very different landscape from what we see in the crumpled and folded mountains of the continents. The Galapagos Islands are a long chain of isolated volcanoes set on a flat sea floor.

The western end of this chain has the tallest and youngest volcanoes while the progressively smaller and older volcanoes extend to the northeast towards South America. The Galapagos volcanoes are also composed of basalts and basaltic "tuffs" rather than the many different kinds of rocks found on the continents.

The Galapagos Islands, like the Hawaiian islands, lie over a hot spot, a place where a plume or column of very hot material rises from deep in the Earth's interior and pushes up against the bottom of a rigid crustal plate. The top of a mantle plume may be 30 miles in diameter and while it does not melt through the crust, molten rock from it may flow up through cracks to the surface. At the surface the molten lava spills out to form flows that cool and become the rock we call basalt, or it may explode as clouds of gas, steam, and ash to from tuff deposits.

Galapagos Islands Geology Volcanoes