How magma flows from the Earth’s mantle to the surface is poorly understood.
This project will focus on
magma interaction between the Galapagos mantle plume and mid-ocean ridge. It will include three key components: (1) New
marine resistivity imaging using magnetotelluric (MT) sounding to image melt distribution; (2) Geochemical
analysis of existing and new dredge samples along the northern Galapagos lineaments and Western Galapagos
Spreading Center; and (3) Geodynamical modeling of two-phase melt channelization to constrain the physical
viability of melt localization.
These data will help us determine if melt flows slowly through
pore spaces between mantle minerals, or quickly through melt-rich channels. This will help in understanding
where seafloor volcanoes form and how frequently they erupt, and will significantly improve the understanding of melt transport in
the asthenosphere
and melt localization processes. These results will be integrated to generate a new global model
for plume-ridge interaction and asthenospheric melt transport in general.
Funded by the US National Science Foundation (OCE 2334541/42) and UK-NERC, with collaboration from the Charles Darwin Foundation
in Galapagos.
Here is a map showing the planned locations of MT soundings and dredge sites across the volcanic ridges that appear to connect the Galapagos plume with the nearby mid-ocean ridge:
Apologies, dear reader, for the radio silence over the last few days. Tuesday was not a great day for me. I got up early to
start recovering and re-deploying the MT instruments at first light, and discovered that the acoustic systems we use to survey and release
the instruments were extremely noisy. We swapped cables, tried different hull transducers, tried putting our "dunking" transducer into the water over the
side of the ship, but nothing worked. We figured out that the seafloor instruments could hear us, but we could not hear their replies.
This made locating the instruments by triangulation impossible, but worse still we would have to send a release command and wait for a couple
of hours to see if the instrument did indeed release and reach the surface. This is not efficient, and quite nerve-racking. Tushar had been playing with a
hydrophone attached to the ship's hull, and saw that there was a narrow band of 12 kHz acoustic noise being generated by the ship.
We tried switching off everything we could but it wouldn't go away. Other things started breaking: a recovery float flooded with water on
one instrument, and a cable we used to test acoustics on deck broke. I was at wit's end when we discovered that putting the dunking ducer
over the port side, instead of the starboard side, of the ship allowed us to talk to the instruments. Whatever was making the noise must
be on the starboard side of the vessel. Using a dunking ducer means stopping the ship to
send release commands, instead of using the ship's hull trandsucer while we are in motion, but that's a small price to pay to keep control
over what is going on. We are now a little over a third of the way through the turnarounds and things are going much better today
(Wednesday).
I tried for another green flash photo (see the Tehuantepec and
Gulf of Mexico blogs), which didn't quite work but
the clouds are pretty, a bit like a Galapagos tortoise:
11-12 October 2026.
Three days of dredging, as promised. I have learned that there is "active dredging" and "passive dredging". In passive
dredging many hundreds of meters of dredge cable are laid out on the seafloor, the ship parks in DP (dynamic positioning), and the cable is slowly
hauled in, dragging the cable and dredge bucket across the seafloor. Active dredging, preferred by our group, involves putting
only a hundred or so meters of cable on the seafloor, guided by the seafloor reflection from the 12 kHz pinger, and
then driving the ship slowly at 0.5 knots to drag the dredge bucket. The tension on the cable tells you if you have caught something:
Current time is to the left, so you see tension building over several minutes and then dropping abruptly as you break off a chunk of
rock, or break the dredge bucket loose from what it is caught up on. The former is preferred. The working load of the cable is 20,000 lbs in
this case. The ship and cable are protected by shear pins designed to break the dredge loose if this tension is reached. This isn't great,
as you lose the rocks and perhaps the dredge bucket, so if you get close to 20,000 lbs you pay out cable to decrease the tension and back the ship
over the cable to make the angle more vertical and break things loose. This happened on one of the last dredges, and indeed the
size and quantity of the rocks reflected the high tensions observed:
Left: A big bucket of rocks. Right: People admiring a big box of big rocks. Tushar, proud dredgemeister, in the foreground.
Darwin Island through the Atlantis' A-frame during a dredge. The two little pinnacles to the right were once an arch ("Darwin's Arch") that
collapsed in 2021.
10 October 2026.
As expected, we finished deploying the MT instruments just before midnight. I estimated that it would
take 2 days to deploy the 45 instruments, and we beat the estimate by 3 minutes. While the ship prepared
for 3 days of dredging ops, the MT crew took a break to play the marine EM lab's favorite game,
Bang!
