Lava pillar distribution at the East Pacific Rise (9[degrees]09' to 54' N) and Axial Volcano, Juan de Fuca Ridge, 1998 lava flow

This study examines if and why submarine lava pillars show indications of clustering at 2 specific mid-ocean ridge study areas: the East Pacific Rise (EPR) from 9°09' to 54' N; and the 1998 lava flow at Axial Volcano, Juan de Fuca Ridge (JFR). Data from dive video, dive video logs, and existing data were used to map and analyze pillar distributions. Then simple scan statistics in conjunction with the video log observations were used to determine that lava pillars at the both the study locations are not randomly distributed. Pillars at the EPR are located mainly within the boundaries of the Axial Summit Trough. Pillars at the Axial Volcano 1998 flow are likely to be found in areas containing collapse pits and are most concentrated directly adjacent to, but not within, a sheet flow at the bottom of the main collapse area that is located through the center of the 1998 flow. Four reasons why pillars may or may not be found at a specific locations include: (1) conditions were not right for pillar formation; (2) pillar formation originated but then failed before formation was complete; (3) pillars formed but were subsequently destroyed; (4) pillars exist at a location but are unable to be observed due to conditions of bathymetry. Flow characteristics and eruption parameters likely determine if a particular location will tend to display lava pillars.