Site 5 - Largest lava tube

Located in a very flat area of the 1858 lava flow field, this lava tube is the largest one found in the 1858 lava flow field. The surface is characterized by an inflated pahoehoe flow showing longitudinal cracks and one skylight. The tube outer surface rises ≈1.5 meter above the ground, and is surrounded by vegetation. The tube entrance is through the skylight. The lava tube is 30 meters long, 1.5 to 17 meters wide and the mean height inside is 1.4 meters. Inside the tube there are lava stalactites, several inner linings, local collapses of the roof, and the floor is made of pahoehoe surface texture. Flow direction in the lava tube was from north to south. The lava entered from a small twenty-five centimetres wide vent and exited the lava tube to the southwest by a small passage. The mechanism that permitted this lava tube to form is different from the mechanisms described in the volcanological literature, and a new interpretative model was proposed by Lemaire et al. (2024) and used in the explanatory panel. The presence of a panel next to the site of interest is essential to the comprehension and dissemination of the characteristics and scientific information relative to the geosite. We developed a panel that first explains what a lava tube is, how these structures typically form and then explains how the observed lava tube (Site 5) is believed to have formed.