ナショナルジオグラフィックのインスタグラム(natgeo) - 6月2日 15時52分

Photo by @shonephoto (Robbie Shone) - The Grotta Cassone on the southern flanks of Mount Etna was formed more than 200 years ago, during the devastating 1792 eruptions, when a flow of relatively fluid lava cooled on the upper surface sufficiently to form a crust. Beneath the crust (which was solid like rock), the lava remained insulated, allowing it to continue to flow as a liquid. After a prolonged period of time, the lava conduit formed this tunnel-like aperture or lava tube that we see today.
Often these lavatubes drain out once the supply of fresh lava has stopped, leaving a considerable length of open tunnel within the lava flow. Sadly though, the cave is collapsing. Roots from plants growing on the surface have found their way down through small cracks and are now cracking the ceiling. Many similar lava tubes have been discovered on Mount Etna as a result of road construction on the volcano.

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