Lava tubes formation and extensive flow field development during the 1858 eruption of Mount Vesuvius. 

Lava tubes are an important transport mechanism in active lava flows. Their presence in a lava flow can influence its distance of emplacement due to the insulation of the hot molten lava by a cooled overlying crust. Understanding mechanisms of formation and development of lava tubes is fundamental to comprehend lava flow propagation and improve knowledge to better manage the hazard during a volcanic crisis. Vesuvius is known for its major explosive eruptions; however, in its history it underwent extensive periods of open conduit, with prolonged explosive activity and lava flows. After the 1631 eruption, Vesuvius entered an effusive period that ended with the 1944 eruption. During these 313 years, over one hundred lava flows emplaced on Vesuvius flanks, particularly the 1858 eruption which produced a compound pahoehoe lava flow that emplaced on the western flank of Vesuvius. In this study, we conducted: (1) a temporal and spatial reconstruction of the 1858 lava flow using historical documents (geological maps, paintings, descriptions of eruptions), (2) a morphological and surficial analysis of the 1858 lava flow as well as the definition of new contours based on geological maps and digital elevation models and (3) a complete morphological analysis of the lava tube using high-end technologies (time-of-flight terrestrial laser scanner, Lidar equipped drone and optical cameras).  On the 1858 lava flow field surface we found numerous tumuli and ephemeral vents. We discovered a small lava tube present in a flat area of the lava flow field (<3°) with ropy to slabby pahoehoe surface lavas. The lava tube is oriented north-south, perpendicular to the main flow direction. It is triangularly shaped with a length of 30.05 meters and a width that varies from 1.20 to 17.61 meters from the northern to the southern part. The average height is around 2 meters. The slope along the flow direction is on average 4.48°. We measured a mean roof thickness of 2.4 meters. The roof is fractured and has collapsed in different areas of the lava tube. Inside, we observed features that relate to the temporal evolution of the lava tube. Stalactites are present on the ceiling of the tube suggesting a prolonged flow of lava within the tube. Multiple layers of lava are covering the wall of the lava tube, the last wall lining is five to seven centimeters thick and, in some areas of the lava tube, has detached from the wall and rolled down on itself, testifying to a sudden drainage of the lava tube when the lining was still plastic.  The results of the study of the 1858 lava flow field and of its lava tube are essential for expanding our knowledge about the processes at the basis of lava flow field emplacement and development on Vesuvius and the first attempt focused on understanding effusive dynamics governed by lava tube formation (i.e., lava emplacement) at Vesuvius.