Accumulation rates of volcaniclastic deposits on Loihi Seamount, Hawaii

Abstract

AMS radiocarbon age dating of planktonic foraminifera in volcaniclastic deposits on Loihi Seamount yields ages ranging from 590 years before present (y BP) at 10 cm depth to 5,880 y BP at 1,007 cm depth in an 11-mthick section exposed along inward facing, calderabounding faults on the eastern side of Loihi's summit. The accumulation rate of the deposit was about 0.37 cm/y from 5,880 to 3,300 y BP and it consisted of subequal amounts of alkalic and tholeiitic fragments. The rate slowed dramatically at about 3,300 y BP to an average 0.04 cm/y and the particles that have accumulated since consist mostly of alkalic glass fragments. The decrease in accumulation rate could indicate a decrease in volcanic activity at Loihi beginning about 3,300 y BP. This lower level of activity appears to be continuing today.

No depth limit to hydrovolcanic limu o Pele: analysis of limu from Lō`ihi Seamount, Hawai`i

“…2) formed during a single eruption, or in successive eruptions, they effectively isolate the ash lens from the upper volcaniclastic layers. The upper layers contain particles of widely varying morphological types (of which limu is one) and glass chemistry (Clague et al 2003b); and a recent evaluation of sedimentation rates based on these layers indicates that they were emplaced over an estimated 5,000 years (Clague 2009). The limu and angular equant glass grains in the ash lens have identical chemistry, suggesting a single eruptive source.…”

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

“…More recent observations (Glazer and Rouxel, 2009) indicate that these vents have cooled significantly and are no longer depositing sulfides and sulfates. Part of the summit platform, particularly the eastern half, is covered by volcaniclastic deposits up to 11 m thick (Clague et al, 2000Clague, 2009;Schipper et al, 2011), which obscure the underlying lava flows and smooth the relief of the summit platform.…”

“…Highflux lava flows with channels and shallow collapses cover the summit platform E and NE of East Pit (one is labeled "flow" on Figure 10), but were trapped inside the inward facing scarps (R1, Figure 10) that define part of the R1 summit caldera. These flows, and others north of North Pit are buried by volcaniclastic sediment Clague, 2009;Schipper and White, 2010). Volcaniclastic sediment up to 11-m thick crop out at the tops of some of the outer caldera-bounding scarps (V, Figure 10), but were not observed on submersible dives inside the outermost caldera-bounding scarps.…”

“…P-A to P-D are pit craters described in the text and in Table 1. EP is East Pit, WP is West Pit, PP is Pele's Pit, C1 to C3 indicate two cones described in the text, S1 to S5 indicate the remnants of five lava shields, B indicates 1996 basaltic breccia, and V indicates volcaniclastic sediment 5-11 m thick Schipper and White, 2010) with a basal date of ∼5900 years (Clague, 2009). Arrow labeled "flow" indicates direction of channelized flow from S1 to the east.…”

“…The arcuate inward-facing ring fault on the northeast margin includes several steps (R1a and R1b, Figure 10) that may represent slumped portions of caldera walls, or two similar sized calderas. The base of an 11-m thick sequence of volcaniclastic sediment (V, Figure 10) exposed in the northeastern R1 scarp is 5900 years old (Clague, 2009), and formed before or during the collapse of the earliest and largest of the recognized calderas.…”