Then it was back to work, dredging for the samples that would provide geochemical constraints on where
mantle melt came from and its volatile (water and CO2) content. Pictures: Left - the 12 kHz acoustic pinger that is
used to tell when the dredge bucket is on the seafloor. Center - the dredge bucket leaving the water.
Right - shaking rocks from the dredge.
When the pallet of rocks makes it back to the waiting scientists, a feeding frenzy sets in. Did we bring
any biology back (into the ethanol with you!)? Is there any volcanic glass (favored by the geochemists)?
Any cool shaped samples? Etc...
A lovely evening for more dredging:
9 October 2026.
As of this evening we have almost finished deploying the MT instruments. We have had a few
bits and pieces to repair, but things are going really well. Apart from a few rain squalls, the
weather has been exceptionally nice. Hardly a white-cap to be seen and the swell is barely noticeable.
The sun is hot during the day but the air temperature, pretty well right on the equator, is most
pleasant (unlike San Diego, which I am told is still baking). This evening was almost cool and had
a rather nice sunset:
We will finish deployments before midnight, and then start dredging for rock samples. More on that later.
8 October 2026.
As anticipated, we started deploying instruments at 11 pm, right at our shift change (the EM lab
works two 12-hour shifts, noon to midnight and midnight to noon). This is the first deployment of
this project:
This evening we have half the instruments deployed. We have 45 instruments and the plan is
to do 90 sites, deploying odd-numbered sites first, taking a break to do some dredging, and then moving
the instruments to the even numbered sites.
Jake isn't able to make this cruise because of other commitments. Two of my ex-students, David and Karen,
have graciously agreed to come along to help me out. They both have lots of experience with my instrument
systems. Chris is leading the midnight shift and Karen is leading the noon shift. Karen's shift have called
themselves JAKE:
Josephine, Aitano, Karen, Eliana.
(This is only a small stretch - Gaetano's name is Aitano in the dialect of the Italian village
he hails from.)
7 October 2026.
This morning we arrived in the Galapagos, at Puerto Ayora on Isla Santa Cruz. Immigration officers boarded
the vessel and we all lined up to get visas stamped in our passport. It was a jolly affair as these things
go, and at the end they all sang happy birthday to one of the officers who, presumably, had a birthday
that day.
After immigration left, the rest of the science party (Mark and Kan) as well as observers and
scientists from the Charles Darwin Foundation, the Galapagos National Park, and the Ecuadorian Navy, arrived
by water taxi. Here's the taxi arriving at the Atlantis with Puerto Ayora in the background:
To board the ship you have to climb the pilot's ladder, which can be a tricky business. Fortunately
the weather is very good (and hopefully will remain so):
We are now heading for the first MT site and will start deploying instruments around mid-night.
5 October 2026.
Yesterday we set sail after breakfast and we started to set up the lab and settle in - it is nice to
have a few days transit before we start work. The deck is fully loaded with instruments:
I was hoping that we could sneak some SUESI tows into this project, which is only funded for MT work and
dredging, but SUESI, my deep-towed EM transmitter, needs to be deployed through the ship's A-frame. I was
told that I wouldn't be able to use the Atlantis' A-frame and now I know why- it is dedicated
to deploying Alvin, the deep ocean submarine, and there's not much room for anything else.
Today's big job is installing electrodes and cables into the
arms of the MT instruments.
This is my least favorite part of the operation, so I am happy that we have lots of students aboard to help with
this. 45 instruments with 4 arms each is a lot of arms (I leave the arithmetic to you), but it has to be
done carefully and properly. A bad connection on an electrode and we lose the entire MT site.
My last trip was notable for the boobies that hung around the ship
(web page) and it didn't take long
for them to show up for this cruise (photo courtesy Kyle).
3 October 2026.
We're here! Back in Panama (for some of us) after a fairly miserable air travel experience (a little fog in San Diego turned our two-leg trip into a four-leg trip with an
overnight in Miami). Fortunately we had built a buffer day into our travel plans, based on similar past experiences. Our ship, the R.V. Atlantis, had loaded our equipment in Norfolk, Virginia,
a couple of weeks ago and passed through the Panama Canal Thursday night, stopping at anchor on the Pacific side. This morning we left the hotel to get a
water taxi out to the ship, and after convincing the fellow at the port gate to let us through (took a couple of attempts) we donned life jackets for the ride out.
We are looking forward to weighing anchor tomorrow morning and getting on our way.
