Morphology and structure of Loihi Seamount based on Seabeam Sonar Mapping

Abstract

Loihi seamount has been mapped using Seabeam multibeam sonar, and the resulting data have been processed to produce bathymetric maps with a 10‐m contour interval and shaded‐relief perspective images. Analysis of morphological and structural data recorded in the maps and images indicates that constructional volcanism on Loihi has been localized predominantly along its southern and northern rift zones and that these rifts have been active since early in the seamount's history. The distinct asymmetry between Loihi's eastern and western slopes (the eastern slopes are steeper) is attributed to mass wasting of large sections of the volcano's west flank. Two large amphitheater valleys on the seamount's west flank are believed to have resulted from repeated mass‐wasting events triggered by earthquakes associated with an early rift zone whose core now lies buried beneath the block feature present on Loihi's southwest flank. The prominent kink in the present south rift zone of Loihi may represent a fundamental readjustment of along‐rift magma conduits that was caused by gravitational slumping on the southwest flank of the volcano. Lava cones and constructional volcanic ridges are present along the rims of summit pit craters and form a continuous chain of volcanic constructs around the periphery of the summit platform. The concentric arrangement of young eruptive vents pn Loihi's summit may be caused by ring dikes. The morphology and structural interrelationships of pit craters on Loihi's summit suggest that the southeastern pit is the youngest. The formation of a summit platform on Loihi may have been caused by repeated collapse of pit craters and the southward migration of primary magma conduits that underlie the pits. This model predicts a north‐to‐south age progression for volcanism on Loihi's summit.