Events During 1 to 31 October 1996
Current Geologic Activity and Research at Loihi
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11 Oct. 1996: Frank Sansone provided these reports from aboard ship of observations presently being made using the PISCES V submersible, which is back at Loihi for the second time since the Event Response Cruise in August. Please Note: If additional information on this expedition is needed, Frank can be reached by email ( sansone@soest.hawaii.edu) or phone (808-956-8370). He will be out of the office Oct 16 - Nov 6.
LOIHI SCIENCE REPORT -- Friday, October 11, 1996
From the scientific party on the research ship Ka'imikai o Kanaloa at
Loihi Seamount, Hawaii -- The LONO cruise (Loihi Oceanographic Neo-tectonic
Observations)
First, a correction and amplification from (last) Wednesday's report (our shot in the hyperbole war!): "Beyond marker 2 it's all box canyons, pillar trolls and overhang monsters, with sub-punching boulders the size of buses." -- Terry Kerby, Sub Pilot (and Operations Director)
The hydrothermal site sampled Tuesday at a depth of 1196 m on the south rift
has been confirmed to be a new field. It has been named Pohaku (rocky) vents.
Wednesday's dive operations focused on completing work at Lohiau vents. In
addition to a complete vent fluid sampling, an MBARI OsmoSampler was
deployed with a miniature temperature recorder for a year-long collection of
vent fluid in the most stable position in this very unstable vent field.
The dive finished at the east end of the vent field with the collection of
rocks bearing several high temperature sulfide minerals, suggesting that
vent fluid temperatures during the seismic event may have been much higher
than they are currently.
On Tuesday night a S-to-N tow was made 3 km west of the seamount axis; it
showed that the bulk of the hydrothermal plume above Loihi had shifted from
the WSW to the NE over the previous few days. In addition, a hydrocast was
made at Pele pit. On Wednesday night, casts were made at a site 16 km W of
Loihi, at Pele pit, at Naha vents, and at a site 4 km W of the summit.
The LONA cruise reached the end of its scientific operations on Thursday
afternoon. It was a day that started with the frustration of having our
last dive canceled due to weather -- the traditional nemesis at Loihi. A
quick decision was made to repeat the tow-yo section made on Tuesday. We
were surprised to find that the plume had shifted to nearly due north.
This shift over only a few days indicates the speed at which the Loihi
plumes can change their orientation. This last tow meant that a total of 71
km of tow-yos were conducted during the cruise, making the Loihi area one of
the most intensively studied hydrothermal systems yet.
- Frank Sansone
Chief Scientist
LOIHI SCIENCE REPORT -- Wednesday, October 9, 1996
From the scientific party on the research ship Ka'imikai o Kanaloa at
Loihi Seamount, Hawaii.
"Beyond marker 2 it's all box canyons, boulder trolls and pillar monsters." -- Terry Kerby, Sub Pilot
Tuesday's dive continued our investigation of the upper reaches of the
south rift. The dive began just west of the site of Kapo's Vents, a small
field which had been active in the late 1980s but had later stopped
venting. As on the section of the south rift explored a few days ago,
large volumes of sediment now cover much of the area; this material
consists of clay- to gravel-sized sediment. Pele's hair and flat sheets of
glass that formed as walls of large lava bubbles are common. One
interesting feature is the existance of numerous holes (approx.
5-cm diameter) at several sites in the sand layer that appear to be sites
of recently terminated venting.
An area of modest venting through a mound of small nontronite-covered
boulders was found at a depth of 1196 m. A maximum vent fluid temperature
of 17.2 deg C was measured, and a full suite of geochemical and
microbial-genetic samples was collected. It is not currently clear whether
this is part of the former Kapo's Vents or a new vent field.
Monday night's ship-based water sampling program ran two perpendicular
5-km long tow-yo sections in the vicinity of the summit. In both cases the
plume maximum was in the vicinity of Kapo's Vents. Finally, a hydrocast
was conducted in West Pit that indicated the presence of a substantial
particle plume above the pit but no associated temperature anomaly.
The weather has slowly degenerated in the past few days to fairly typical
trade wind weather for the Loihi area: 20-25 kt winds and 4-5 foot seas.
Sub deployment/recovery operations, however, continue to go very smoothly.
- Frank Sansone
Chief Scientist
LOIHI SCIENCE REPORT -- Tuesday, October 8, 1996
From the scientific party on the research ship Ka'imikai o Kanaloa at
Loihi Seamount, Hawaii.
"Vents 'R' Us...."
