Resolving the Thickness of Submarine Lava Flows in the North Arch Volcanic Field Using Magnetometry

Abstract

The North Arch Volcanic Field is a part of the greater Hawai’ian volcanic arch north of O’ahu. Only discovered in the 1960s; relatively little is known about it and the arch volcanism that formed it. One general property of basaltic lava flows is their relatively high remnant magnetization which distinguishes them from the surrounding, weakly-magnetized sediments. It was predicted that these flows would produce strong enough anomalies to be detected from surface level and that the resolved flows would have thicknesses in the 10s of meters. The ship followed a series of 5 track lines of 15-40 km heading in the east-west direction before traveling north-west along an inferred eruptive fissure. 29 lava flows were identified through sub-bottom profiler data. After collection, the data was processed in GRAV_MAG_PRISM, a modeling program which allows the user to break a magnetic body into prisms. Models were first created to assess what size lava flows would correspond to the average anomaly found in the data. Afterwards, one surveyed flow was modeled, and the prisms were manipulated to see if the modeled data could accurately match the collected data. Yielding thicknesses along the flow ranging from 5 to 50 meters, confirming predictions about their relative thickness. The results of this study demonstrate that magnetometry can be an effective tool for studying the North Arch Volcanic Field. In the broader scientific context, this also shows that magnetometry could be used on other submarine volcanic fields as well.