Nadir’s main deck. Max had been on other diving cruises with me; before he
became a pilot he had also been working on the navigation team to deploy the
transponders and the positioning systems for the submersible. Max was a goodlooking young man with blond hair and a mustache. He was very much appreciated by some of the female scientists. He was a pleasant and experienced person,
so I was pleased to do our Christmas Day dive with him.
At 11h54 we reached a sedimented bottom with partially buried collapsed
pillow lava. The sediment contained traces of bio-perturbations and traces of
holothurians. To the east, we saw an echo on our radar, probably a rocky outcrop.
We decided to go to see what it was. I wanted to find out where the most recent
volcanic or tectonic activity occurred, in order to know the state of evolution of the
spreading axis.
At 12h12 we arrived at what seemed to be the foot of the East wall of the rift
valley. We had to go along the strike of the scarp along several talus piles and
make sure that we were on the first scarp of the wall. Then, after taking the first
sample at 4670 m depth, we changed our course to a Northeast direction (310°)
and went towards the center of the rift valley to try to find the area with the most
recent eruptions. At 13h31, we were on a 2 m wide fissure cutting through a
relatively fresh glassy lobated flow. I was happy to see that the sediment cover had
decreased and that the fissure was recently formed. This suggested to me that we
were on a tectonically active axis of the rift valley and that by taking a bearing
along the same strike as the fissure, we might be able to follow the axis of the rift
in order to get to where the spreading is currently taking place.
Hence, after taking a sample, we moved by zigzagging to N 300°. Indeed our
approach turned out to pay off because we encountered several ‘‘en echelon’’
fissures oriented in a 340° direction. The current on the sea floor deviated our
course more to the west. The fissures exposed lobated flows with glassy chilled
margins. The presence of the sediment cover along our dive track was due to the
fact this region of the Equatorial Atlantic has a large amount of plankton production. Indeed, through the porthole we could see white spots of dead foraminifera dropping down on the sea floor. The result of this dive was very conclusive
because we found that this small ITR segment is still spreading, as was evidenced
by the abundance of the 3–5 m fissures rather than by traces of recent volcanism.
Now the next step was to define how much volcanic activity had occurred in the
past. In order to delineate the continuity and extent of volcanism over time, it is
important to go to the sides of the rift valley to see if the same volcanic events took
place in the past. Hence the goal of the next dive would be to climb the East wall
of the ITR.
The next morning dive SP02 with Thierry Juteau, Patrick Ceilan as pilot and
Patrice Lubin as co-pilot took place. They landed at the foot of ITR’s East wall at
4700 m and followed an easterly course along the slope up to a depth of 3868 m,
which they reached after 4 h and 58 min. At the beginning of the dives, Thierry
noticed the presence of fresh flows at the intersection of the East wall and the Rift
valley floor at 4700 m. At least two successive lobated flows were recognized,
with the youngest flow being darker and shinier. He described a ‘‘glowing’’ of the
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8 Fracture Zones and Transform Faults
became a pilot he had also been working on the navigation team to deploy the
transponders and the positioning systems for the submersible. Max was a goodlooking young man with blond hair and a mustache. He was very much appreciated by some of the female scientists. He was a pleasant and experienced person,
so I was pleased to do our Christmas Day dive with him.
At 11h54 we reached a sedimented bottom with partially buried collapsed
pillow lava. The sediment contained traces of bio-perturbations and traces of
holothurians. To the east, we saw an echo on our radar, probably a rocky outcrop.
We decided to go to see what it was. I wanted to find out where the most recent
volcanic or tectonic activity occurred, in order to know the state of evolution of the
spreading axis.
At 12h12 we arrived at what seemed to be the foot of the East wall of the rift
valley. We had to go along the strike of the scarp along several talus piles and
make sure that we were on the first scarp of the wall. Then, after taking the first
sample at 4670 m depth, we changed our course to a Northeast direction (310°)
and went towards the center of the rift valley to try to find the area with the most
recent eruptions. At 13h31, we were on a 2 m wide fissure cutting through a
relatively fresh glassy lobated flow. I was happy to see that the sediment cover had
decreased and that the fissure was recently formed. This suggested to me that we
were on a tectonically active axis of the rift valley and that by taking a bearing
along the same strike as the fissure, we might be able to follow the axis of the rift
in order to get to where the spreading is currently taking place.
Hence, after taking a sample, we moved by zigzagging to N 300°. Indeed our
approach turned out to pay off because we encountered several ‘‘en echelon’’
fissures oriented in a 340° direction. The current on the sea floor deviated our
course more to the west. The fissures exposed lobated flows with glassy chilled
margins. The presence of the sediment cover along our dive track was due to the
fact this region of the Equatorial Atlantic has a large amount of plankton production. Indeed, through the porthole we could see white spots of dead foraminifera dropping down on the sea floor. The result of this dive was very conclusive
because we found that this small ITR segment is still spreading, as was evidenced
by the abundance of the 3–5 m fissures rather than by traces of recent volcanism.
Now the next step was to define how much volcanic activity had occurred in the
past. In order to delineate the continuity and extent of volcanism over time, it is
important to go to the sides of the rift valley to see if the same volcanic events took
place in the past. Hence the goal of the next dive would be to climb the East wall
of the ITR.
The next morning dive SP02 with Thierry Juteau, Patrick Ceilan as pilot and
Patrice Lubin as co-pilot took place. They landed at the foot of ITR’s East wall at
4700 m and followed an easterly course along the slope up to a depth of 3868 m,
which they reached after 4 h and 58 min. At the beginning of the dives, Thierry
noticed the presence of fresh flows at the intersection of the East wall and the Rift
valley floor at 4700 m. At least two successive lobated flows were recognized,
with the youngest flow being darker and shinier. He described a ‘‘glowing’’ of the
288
8 Fracture Zones and Transform Faults