The Galapagos islands are geologically similar to the Hawaiian islands; both are archipelagos that were born and continue to be formed by lava flows originating from a volcanic hot spot. Lava from this type of volcano is high in basalt content, which affects both its flow properties and the formations it creates. Geologists have actually borrowed words from the Hawaiian language to describe the two main kinds of lava formations seen in basaltic flows: pahoehoe and a’a.
Pahoehoe formations tend to be relatively smooth and often leave behind a pattern of rope-like coils (below). In contrast, a’a lava features are sharp, rough, and challenging to traverse. Both flows are gravity-driven, and which features a given eruption forms depends on many factors. Many flows will even begin with a pahoehoe section that stretches for several kilometers before transitioning to an a’a structure. Researchers believe the transition occurs when the lava crystallizes enough to develop a yield-strength, meaning that it will behave like a solid until enough force is applied to make it flow again. Toothpaste, ointment, and mud are similar so-called yield stress fluids which will only flow after a critical force is applied. (Image credits: lava flow – Epic Lava Tours, source; pahoehoe lava – J. Shoer)
Galapagos Week continues tomorrow here on FYFD. Check out previous posts.