East of Reykjavik lies a mountain named Hengill. Hengill was formed from a Palagomite tuff and its highest point is around 800 metres above sea level. Hengill is a central volcano and has a giant magma chamber beneath it.
When the lava cools, it contracts. This is because hot things generally take up more space than cool things. Think about hot steam, for instance. When you open the lid of a simmering pot or a tea kettle, that hot steam wants to escape and expand into the air.
When thick basalt lava flows cool, they tend to form hexagonal cracks, called columnar joints. Among the world’s best-known examples of these “columnar basalts” are the Giant’s Causeway in Ireland and the Devil’s Postpile in California. No exposures of those scales exist in Hawaiʻi, but the columnar jointing in the Mauna Loa flow exposed at Boiling Pots, though small, provides a great opportunity to observe the result of lava’s cooling process.
The south coast of Iceland has so much to offer you. We start by driving south on Highway 1. We explain to you the geology of Iceland and show you many of the amazing and exciting places that have emerged in Iceland in both the past and present.