By now, the hydraulic leak had become serious because Niva turned towards
me and said that we must leave the bottom at soon as possible. Then he took the
phone and called the surface to ask permission to come up. It was 17h30 when
Niva tried to switch the button on the control panel on the port side. Suddenly a red
light flashed and the electro–magnetic device that releases the iron pellets from its
container did not open. In order for Cyana to come up, it was necessary to ‘‘drop
some of its weight’’ by releasing the iron pellets it carried. Because of the
hydraulic leak in the system, we could not use the ‘‘electrically commanded valve
release’’. Normand, the co-pilot sitting behind us, tried to release the weight with
an emergency hand-manipulator, but that did not work either. The manual emergency device was stuck, so it did not move at all. There we were, sitting on the
domed-shaped volcanic cone where I was trying to keep cool and continue my
description as well as take some pictures of the same outcrop at different angles,
while the submersible Cyana was slightly moving and turning by inertia. In the
meantime, both the pilot and co-pilot were trying to switch on several devices as
well as using the emergency handle for releasing the weights. In such a case,
several options are possible for releasing weight and making the Cyana lighter.
One is the release of the mechanical arm and eventually the rack with our collected
samples. This would have been disastrous because we would have lost all our dive
data.
Eventually, the weight pellets were finally released so we could float back up to
the surface. We usually have a tendency to try and forget about any dangers that
we have experienced on the bottom once we are back on board. These are the kind
of events that are not discussed, except for the need of making any technical
repairs.
Two years later in 1984, during the Geocyarise cruise, another dive was
scheduled to take place on the same off-axis volcano, called the Clipperton Seamount. The purpose was to verify if any changes had occurred on the summit of
the volcano. This time the best person to explore this type of edifice was Vladimir
Nesteroff, a marine geologist specialized in sediment transport generated from
volcanic edifices and from the slumping of continental margins. Vladimir’s dive
was programmed with George Arnoux, the pilot, and J-M. Nivaggioli, co-pilot, to
explore the top of the seamount. The objective was to study the volcanic structure
and its landscape. It was found that the summit of the seamount represented a
collapsed crater with its western wall still intact rising 100 m from the summit. It
was in this crater that we had observed the tumulus feature described in the
previous dive. A concluding observation was that the collapsed nature of the crater
is due to the retrieval of magma during eruption without the magma chamber being
replenished.
The off-axis Western seamount, also found during the Clipperton cruise of
1981, is another off-axis volcano 670 m high above the surrounding sea floor and
located at less than 6 km from the adjacent ridge axis at 11°30
0 n and 103°50
0 W
(Fig. 7.22). In addition to having scoria-like flows (resembling ‘‘aa’’ in subaerial
volcanism) and sheet flows, the Western seamount is characterized by hydrothermal Fe–SI oxyhydroxide edifices (Fig. 7.25a) and hyaloclastite slabs. Recent
Off-Axial Seamounts on the EPR at 12°50
0 N and 11°20
0 N
231
me and said that we must leave the bottom at soon as possible. Then he took the
phone and called the surface to ask permission to come up. It was 17h30 when
Niva tried to switch the button on the control panel on the port side. Suddenly a red
light flashed and the electro–magnetic device that releases the iron pellets from its
container did not open. In order for Cyana to come up, it was necessary to ‘‘drop
some of its weight’’ by releasing the iron pellets it carried. Because of the
hydraulic leak in the system, we could not use the ‘‘electrically commanded valve
release’’. Normand, the co-pilot sitting behind us, tried to release the weight with
an emergency hand-manipulator, but that did not work either. The manual emergency device was stuck, so it did not move at all. There we were, sitting on the
domed-shaped volcanic cone where I was trying to keep cool and continue my
description as well as take some pictures of the same outcrop at different angles,
while the submersible Cyana was slightly moving and turning by inertia. In the
meantime, both the pilot and co-pilot were trying to switch on several devices as
well as using the emergency handle for releasing the weights. In such a case,
several options are possible for releasing weight and making the Cyana lighter.
One is the release of the mechanical arm and eventually the rack with our collected
samples. This would have been disastrous because we would have lost all our dive
data.
Eventually, the weight pellets were finally released so we could float back up to
the surface. We usually have a tendency to try and forget about any dangers that
we have experienced on the bottom once we are back on board. These are the kind
of events that are not discussed, except for the need of making any technical
repairs.
Two years later in 1984, during the Geocyarise cruise, another dive was
scheduled to take place on the same off-axis volcano, called the Clipperton Seamount. The purpose was to verify if any changes had occurred on the summit of
the volcano. This time the best person to explore this type of edifice was Vladimir
Nesteroff, a marine geologist specialized in sediment transport generated from
volcanic edifices and from the slumping of continental margins. Vladimir’s dive
was programmed with George Arnoux, the pilot, and J-M. Nivaggioli, co-pilot, to
explore the top of the seamount. The objective was to study the volcanic structure
and its landscape. It was found that the summit of the seamount represented a
collapsed crater with its western wall still intact rising 100 m from the summit. It
was in this crater that we had observed the tumulus feature described in the
previous dive. A concluding observation was that the collapsed nature of the crater
is due to the retrieval of magma during eruption without the magma chamber being
replenished.
The off-axis Western seamount, also found during the Clipperton cruise of
1981, is another off-axis volcano 670 m high above the surrounding sea floor and
located at less than 6 km from the adjacent ridge axis at 11°30
0 n and 103°50
0 W
(Fig. 7.22). In addition to having scoria-like flows (resembling ‘‘aa’’ in subaerial
volcanism) and sheet flows, the Western seamount is characterized by hydrothermal Fe–SI oxyhydroxide edifices (Fig. 7.25a) and hyaloclastite slabs. Recent
Off-Axial Seamounts on the EPR at 12°50
0 N and 11°20
0 N
231