update is provided by Dave
was a quiet day on the ship as we transited from Guaymas Basin to the
northernmost segment of the East Pacific Rise, due east of Cabo San Lucas.
The transit will take us about 30 hours, and we will arrive later tonight
in plenty of time to dive tomorrow at 6:30 in the morning. This segment of
the East Pacific Rise, named the Alarcon Rise, will be our work area for
the next two dives as we search for hydrothermal vents in the region. But
I have gotten ahead of myself. The quiet
day was used by most of the scientific party to catch up on samples in the
lab, add to notes on samples and observations from the previous dives, do
some laundry, read a book, get some exercise, even to try one’s luck at
fishing off the stern of the R/V
Western Flyer. At right, Joe
and Darrell look on as Erik
reels in a small yellowtail tuna. I
suspect there will be more than one person with sunburn tonight, despite
the cloudy day!
few years ago, a plume of water emitted from hydrothermal vents was
detected above the Alarcon Rise during a cruise led by Dr. Peter Lonsdale
at Scripps Institution of Oceanography.
During their cruise, they did not locate the vents that were emitting that
plume of hydrothermal water since they did not have an ROV or submersible.
Armed with a bathymetric map of the region and the location where Lonsdale
found the plume, which he generously provided to us, we are now going to
see if we can locate the actual hydrothermal vents and sample the animals
that live there. This requires a bit of wishful thinking: that the vents
are still active today, that the plume was located close enough to the
vents to serve as an exploration guide, and that the vents will be large
enough for us to have a reasonable chance to locate them.
seems like it should be fairly simple, but the location where the plume
was detected can be some distance from the actual vents as the hot water
rises and then spreads out, only to be carried by unknown currents in
unknown directions. In addition, the location where the plume was located
is not that precise, since the plume was detected by a sensor towed behind
a ship. It also makes it more challenging in that the ROV cameras can only
“see” a short distance (15 meters or so, if the water is very clear)
on the bottom, and the possible area is large. It is quite possible to
drive by in the dark and miss the feature one is searching for.
increase our chance of success, we have also considered where other
hydrothermal vents are located on the ridge system. We have examined the
bathymetry and tried to locate the axis of spreading on the ridge axis
(the place where the latest lava flows should have erupted), and we have
determined the region along the ridge axis where the ridge erupts most
frequently, which is the shallowest point along the axis. It turns out
that the plume is located within a few hundred meters of the ridge axis,
but several kilometers north of the shallowest, most volcanically active
part of the ridge. For these reasons, we have planned our initial survey
to move to the south, back and forth across the axis of the ridge, working
towards the shallowest section of the ridge axis. We will also look for
increased animal populations that commonly surround the actual
hydrothermal vent communities and for the presence of hydrothermal
sediments. Using these types of clues, we hope to locate the vents on the
During this preliminary search, I will also be able to get a good look at the volcanic terrain along the ridge axis, sample some of the lava flows for later analysis, and attempt to determine the style of eruptions that have occurred in the region and shaped the ridge axis. One of my main interests is in determining if eruptions along the East Pacific Rise have a mildly explosive character, as we have found at the Gorda Ridge off northern California. To determine this, I will try to collect fine, glassy particles that settle out of the water from such eruptions. Many of these particles are delicate, thin, bubble-wall fragments that form when large bubbles of gas escape through the surface of the magma at the erupting vent. I will try to collect these small, sand-sized particles in sediments using short cores or to vacuum them directly from the surfaces of lava flows using a small suction sampler designed for this task. If our plan is sound and we are lucky, I will collect the samples I need to test the idea that eruptions along mid-ocean ridges are significantly more violent than usually thought, and we will have located the hydrothermal vents and their animals communities for sampling on the next dive and perhaps on the last dive at the end of the cruise.