Colin Devey was ready on the deck on August 29, with his bag of warm clothes
and his map with the track of the dive. His dive (PN02) was planed to start at a
depth where my previous dive had stopped and then continue the ascension of the
Adams Volcano to as shallow a height as possible. At 9 AM the Nautile was ready
to dive. The pilot, Jean-Jacques Kaioun, and the co-pilot, Pierre Guyvarch, were
finishing the last checklist when the bridge communicated over the loud speaker
that they were on position above the target. The Nautile reached the bottom at
1637 m depth, and they saw sediment patches with volcanic gravel, volcanic ash
and Fe–Mn crusts similar to that observed on the previous dive (PN01). After
crossing several steps marking flow fronts, the dive ended at 942 m depth. They
collected six samples, performed two gravity stations, and deployed a water bottle
device to recover seawater. The dive lasted 5 h on the sea floor.
Thus, in order to complete the profile on the volcano by reaching the top it
would be necessary to make still another dive. This was postponed because we first
wanted to explore the other large volcano, Bounty, where we knew recent
hydrothermal activity existed on the basis of previous surface observations.
Adams seamount is morphologically similar to the Bounty, and has a summit
formed by two cones less than 100 m in height with a roughly north–south
orientation. It is during the dive made by Klass Lachschewitz with Jean-Paul
Justiniano and Frank Rosazza on September 5, that the top of the Adams Volcano
was visited. After landing at 870 m depth, they climbed up to the summit. The
summit was heavily sedimented with coral sand, volcanic ejecta, dark hyaloclastites, blocky lava flows and scoriaceous material emplaced during hydromagmatic eruptions. The sampling was successful and the divers brought up
hydrothermal iron-manganese crust, and silicic lava fragments that turned out to
be trachytes in composition. These massive looking flows are the last eruptive
event. Also, because of the shallow depth at less than 100 m, red algae, red corals,
sea urchin and white carbonate sand were observed. The fauna and the flora were
more abundant than what had been seen deeper on the flank of the edifice.
The recognition of the volcanic stratigraphy was more successful along the
Bounty Volcano during three successive dives (PN03, 04 and 14). Indeed, these
dives were made so we could obtain continuous observations of the sea floor from
2500 m to the top of the volcano at 428 meters depth, with more extensive
sampling than on the Adams volcano. Christèle Guivel, a structural geologist from
the University of Nantes, was interested in doing a dive on this site. Thus, she went
on the first (PN03) and the last (PN14) dives on the flank of the Bounty Volcano
which took place with Jean-Paul Justiniano as pilot and Frank Rosazza as a
co-pilot for the first dive, and with the pilot Jean Jaques Kaioun and Severine
Beraud as co pilot. The first dive started on August 30, at a depth of 2566 m and
ended at 1908 m. The last dive was added in order to continue the profile of dive
PN03 and join the next profile of dive PN04, which was made at shallow depths
(665 m), also on the western flank of the volcano.
Dive PN04 on August 31, was intended to identify the extent of the hydrothermal deposits on the Bounty volcano. Their existence was known but they had
never been observed in their geological context. Steve Scott, a well-known ore
334
9 Hotspots
and his map with the track of the dive. His dive (PN02) was planed to start at a
depth where my previous dive had stopped and then continue the ascension of the
Adams Volcano to as shallow a height as possible. At 9 AM the Nautile was ready
to dive. The pilot, Jean-Jacques Kaioun, and the co-pilot, Pierre Guyvarch, were
finishing the last checklist when the bridge communicated over the loud speaker
that they were on position above the target. The Nautile reached the bottom at
1637 m depth, and they saw sediment patches with volcanic gravel, volcanic ash
and Fe–Mn crusts similar to that observed on the previous dive (PN01). After
crossing several steps marking flow fronts, the dive ended at 942 m depth. They
collected six samples, performed two gravity stations, and deployed a water bottle
device to recover seawater. The dive lasted 5 h on the sea floor.
Thus, in order to complete the profile on the volcano by reaching the top it
would be necessary to make still another dive. This was postponed because we first
wanted to explore the other large volcano, Bounty, where we knew recent
hydrothermal activity existed on the basis of previous surface observations.
Adams seamount is morphologically similar to the Bounty, and has a summit
formed by two cones less than 100 m in height with a roughly north–south
orientation. It is during the dive made by Klass Lachschewitz with Jean-Paul
Justiniano and Frank Rosazza on September 5, that the top of the Adams Volcano
was visited. After landing at 870 m depth, they climbed up to the summit. The
summit was heavily sedimented with coral sand, volcanic ejecta, dark hyaloclastites, blocky lava flows and scoriaceous material emplaced during hydromagmatic eruptions. The sampling was successful and the divers brought up
hydrothermal iron-manganese crust, and silicic lava fragments that turned out to
be trachytes in composition. These massive looking flows are the last eruptive
event. Also, because of the shallow depth at less than 100 m, red algae, red corals,
sea urchin and white carbonate sand were observed. The fauna and the flora were
more abundant than what had been seen deeper on the flank of the edifice.
The recognition of the volcanic stratigraphy was more successful along the
Bounty Volcano during three successive dives (PN03, 04 and 14). Indeed, these
dives were made so we could obtain continuous observations of the sea floor from
2500 m to the top of the volcano at 428 meters depth, with more extensive
sampling than on the Adams volcano. Christèle Guivel, a structural geologist from
the University of Nantes, was interested in doing a dive on this site. Thus, she went
on the first (PN03) and the last (PN14) dives on the flank of the Bounty Volcano
which took place with Jean-Paul Justiniano as pilot and Frank Rosazza as a
co-pilot for the first dive, and with the pilot Jean Jaques Kaioun and Severine
Beraud as co pilot. The first dive started on August 30, at a depth of 2566 m and
ended at 1908 m. The last dive was added in order to continue the profile of dive
PN03 and join the next profile of dive PN04, which was made at shallow depths
(665 m), also on the western flank of the volcano.
Dive PN04 on August 31, was intended to identify the extent of the hydrothermal deposits on the Bounty volcano. Their existence was known but they had
never been observed in their geological context. Steve Scott, a well-known ore
334
9 Hotspots