Geomagnetic field intensity from Kilauea 1955 and 1960 lava flows: Towards a better understanding of paleointensity

Abstract

The record of the Earth’s magnetic field intensity during the past (paleointensity) carries important information about the geodynamo and the state of the Earth’s interior that is not contained in the record of its paleodirection. To determine what the critical factors in obtaining reliable estimate of paleointensity are, we present new results of a paleointensity study of the 1955 and 1960 Kilauea volcano lava flows, from the Big Island of Hawaii. Rock magnetic measurements on representative hand samples from each flow in conjunction with reflected light microscopy observations show the primary carriers of remanence to be pseudo-single domain titanomagnetite with various titanium contents. Paleointensity samples (small fragments previously embedded into salt pellets) were subjected to the Thellier-Coe experimental procedure. Fourteen temperature steps were distributed over the entire temperature range used (ambient temperature to 570°C). Control heating steps (commonly referred to as partial thermo-remanent magnetization — pTRM checks) were also conducted each third double heating step. Mean field intensity value (36.6 ± 0.7 μT) retrieved from 3 reliable site mean determinations reproduces the expected value within 1.1%. With the knowledge of the rock magnetic characteristics of the samples and the strength of the geomagnetic field during cooling of the lava, our investigation suggests that the Hawaiian lavas can faithfully record the local geomagnetic field and confirms that the Thellier-Coe type techniques are suitable on historical lava flows to yield reliable absolute paleointensity determinations. The variations in direct field measurements and in lab paleofield determinations may reflect local heterogeneities of the lava or influence of very local field anomalies due to the volcanic underlying terrain. These results underscore the importance that a better understanding of intensity results of historical lava flows is still required if reliable paleointensity determinations of older periods, for which we do not know the answer, are sought.