permitted, to take an additional water sample on a low temperature white smoker
that had already been discovered on the previous dives. Francis described the site
with four chimneys in the most detail: three black and one white smoker. On the
east side, a small chimney looking like a ‘‘Chinese hat’’ also occurred at the foot of
the main edifice.
The main edifice is about 10 m in diameter located on the western edge of the
lava pond along a fault scarp oriented at 340° corresponding roughly to the
direction of the spreading axis. An animal community made up of Galathea crabs,
dandelions and vent fish were seen. When going further northwest towards the
western wall, the terrain became older and the sediment dusting on top of the lava
flow increased. A field of at least three dead chimneys 2.5 m tall was observed at
less than 50 m from the previous active black smoker site. This field was accidentally found while going back to the ‘‘lift’’ in order to pick-up the fluid bottles.
After each sampling, the submersible had to go back to the ‘‘lift’’ in order to put
the full bottle back into the storage rack. At the end of a day’s sampling, the ‘‘lift’’
was released from its weight and rose to the surface where it was located and
recovered by the ship’s crew.
At 16:05, at a depth of 2,608 m, pilot Guy Sciarrone activated the vertical
propeller and took Cyana above the black plume of the hydrothermal fluid, which
was being diluted in the seawater. The temperature at the edge of the plume, as
registered by the outside sensors, was about 3.8 °C which is more than the twice
the temperature of the ambient seawater. Above about 25 m over the hydrothermal
chimney, the black smoker fluid had decreased in intensity and was almost totally
diluted in the seawater. The dive ended at 16h15, above the hydrothermal plume.
Guy Sciarrone is a reserved man who is a very conscientious engineer and an
experienced pilot. When at sea, he spent most of his time taking care of the
submersible as if it were his ‘‘baby’’. He showed his concern during and after each
dive, being worried that the submarine might come back damaged after its voyage
to the bottom.
It was after dive Cy82-19 on the EPR ‘‘Chain site’’ hydrothermal field that Guy
Sciarone came to me because he was concerned. He told me:
Roger, I had difficulty recognizing the site this time. I am worried that we might have
missed the previous vent and that we may have sampled the wrong one.’’ He added: ‘‘I am
really puzzled, how can it be possible that the aspect of the site has changed so much since
the last time we saw it, which was on dive Cy82-16, only 4 days ago?
This was a serious piece of information. Geologists are used to observing longterm changes on the order of hundreds or thousands of years. A change of geological form in a time lapse of just a few days seemed highly unexpected. However, then some doubts came to my mind. If what Guy said was true, and if it were
really possible for a site to change its appearance in only a few days, then we could
be dealing with a time span that is closer to the time span on a human scale. Could
this be possible?
I knew Guy was an experienced pilot and a thorough navigator, so he could not
have made a mistake. If he questioned his ability to recognize the site, this meant
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7 Oceanic Spreading Ridges and Sea Floor Creation
that had already been discovered on the previous dives. Francis described the site
with four chimneys in the most detail: three black and one white smoker. On the
east side, a small chimney looking like a ‘‘Chinese hat’’ also occurred at the foot of
the main edifice.
The main edifice is about 10 m in diameter located on the western edge of the
lava pond along a fault scarp oriented at 340° corresponding roughly to the
direction of the spreading axis. An animal community made up of Galathea crabs,
dandelions and vent fish were seen. When going further northwest towards the
western wall, the terrain became older and the sediment dusting on top of the lava
flow increased. A field of at least three dead chimneys 2.5 m tall was observed at
less than 50 m from the previous active black smoker site. This field was accidentally found while going back to the ‘‘lift’’ in order to pick-up the fluid bottles.
After each sampling, the submersible had to go back to the ‘‘lift’’ in order to put
the full bottle back into the storage rack. At the end of a day’s sampling, the ‘‘lift’’
was released from its weight and rose to the surface where it was located and
recovered by the ship’s crew.
At 16:05, at a depth of 2,608 m, pilot Guy Sciarrone activated the vertical
propeller and took Cyana above the black plume of the hydrothermal fluid, which
was being diluted in the seawater. The temperature at the edge of the plume, as
registered by the outside sensors, was about 3.8 °C which is more than the twice
the temperature of the ambient seawater. Above about 25 m over the hydrothermal
chimney, the black smoker fluid had decreased in intensity and was almost totally
diluted in the seawater. The dive ended at 16h15, above the hydrothermal plume.
Guy Sciarrone is a reserved man who is a very conscientious engineer and an
experienced pilot. When at sea, he spent most of his time taking care of the
submersible as if it were his ‘‘baby’’. He showed his concern during and after each
dive, being worried that the submarine might come back damaged after its voyage
to the bottom.
It was after dive Cy82-19 on the EPR ‘‘Chain site’’ hydrothermal field that Guy
Sciarone came to me because he was concerned. He told me:
Roger, I had difficulty recognizing the site this time. I am worried that we might have
missed the previous vent and that we may have sampled the wrong one.’’ He added: ‘‘I am
really puzzled, how can it be possible that the aspect of the site has changed so much since
the last time we saw it, which was on dive Cy82-16, only 4 days ago?
This was a serious piece of information. Geologists are used to observing longterm changes on the order of hundreds or thousands of years. A change of geological form in a time lapse of just a few days seemed highly unexpected. However, then some doubts came to my mind. If what Guy said was true, and if it were
really possible for a site to change its appearance in only a few days, then we could
be dealing with a time span that is closer to the time span on a human scale. Could
this be possible?
I knew Guy was an experienced pilot and a thorough navigator, so he could not
have made a mistake. If he questioned his ability to recognize the site, this meant
218
7 Oceanic Spreading Ridges and Sea Floor Creation