The origin of Mauna Loa's Nīnole Hills: Evidence of rift zone reorganization

Abstract

In order to identify the origin of Mauna Loa volcano's Nīnole Hills, Bouguer gravity was used to delineate density contrasts within the edifice. Our survey identified two residual anomalies beneath the Southwest Rift Zone (SWRZ) and the Nīnole Hills. The Nīnole Hills anomaly is elongated, striking northeast, and in inversions both anomalies merge at approximately −7 km above sea level. The positive anomaly, modeled as a rock volume of ~1200 km3 beneath the Nīnole Hills, is associated with old eruptive vents. Based on the geologic and geophysical data, we propose that the gravity anomaly under the Nīnole Hills records an early SWRZ orientation, now abandoned due to geologically rapid rift‐zone reorganization. Catastrophic submarine landslides from Mauna Loa's western flank are the most likely cause for the concurrent abandonment of the Nīnole Hills section of the SWRZ. Rift zone reorganization induced by mass wasting is likely more common than currently recognized.

Shallow Volcano‐Tectonic Structures on the Island of Hawai'i Imaged by Multimode Rayleigh Wave Ambient Noise Tomography

“…Using a more realistic three-dimensional inversion, Flinders et al (2013) show that the high-density structures beneath Mauna Loa are more concentrated toward MLNRZ, not the upper MLSWRZ, which is in accordance with our result and previous body wave tomography result (Park et al, 2009). As for the lower MLSWRZ, it has both high density (Denlinger & Flinders, 2022;Kauahikaua et al, 2000;Zurek et al, 2015) and high velocity (Monteiller et al, 2005;Park et al, 2009), but out of our well-resolved region. The orange region in panels (a and c) denotes the deep rift zone where the magma intrudes into and transports horizontally from the summit (perpendicular to the plane of paper), before rising to form eruptions.…”

“…(2013) show that the high‐density structures beneath Mauna Loa are more concentrated toward MLNRZ, not the upper MLSWRZ, which is in accordance with our result and previous body wave tomography result (Park et al., 2009). As for the lower MLSWRZ, it has both high density (Denlinger & Flinders, 2022; Kauahikaua et al., 2000; Zurek et al., 2015) and high velocity (Monteiller et al., 2005; Park et al., 2009), but out of our well‐resolved region.…”

“…Consistent with this interpretation, MLSWRZ and MLNERZ are relatively recently developed rift zones. Previous studies have suggested that an older south‐trending rift zone of Mauna Loa migrated over time to become today's MLSWRZ (J. K. Morgan et al., 2010; Zurek et al., 2015). The migration may have been initiated about 0.1–0.2 Ma ago, based on the ages of the older Nı̄nole basalt (Lipman et al., 1990) and the time of ‘Ālika 2 landslide (G. W. Moore & Moore, 1988), and Mauna Loa is likely to have less frequent eruptions thus less shallow dike intrusions in the last 0.1 Ma (Lipman, 1995).…”

“…During the process, built‐up stresses within the flanks could be released either gradually, through slow‐slip events (Brooks et al., 2006; Cervelli et al., 2002; Montgomery‐Brown et al., 2009; Segall et al., 2006), or abruptly, through major earthquakes along the basal décollement fault (Lipman et al., 1985; Neal et al., 2019; Wyss, 1988) and landslides (J. G. Moore et al., 1989; J. K. Morgan et al., 2003). In turn, large‐scale landslides can significantly change the stress field, potentially causing the rift zones to be abandoned or reconfigured (J. K. Morgan et al., 2003, 2010; Zurek et al., 2015).…”

“…, or abruptly, through major earthquakes along the basal décollement fault (Lipman et al, 1985;Neal et al, 2019;Wyss, 1988) and landslides (J. G. Moore et al, 1989; J. K. Morgan et al, 2003). In turn, large-scale landslides can significantly change the stress field, potentially causing the rift zones to be abandoned or reconfigured (J. K. Morgan et al, 2003Morgan et al, , 2010Zurek et al, 2015).…”