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:
- 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.
- 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:
- They dove following the above-described route.
- They encountered vents fairly early in the dive, but it was decided to
wait for a better vent field before starting to sample.
- 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.
- 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:
- The south end of Pele's Pit has not yet been investigated.
- 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.
- 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).
- A good approach for looking for the flows would be to go down the rift
in the sub to 1800 m and work upslope.
- Finally, due to the dangerous conditions, it looks like
single-observer/dual-pilot dives will be the rule.
27 Sept. 1996: Earlier info from the same expedition, also from Frank
Sanson (clarifying words added by the web page author are in s):
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.
9 Sept. 1996: The following special session has been added to
the line-up for the Fall AGU meeting in San Francisco this December 15-19
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.
Frank Sansone, Department of Oceanography, University of Hawaii, 1000 Pope
Road, Honolulu, HI 96822, Phone: 808-956-8370, Fax: 808-956-7112, E-mail:
and Paul Okubo, Hawaiian Volcano Observatory, Hawaii National Park, HI 96718,
Phone: 808-967-8802, Fax: 808-967-8890, E-mail:
For more information, visit the AGU meetings web page at:
30 Aug 1996: A seminar was held in a standing-room only auditorium
on the UH campus in which various expedition participants and other
scientists working on the recent seismic and tectonic activity at Loihi
described their preliminary results. Speakers were: Fred Duennebier, Jackie
Caplan-Auerbach, Brian Midson, Joe Resing, Xi Yuan Wen, Frank Sansone
and Ken Rubin. I (KR) present a brief summary here:
- 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
- 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
- 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
22 Aug 1996:
Mike Garcia has completed electrom microprobe analyses of glasses
from lavas collected on the recent event-response expedition. The
results and their interpretations are discussed on the
Rock Gallery page.
19 Aug 1996: Fred Duennebier announced
that there will be a special session at this Fall's AGU on the Loihi
Crisis and response. It will be Part II of the
Hawaii session organized by Mike Garcia and Paul Okubo.
If you'd like to give a talk, contact
one of them. Frank Sansone and Fred will probably be leading
this 2nd session. Think about abstracts!
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Last page update on 8 October 1996