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Geology of the Galapagos Islands

Hot magma breaking through the seafloor slowly built up submarine mountains that eventually reached the surface and whose peaks form the 13 primary islands of the Galapagos today. The Hot Spot below the oceanic plate that emitted the magma is stationary, so as the ocean plate moves east toward South America the older islands move eastward too, and new islands form on the western edge of the archipelago.

The landscape of every island in the Galapagos is dominated by majestic and ruggedly beautiful volcanic forms: huge bowl-shaped shield volcanoes with gentle slopes produced from a large fluid lava flows; cinder cones with the classic conic silhouette formed by gas-rich, explosive eruptions; tuff cones created when lava erupts directly into water resulting in a smooth compacted ash; collapsed craters called calderas (Oregon's Crater Lake is the best known caldera in the US); and lava tubes formed when molten lava flows crust over leaving a liquid core that later drains leaving circular tunnels up to 30 feet in size. On many of our shore excursions we hiked over immense lava flows known as lava deltas, which solidified as they fanned out on land in their journey to the sea. The Hawaiian name for this lava is Pahoehoe Lava (pronounced "pahoyhoy") which means "ropy" lava, a name that derives from the rocks' interesting rope-like forms.

Bartolome, one of the driest islands we visited, gets almost no rain (the few plants live on the dew they collect each morning) and one of our shipmates joked that NASA could have used the island to stage the Rover's landing on Mars.