Monday's sub operations returned to Lohiau vents to recover a miniature
temperature recorder (MTR) that had been inserted in a vent on Friday.
The MTR showed a slow increase in temperature from 48 to 53 deg C over the
deployment, with some daily variation. It was noted that the vents which
had been sampled last week for bacterial mat with the suction sampler had
returned to their original appearance -- obviously the mat organisms grow
very rapidly!
The dive then continued upslope to explore a site covered with
nontronite-coated gravel where diffuse venting was observed at a depth of
1099 m. It is possible that this field is an early stage of the "finger
vent" type hydrothermal fields as seen previously on Loihi. The site was
given the name "Ula (red) vents".
The dive concluded on the steep western flank of the summit at a site of
previously observed intermittent venting: "Maximilian Vents" at 1249 m
depth. Plume maxima observed at this depth during our ongoing water-column
surveys led to investigation of this site. Diffuse venting was
observed coming through crusty sand that had nontronite-covered grains to
a depth of at least 5 - 10 cm.
Sunday night's ship-based water sampling program continued to home-in on
the source(s) of the large shallow (1000 - 1105 m depth) turbidity and
temperature-anomaly maxima we have been observing. The results from this
series of hydrocasts and tow-yos across the seamount suggest that a major
site of venting should be located just south of the newly formed Pele pit
near the top of the south rift. A dive to that location is being
conducted today.
- Frank Sansone
Chief Scientist
LOIHI SCIENCE REPORT -- Sunday, October 6, 1996
From the scientific party on the research ship Ka'imikai o Kanaloa at
Loihi Seamount, Hawaii.
On Saturday a sub dive to the south rift was conducted to further study
the Naha vent field discovered on Friday. The field is approximately 20 x
30 m, and is heavy covered with nontronite deposits and tan bacterial
mats. The field contains many small vents, as well as diffuse flow
through fractured pillows and large fissures. Vent fluids and proximal
plumes were sampled in detail; the highest vent fluid temperature measured
was 22.7 deg C.
Friday night's ship-based water sampling program consisted of a nearly 7
nautical mile long SW-NE tow-yo survey across the summit (the tow was run
parallel to the predominantly NE current). The hydrothermal plume was first
detected 3.5 nautical miles downstream from the summit. Unlike a similar
tow last month, a significant hydrothermal signal was observed east of the
seamount.
The first half of Saturday night's water sampling was a vertical hydrocast
located 0.75 nautical miles downstream from the summit. The purpose of
this cast was to make a detailed examination of the plume structure in the
water column. Surprisingly, the nephelometer data revealed the presence
of six major turbidity maxima over 1050 - 1330 m depth. Even more
surprising was the fact that the largest signal was at 1080 m, and that it
was associated with a significant temperature anomaly. This suggests that
there may be an as yet undiscovered major source of venting at the very
summit of Loihi (all of the vents discovered thus far are below a depth of
1180 m). Solving the riddle of where it may be should keep us very busy
in the coming days.
- Frank Sansone
Chief Scientist
LOIHI SCIENCE REPORT -- Saturday, October 5, 1996
On Friday a submersible dive up the south rift was conducted to
investigate the origin of a hydrothermal plume at 1350 m depth that was
detected during Tuesday's tow-yo survey. The dive, with Dave Clague
(Monterey Bay Aquarium Research Institute) as scientific observer, covered
a depth range of 1470 - 1250 m. A new hydrothermal vent field was found
on the rift axis at 1325 m, and was given the name "Naha vents" (from the
Hawaiian word for "cracked" or "broken"). The extensive vent field
includes many fresh fractures, including a 1-3 m wide fissure that vented
large volumes of water A smaller vent had a measured temperature of
11.2C. There is also a large number of smaller vents spread across a
nontronite-covered field. The dive concluded further up the rift at the
site of the previously active Kapo's Vents (1250 m depth); no
hydrothermal activity was observed there.
The field observations from the south rift suggest that a significant part
of the magma drainage that likely caused the summit collapses is
associated with dike injection (with associated fissure formation/
enlargement) along the south rift, rather than with surface lava flows.
Further observations, and detailed vent water sampling, will be made
during a dive today to the same site. If time allows, the dive will also
investigate areas of the rift upslope of the Kapo's Vents site.
Thursday night's ship-based water sampling program included a hydrocast>into the newly formed Pele pit. The water temperature anomalies within
the pit have greatly decreased since the August rapid response cruise
(a few tenths of a degree vs. three degrees). However, a distinct turbidity
maximum remains in the bottom waters.
