Structure of Lō‘ihi Seamount, Hawai‘i and Lava Flow Morphology From High-Resolution Mapping

Abstract

The early development and growth of oceanic volcanoes that eventually grow to become ocean islands are poorly known. In Hawai'i, the submarine Lō'ihi Seamount provides the opportunity to determine the structure and growth of such a nascent oceanic island. High-resolution bathymetric data were collected using AUV Sentry at the summit and at two hydrothermal vent fields on the deep south rift of Lō'ihi Seamount. The summit records a nested series of caldera and pit crater collapse events, uplift of one resurgent block, and eruptions that formed at least five low lava shields that shaped the summit. The earliest and largest caldera, formed ∼5900 years ago, bounds almost the entire summit plateau. The resurgent block was uplifted slightly more than 100 m and has a tilted surface with a dip of about 6.5 • toward the SE. The resurgent block was then modified by collapse of a pit crater centered in the block that formed West Pit. The shallowest point on Lō'ihi's summit is 986 m deep and is located on the northwest edge of the resurgent block. Several collapse events culminated in formation of East Pit, and the final collapse formed Pele's Pit in 1996. The nine mapped collapse and resurgent structures indicate the presence of a shallow crustal magma chamber, ranging from depths of ∼1 km to perhaps 2.5 km below the summit, and demonstrate that shallow sub-caldera magma reservoirs exist during the late pre-shield stage. On the deep south rift zone are young medium-to high-flux lava flows that likely erupted in 1996 and drained the shallow crustal magma chamber to trigger the collapse that formed Pele's Pit. These low hummocky and channelized flows had molten cores and now host the FeMO hydrothermal field. The Shinkai Deep hydrothermal site is located among steep-sided hummocky flows that formed during low-flux eruptions. The Shinkai Ridge is most likely a coherent landslide block that originated on the east flank of Lō'ihi.

An intermediate-depth source of hydrothermal 3He and dissolved iron in the North Pacific

“…8c shows the Loihi-sourced 3 He profile as estimated by subtracting the average of "background" station profiles between 5 and 10 • N (station 21) and between 30 and 35 • N (stations 14 and 16). The helium isotope profiles nearest Loihi exhibit a significant 3 He signature between 900 and 1300 m depth with a maximum near 1100 m. The large vertical spread may be due in part to the topographic distribution of the many hydrothermal vent sites (Bennett et al, 2011;Clague et al, 2019;Rouxel et al, 2018) at Loihi. In addition, although diapycnal mixing in the open ocean is weak (Ledwell et al, 1998(Ledwell et al, , 1993, seamounts are known sites of enhanced vertical mixing (Lueck and Mudge, 1997;Toole et al, 1997).…”

“…The station over the Loihi Seamount was located at 18 • 54'23"N, 155 • 15'29"W, with a nominal depth of 1300 m, directly above the center of Pele's Pit (Clague et al, 2019), a collapse feature resulting from a 1996 seismic/eruption sequence (Duennenbier et al, 1997).…”

Hydrothermal Activity and Seismicity at Teahitia Seamount: Reactivation of the Society Islands Hotspot?

“…First, we note that the morphology of the seafloor at Teahitia as surveyed in 2013 (Figure 3) is remarkably similar to that observed in the original 1986 SeaBeam survey (Cheminée et al, 1989) with the same 4 peaks of the composite volcano prominent (TH1-TH4). Certainly, there is no evidence for the drastic changes in surface morphology (including pit collapse) observed at Loihi over the same time frame (Clague et al, 2019). More specifically, we also note that the shallowest summit of the TH1 cone in our 2013 survey is 1460 m (Figure 3) which coincides exactly with the depth at which submarine venting was located at the summit of this same cone in both 1989 (Michard et al, 1993) and 1999 (Hékinian, 1999).…”

“…Similarly large (M L > 4.0) earthquakes detected at Mehetia and Teahitia at the time of the 1981-1985 seismicity crisis were attributed to tectonic events, perhaps linked to seafloor volcanic pit collapse (Talandier and Okal, 1984). As such, that work accurately presaged exactly the processes that arose in association with seafloor volcanic activity at Loihi Seamount, more than a decade later (Davis and Clague, 1998;Clague et al, 2019). In their original Teahitia study, Talandier and Okal (1984) also noted that a comparable abundance of seismic tremors, similar to that witnessed during the 1980s, had only previously been detected on Tahiti in 1918 (Lespinasse, 1919).…”

Visual and Autonomous Survey of Hydrothermal Vents Using a Hovering‐Type AUV: Launching Hobalin Into the Western Offshore of Kumejima Island

“…Tuna-Sand, Tri-Dog 1, and Tri-TON operated at hydrothermal vent fields in Kagoshima Bay to acquire images of the seafloor (Maki et al, 2008;Nakatani et al, 2008;Sato et al, 2014). AUVs ABE and Sentry also conducted surveys using cameras (Clague et al, 2019;German et al, 2008;Yoerger et al, 2007), although visual observation was just a part of their missions. The aim of this work is to visually survey deep (∼1,000 m) hydrothermal fields using AUVs instead of HOVs/ROVs.…”