National Geographic Travelさんのインスタグラム写真 - (National Geographic TravelInstagram)「Photo by Robbie Shone @shonephoto | A tunnel formed by lava in 1792 extends inside Grotta Cassone, beneath the southern flank of Mount Etna, Sicily. Working in the tunnel, we established suitable survey stations and scanned all around the tube to create a 3-D map, incorporating all the striking basaltic features on the walls and ceiling. The lava that solidified on the floor has a corded, rippled texture. There are many similar lava tubes that have been discovered on Mount Etna as a result of road construction on the volcano.」10月22日 13時10分