- Frank Sansone
Chief Scientist
LOIHI SCIENCE REPORT -- Friday, October 4, 1996
The scientific party on the research ship Ka'imikai o Kanaloa continued
research at Loihi Seamount. On Wednesday night a tow-yo survey of nearly 10
nautical miles length was run up the western (downstream) side of the main
north-south axis of the seamount. A nephelometer graciously lent us by Dr.
Ed Baker of NOAA/PMEL (Seattle) allowed us to detect a large number of
plumes over the north half of the survey. Plumes with maxima at approx.
1350 and 1050 m were observed in addition to the large summit plume at
approx. 1150 m that we have previously observed. The presence of a
downslope plume has lead us to schedule a submersible survey today starting
at a depth of 1500 m on the south rift and heading up to the summit. Dr.
Dave Clague, until recently the scientist-in-charge at the Hawaiian Volcano
Observatory, will be the scientist on this dive.
Thursday's dive with Dr. Gary McMurtry of the University of Hawaii continued
the previous day's sampling at the Lohiau vent field on the northwest wall
of the new Pele pit. Much hotter vents were found on this dive, with
maximum vent fluid temperatures of 77C; these temperatures are much higher
than any previously measured at Loihi. In addition, a wide range of
samplers were used to collect samples for complete geochemical and
microbial-genetic analyses.
Thursday night's ship-based water sampling program included a background
hydrocast 30 miles NE of Loihi, and a hydrocast into Pele pit. Details of
the latter will be given in the next report.
- Frank Sansone
Chief Scientist
LOIHI SCIENCE REPORT -- Thursday, October 3, 1996
The research ship Ka'imikai o Kanaloa returned to Loihi Seamount on the
morning of October 2 for continuing studies of hydrothermal activity. On
the first day we 1) conducted a dive on the summit to sample hydrothermal
fluids and microbiota (see detailed description below), and 2) began a
tow-yo survey up the south ridge to look for evidence of volcanic activity
downslope of the summit (such activity would be consistent with theories
that magma chamber drainage caused the pit crater formation we have soon
on the summit). The weather conditions were ideal with only light winds
and nearly flat seas.
**********************************************************************
Pisces V dive # 310
Pilots: Terry Kerby and Allen Wright
Scientist: Frank Sansone
The dive began in the so-called "sand channel" between pre-existing East
Pit and the new Pele Pit--the bottom of the channel is actually covered
with a thick layer of fine-grained sediment. This sediment was sampled
from rocks just north of the channel with the suction sampler.
The sub then went to the new vent field on the NE wall of Pele Pit, and
began sampling at the site of the previously-deployed marker #5 (1176 m
depth). A miniature temperature recorder (MTR) was deployed, and a
maximum vent fluid temperature of over 18C was measured. We then
collected vent fluids with a titanium "majors" sampler, a titanium Lupton
gas-tight sampler, and a basket-mounted Niskin bottle that had shimmering
water exiting it when triggered. The suction sampler was also used to
collect white bacterial mat.
The sub then went to the west end of the vent field (1175 m depth), where
a large number of vents were seen; most were marked by white, streaming
mats. This area, dubbed the rubble zone, extended perhaps 50-60 m in
length and width, and was marked with several areas of recent slides and a
few relatively stable benches. Again, vent fluid samples were collected
with a "majors" sampler and a Niskin bottle, and large amounts of
bacterial mat were collected with the suction sampler. Marker #2 was left
at this site.
Finally, the sub climbed north to a fairly level gravel-covered area at a
depth of 1069 m. A small sample of the gravel (which was covered with a
thin orange coating) was collected with a partially-closed scoop sampler,
as well as several black rocks (approx. 5-cm diameter) from below the
orange layer. Some of these rocks were later found to have small glassy
areas.
************************************************************************
Cruise Participants:
Frank Sansone - Chief Scientist - University of Hawaii
Gary McMurtry - Co-Chief Scientist - University of Hawaii
C. Geoff Wheat - Co-Chief Scientist - Univ. of Alaska and Univ. of Hawaii
Craig Moyer - Michigan State University
Dave Clague - Monterey Bay Research Institute
Dave Hilton - Scripps Insitution of Oceanography
Brian Midson - University of Hawaii
Nathan Becker - University of Hawaii
Xi Yuan Wen - University of Hawaii
Max Cremer - University of Hawaii
Terri Rust - University of Hawaii
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This page created and maintained by Ken Rubin©, krubin@soest.hawaii.edu
Last page update on 27 October 1996
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