exposure and the scarcity of volcanic eruptions. Dive SP03 with Eulalie Gracia,
went to the inside corner high of the western edge of the nodal basin, and showed
the presence of two basaltic units sampled at 5100–4830 m, and 4630–4300 m.
depths. These basaltic units, as was true for what we observed on the East wall
(SP 06), are thin (\200 m thick) and are intercut by serpentinized peridotite at
4800–4730 m depth. Peridotite fragments intruded by massive rodingitized gabbro
(4380 m) and partially buried by sediment are found at shallower depths
(4330–4390 m).
Unfortunately, Dive SP04, with Susanna Sichel on board, did not last long.
They were only able to remain for 1 h on the seafloor. At 4000–4286 m depths, on
the lower part of the west wall, one sample of peridotite was recovered. As soon as
the Nautile was pulled on board for repair, I decided to lower the deep-towed
camera Scampi for another station (# scampi 4) in order to have a visual observation of the West wall. The deep-towed camera observations revealed the presence of peridotite between 4100 and 3500 m depths. This confirmed the extent of
the peridotite as going all away to the top of the western wall and also revealed the
scarcity of volcanism in the area.
Dive SP05, with Gleb Udintsev as observer, was of particular interest because it
was made along the active transform fault bounding the northern part of the rift
valley. Gleb is a well-known Russian geophysicist who has made valuable international contributions to marine geology. It was a good opportunity for us to have
had him on board, so he could share his knowledge. At 75 years old, rather thin
and tall (about 6 feet tall), he was an active sea-going scientist. After this cruise, he
immediately joined a Russian ship in Antarctica for another 2 months at sea.
Dive SP05 was the first time that Gleb Udintsev had ever dived in a submersible. After all his years spent on surface ships imagining how the bottom of
the ocean must be, he was finally going to be able fulfill his dream and take a real
look at the sea floor. On December 29, 1997, at 11 h 27, Gleb was on the bottom at
4272 m depth with Max Dubois, and Olivier Cipriani. They landed on a sedimentcovered apron with exposed, fragmented lava flows. The divers went north along
the slope of the faulted terrain. Abundant staircase-like faulted blocks testified to
the extent of tectonic activity along the East–West direction of the major strikeslip motion of the St. Peter and St. Paul’s Transform fault’s northern wall. The
presence of compact sediment and conglomerates made up of broken and eroded
volcanic rocks cemented by smaller sand-size debris indicated that there had been
intense tectonic motion due to faulting. At 16 h 31, the dive ended after collecting
16 samples and spending 5 h on the sea floor. Gleb came on board, and when he
descended the ladder from the submersible, he had a big smile. The co-pilot,
Olivier, was waiting at the bottom of the staircase, with a tray carrying a glass of
vodka, a T-shirt with a picture of the Nautile and a diploma to commemorate
Gleb’s first dive.
In summary, the dives in the 25°27’W ITR axial valley at 4700 m depth have
revealed that this structure is less than 20 km long. The most recent volcanic
activity of the 25°27’W ITR was found on the eastern side of the rift valley at
4720 m within a narrow band less than 200 m wide. The geological cross-section
Diving in the Intra-Transform Ridges (ITR) of St. Peter and Paul’s Rocks
291
went to the inside corner high of the western edge of the nodal basin, and showed
the presence of two basaltic units sampled at 5100–4830 m, and 4630–4300 m.
depths. These basaltic units, as was true for what we observed on the East wall
(SP 06), are thin (\200 m thick) and are intercut by serpentinized peridotite at
4800–4730 m depth. Peridotite fragments intruded by massive rodingitized gabbro
(4380 m) and partially buried by sediment are found at shallower depths
(4330–4390 m).
Unfortunately, Dive SP04, with Susanna Sichel on board, did not last long.
They were only able to remain for 1 h on the seafloor. At 4000–4286 m depths, on
the lower part of the west wall, one sample of peridotite was recovered. As soon as
the Nautile was pulled on board for repair, I decided to lower the deep-towed
camera Scampi for another station (# scampi 4) in order to have a visual observation of the West wall. The deep-towed camera observations revealed the presence of peridotite between 4100 and 3500 m depths. This confirmed the extent of
the peridotite as going all away to the top of the western wall and also revealed the
scarcity of volcanism in the area.
Dive SP05, with Gleb Udintsev as observer, was of particular interest because it
was made along the active transform fault bounding the northern part of the rift
valley. Gleb is a well-known Russian geophysicist who has made valuable international contributions to marine geology. It was a good opportunity for us to have
had him on board, so he could share his knowledge. At 75 years old, rather thin
and tall (about 6 feet tall), he was an active sea-going scientist. After this cruise, he
immediately joined a Russian ship in Antarctica for another 2 months at sea.
Dive SP05 was the first time that Gleb Udintsev had ever dived in a submersible. After all his years spent on surface ships imagining how the bottom of
the ocean must be, he was finally going to be able fulfill his dream and take a real
look at the sea floor. On December 29, 1997, at 11 h 27, Gleb was on the bottom at
4272 m depth with Max Dubois, and Olivier Cipriani. They landed on a sedimentcovered apron with exposed, fragmented lava flows. The divers went north along
the slope of the faulted terrain. Abundant staircase-like faulted blocks testified to
the extent of tectonic activity along the East–West direction of the major strikeslip motion of the St. Peter and St. Paul’s Transform fault’s northern wall. The
presence of compact sediment and conglomerates made up of broken and eroded
volcanic rocks cemented by smaller sand-size debris indicated that there had been
intense tectonic motion due to faulting. At 16 h 31, the dive ended after collecting
16 samples and spending 5 h on the sea floor. Gleb came on board, and when he
descended the ladder from the submersible, he had a big smile. The co-pilot,
Olivier, was waiting at the bottom of the staircase, with a tray carrying a glass of
vodka, a T-shirt with a picture of the Nautile and a diploma to commemorate
Gleb’s first dive.
In summary, the dives in the 25°27’W ITR axial valley at 4700 m depth have
revealed that this structure is less than 20 km long. The most recent volcanic
activity of the 25°27’W ITR was found on the eastern side of the rift valley at
4720 m within a narrow band less than 200 m wide. The geological cross-section
Diving in the Intra-Transform Ridges (ITR) of St. Peter and Paul’s Rocks
291