Recent Activity at Loihi Volcano

Loihi Events 18 Aug -31 Sept. 1996

Current Geologic Activity and Research at Loihi

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30 Sept. 1996: Frank Sansone provided this summary of observations presently being made using the PISCES V submersible, which is back at Loihi for the first time since the Event Response Cruise in August. This info comes to him via telephone conversations with researchers presently aboard the R/V KOK at Loihi (clarifying words added by the web page author are in []s):

Alex Malahoff's dive of 9/27:

1. They established a route to the new vents on the west wall of Pele's Pit. It involves landing in the sand channel between the 2 interconnected pits, moving into Pele's Pit, and then heading upslope to the vents.
2. They then went to the area north of the pits (the source of the noise that Fred heard with the sonobuoys last month). This area used to be the site of numerous volcanic mounds, but is now a talus slope dipping to the south into East (I believe) Pit. Alex reported seeing the remnants of an old dike that had "exploded".

Jim Cowen's dive of 9/28:

1. They dove following the above-described route.
2. They encountered vents fairly early in the dive, but it was decided to wait for a better vent field before starting to sample.
3. Subsequently, much time was lost due to travel up dead-end canyons, etc. One hour before the scheduled end of the dive the sub brushed an unseen wall and one of the thrusters was damaged; the dive was then aborted with, unfortunately, no samples collected.
4. The thruster damage has been repaired using parts on the KoK. Jim will have another dive tomorrow (9/30), the last for this leg. We will be bringing a backup thruster duct to the ship on Tuesday so there will be a spare for the next dive series.

Further notes from Alex Malahoff:

1. The south end of Pele's Pit has not yet been investigated.
2. Irena reports seeing a secondary Mn in the water column at approx. 2000 m depth (data from shipboard analyses of hydrocast samples). This plume was undetectable from CTD temperature measurements.
3. Alex agrees with the [hypothersis] that the collapses seen at the summit indicate that volcanic activity should have occurred downslope. He is convinced that it has taken place on the south rift (and may still be occurring, as evidenced by the Mn plume at 2000 m).
4. A good approach for looking for the flows would be to go down the rift in the sub to 1800 m and work upslope.
5. Finally, due to the dangerous conditions, it looks like single-observer/dual-pilot dives will be the rule.

    Briefly, the Sea Beam worked just fine with the new bow-thruster covers. [Bubbles associated with the latter had made Sea Beam imaging difficult on the earlier event respone expedition]. Fred [Duennebier] still hears some noise with the sonobuoys, but it's much further north now. The visibility in the pits has cleared up, but now you can see how dangerous they are (lots of sliding debris -- today the [divers] got caught in a mud slide in East Pit).
    Yesterday they [the divers] went to Pele's Pit and DID find venting on the bottom, but felt it was too dangerous a place to work in. They then went to the summit area north of East Pit (where Fred heard lots of activity last month), but they found no evidence of volcanic activity, just lost of broken up pillows. The glassy material they found appeared to be from broken pillows. Finally, they visited West Pit, but found no activity -- however, they did see a number of columnar basalts that appeared to be teetering due to collisions from debris slides.
    Today they went to East Pit, but found no venting. The visibility was not good due to particles that appeared to be coming from Pele's Pit via the channel that connects the two pits. They then looked for vents in Pele's Pit at around a depth of 1160 m (the depth of the plumes they found with tow-yos). They found active venting at that depth on the upper west (I believe) wall below Pele's Lookout. However, because of the steepness of the slope, dives that hope to work at that site will need 2 pilots -- 1 to keep the sub in position and 1 to operate the manipulators.
    Tomorrow they intend to map a safe route to these later vents, and they will investigate the "noisy" area to the north of the summit.

OS15     The Loihi Seamount Seismic Event of 1996: Event Detection, Rapid Response, and Follow-Up Cruises (Joint with S and V)
Starting in July 1996, the largest swarm of earthquakes ever recorded from any Hawaiian volcano was detected from Loihi Seamount, which is located offshore of the island of Hawaii.
Over 4000 earthquakes were recorded by the Hawaiian Volcano Observatory, with more than 40 having magnitudes between 4 and 5. A rapid response cruise and submersible dives were conducted during August 5 - 9, and follow-up cruises and dives are scheduled for September 23 - October 10. The initial cruise and submersible dives detected, sampled and mapped highly altered hydrothermal plumes; recorded seismic events in the summit region using a hydrophone and sonobuoys; mapped large-scale bathymetric changes; and collected rock samples for geochemical analysis. This session will offer an interdisciplinary opportunity to examine the seismic events, the vent fluid and rock geochemistry (including the evidence for volcanic activity), the evolution of the hydrothermal fluids, the structure and dynamics of the hydrothermal plumes, and structural changes associated with the event.

Conveners: Frank Sansone, Department of Oceanography, University of Hawaii, 1000 Pope Road, Honolulu, HI 96822, Phone: 808-956-8370, Fax: 808-956-7112, E-mail: sansone@soest.hawaii.edu ; and Paul Okubo, Hawaiian Volcano Observatory, Hawaii National Park, HI 96718, Phone: 808-967-8802, Fax: 808-967-8890, E-mail: paul@tako.wr.usgs.gov

For more information, visit the AGU meetings web page at: http://www.agu.org/fm96call.html

• Video images of the summit region showed a highly disupted surface containing debris of many sizes, fining away from the pit craters. In some areas, chunks of fresh, glassy, black basalts were inter-strewn amongst older, more altered lavas. These deposits appear as secondary, as the fresh basalts are not pytoclastic in origin, and are rather likely redeposited pillow fragments
• Earthquakes have been analyzed and the slow process of precisely locating them on the seamount has begun. A cluster of activity during the sawrm occured around 10 km depth and activity trends along Loihi's predominant rift zone.
• Water chemistry shows distinct geochemical anomalies, including pH as low as 5.5 and very elevated Fe and Mn concentrations. An upper water-column signature of plume-activity was found, as well as extreme geochemical indications for large scale fluid injections into waters below the sill depths of the pit craters on the summit.
• Particulates filtered from the water column sampling show heterogeneous compositions (by XRD). Their concentrations in various water samples correlates positively with water temperature.
• Discussion of rocks collected on this expedition centered around the fact that although the 7 samples ranged in visual appearance from fresh to altered, they have essentially the same chemical composition. This is in contrast to previous expeditions to Loihi that have brought back rocks of a wide range of compositions. Deteremination if any of these rocks were erupted during the recent activity at Loihi awaits radiometric dating underway at UH

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This page created and maintained by Ken Rubin,© krubin@soest.hawaii.edu

Last page update on 8 October 1996