Galapagos Islands geological formations - Lava Caves & 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 the Tartar, described a spectacular eruption of Fernandina in 1825.