During volcanic eruptions, spectacular caves, called tubes (or tunnel) of lava. These structures form only under certain conditions, particularly in the presence of washes very fluidly. They can be even tens of kilometers long and often have openings that make them visitable. Lava tubes are widespread throughout the world, particularly in the Hawaiibut they are also numerous in the solidified flows ofEtna. These tunnels are not exclusive to our planet, but have also been detected on Mars and the Moon.
How lava tubes originate and are made
Lava tubes originate when, during an eruption, a volcano emits a basaltic lava flowwhose characteristics are high fluidity and a very high temperature (1100-1200 °C). The lava, being so fluid, flows rapidly along the sides of the volcano and over time begins to cool at the sides of the flow and solidify, forming increasingly greater thicknesses. The lava also solidifies in the upper part of the flow, forming a crust that acts as aroof”: thus a kind of tunnel is created, inside which the lava continues to flow towards the valley. Thanks to this insulation, temperatures remain high in the tunnel and the casting can travel long distances before cooling. When the eruption ends, the lava solidifies completely, the tube empties and becomes a grotto. Over time, the roof of the lava tube can collapse, exposing its interior.
Lava tubes feature i shield volcanoeswhich have slightly steep sides, ei basaltic plateauxvast flat plateaus originating from the very fluid lava emitted by linear volcanoes. These caves usually have a subhorizontal development and are often accessible thanks to the fact that their entrance is located close to the surface. Inside them there are lava stalactites and stalagmites, similar to those of karst caves but of different origin.
In lava tubes there are extreme conditions that might seem incompatible with life. In reality, however, here lives ahuge variety of microorganisms which feed on chemicals present in rocks. Similar extreme conditions also characterize the lava tubes present on Marsso their study provides information for the search for life forms on the red planet.
Lava tubes in the world
The most famous and longest lava tubes in the world are located at Hawaiian Islandswhere shield volcanoes erupt very fluid basaltic lava. The primacy belongs to Kazumura Caveover 65 km long and located on the slope of the Kilauea volcano on Hawaii island, the largest in the archipelago. This structure was formed inside a flow dating back 500 years.
Even at Canary Islands there are important lava tubes. On the largest island of the archipelago, Tenerife, there is the Cueva del Vientothe sixth longest lava tube in the world and the largest in the European Union. It was formed in the flow of the Pico Viejo volcano and is made up of various levels which make it particularly complex. Fossils of extinct prehistoric organisms have been found inside.
Even theIceland it is rich in these structures, located in the basaltic plateaus that originated from the eruptions of numerous linear volcanoes. Among the best known are the Surtshellir-Stefanshellirwhich means “giant fire cave”, 3.5 km long, and the Viögelmirover 1.5 km long and with a diameter of up to 27 m.
In Italy, the basaltic flows ofEtna they host countless lava tubes, ranging from a few tens of meters to over a kilometer long. One of the best known is the Three Levels Cavewhich features three tunnels one above the other.
