Investigation of lava flow morphology using a sub-bottom profiler in the North Arch Volcanic Field

Abstract

Located 100 km north of Oahu and over four kilometers of water, the North Arch Volcanic Field covers an area of 25,000 km2 and includes the longest known underwater lava flow. There have been a few previous studies of the area, but overall, the volcanic field is not well understood. Further classification the flow morphology of these lava flows can contribute to the understanding of the history of volcanism within the area, as well as marine effusive lava flows. A transect was mapped within the southernmost part of the field using 30 kHz EM302 multibeam echosounder and 3.5 kHz Knudsen echosounders aboard the R/V Thomas G. Thompson. These surveys yielded a high-resolution bathymetric map and sub-bottom profiles that image shallow structures beneath the ship’s track. The seafloor is 300 meters shallower within the northern parts of the study area, as the transect moved onto the Hawaiian Arch. The lava flows here are more extensive and presumably closer to the eruptive source. Through the analysis of the Knudsen data, 29 lava flow crossings were found that vary in width and height. The lava flows have complex flow morphology, including different boundary structure, sediment pockets, and complex flow paths and elevation changes. There are two main areas of flows within the southern part of the study site with differing characteristics that may be related to the lava viscosity. The lava field is more variable than expected, which suggests that even in the small region sampled, it was formed by several effusive events over a period that had lava with different chemical properties.