the attractive part of being on board was the smell of a barbecue being prepared in the
kitchen where thick Texas-style sirloin steaks were served along with corn and
baked potatoes the evening before the dive. This was my favorite meal. If comfort
was primitive, the atmosphere was still extremely pleasant, friendly and relaxed with
the Alvin team and Lulu’s crew.
I was scheduled to dive in the morning at 8:00 AM (dive # 981) on the axis of
the EPR. The purpose of my dive was to monitor the fluid temperature, sample
hydrothermal fluids, and obtain rock samples. The samples were mainly to be
taken for Harmon Craig and for Chris Measure. Both men were internationally
recognized geochemists. An earlier diving exploration during the CYAMEX cruise
in 1978 had been able to define some precise hydrothermal targets. This facilitated
our reconnaissance work in finding a hydrothermal field with black smokers.
Indeed, about 15 min after the landing on the sea floor, we had already arrived on
an active hydrothermal site. This first site showed five active vents, which had
formed on a collapsed lava pond with flat slabs and sheet flow formations. We
stopped on station and started to deploy our sampling gear. The sample basket with
its compartments was in front of the porthole so it was easy to see. The first sample
had to be a hydrothermal fluid recovery, which was collected inside a titanium
bottle that Alvin’s mechanical arm held above an active chimney. This was a
difficult task for the pilot, because he had to position the submersible in a way that
it would be close enough to the orifice of the chimney where hydrothermal fluid
was spewing out at 350 °C, but not too close, since the temperature gradient was
strong enough to melt Alvin’s plastic portholes. Another site in the same general
area was sampled for fluid, which had a lower exiting temperature of 105–110 °C.
A third site was visited after having crossed a sheet flow formation associated with
several collapsed pits bordering a lava pond. At this site, two tall, skinny active
chimneys spewing out warm water were sitting on top of a pillow lava flow at the
edge of the lava pond.
For the first time, the team of geochemists found that the acid hydrothermal
solutions containing H 2 S, SO 4 plus metals and silica in suspension were exiting at
a temperature of 273–355 °C on the sea floor. The hydrothermal fluids that were
collected contained mineral compounds that had been leached from the oceanic
crust at about 0.5–3.5 km depth (See Chap. 6).
I had the opportunity to observe the volcanics formed on the seafloor of the
Pacific and compare them to what I had witnessed in the Atlantic Ocean. The
volcanic landscape looked relatively recent. It did not have the older appearance
(dusted with sediment and dull as opposed to shiny), which was commonly viewed
on the Atlantic sea floor. The lava flows were more fluidal types, forming draped
and sheet flows rather than bulbous pillows. This was an indication that the lava
had a faster rate of extrusion in this part of the World’s ocean.
The sulfide samples recovered from 21°N on the EPR were studied by Michèle
Février, my student who was working towards her PhD degree at UBO (Université
de Bretagne Occidentale, France). She was a very enthusiastic person who was
totally dedicated to her work, which concerned the hydrothermal processes
forming ore deposits. In 1981, Michèle participated on an Alvin dive with Bob
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7 Oceanic Spreading Ridges and Sea Floor Creation
kitchen where thick Texas-style sirloin steaks were served along with corn and
baked potatoes the evening before the dive. This was my favorite meal. If comfort
was primitive, the atmosphere was still extremely pleasant, friendly and relaxed with
the Alvin team and Lulu’s crew.
I was scheduled to dive in the morning at 8:00 AM (dive # 981) on the axis of
the EPR. The purpose of my dive was to monitor the fluid temperature, sample
hydrothermal fluids, and obtain rock samples. The samples were mainly to be
taken for Harmon Craig and for Chris Measure. Both men were internationally
recognized geochemists. An earlier diving exploration during the CYAMEX cruise
in 1978 had been able to define some precise hydrothermal targets. This facilitated
our reconnaissance work in finding a hydrothermal field with black smokers.
Indeed, about 15 min after the landing on the sea floor, we had already arrived on
an active hydrothermal site. This first site showed five active vents, which had
formed on a collapsed lava pond with flat slabs and sheet flow formations. We
stopped on station and started to deploy our sampling gear. The sample basket with
its compartments was in front of the porthole so it was easy to see. The first sample
had to be a hydrothermal fluid recovery, which was collected inside a titanium
bottle that Alvin’s mechanical arm held above an active chimney. This was a
difficult task for the pilot, because he had to position the submersible in a way that
it would be close enough to the orifice of the chimney where hydrothermal fluid
was spewing out at 350 °C, but not too close, since the temperature gradient was
strong enough to melt Alvin’s plastic portholes. Another site in the same general
area was sampled for fluid, which had a lower exiting temperature of 105–110 °C.
A third site was visited after having crossed a sheet flow formation associated with
several collapsed pits bordering a lava pond. At this site, two tall, skinny active
chimneys spewing out warm water were sitting on top of a pillow lava flow at the
edge of the lava pond.
For the first time, the team of geochemists found that the acid hydrothermal
solutions containing H 2 S, SO 4 plus metals and silica in suspension were exiting at
a temperature of 273–355 °C on the sea floor. The hydrothermal fluids that were
collected contained mineral compounds that had been leached from the oceanic
crust at about 0.5–3.5 km depth (See Chap. 6).
I had the opportunity to observe the volcanics formed on the seafloor of the
Pacific and compare them to what I had witnessed in the Atlantic Ocean. The
volcanic landscape looked relatively recent. It did not have the older appearance
(dusted with sediment and dull as opposed to shiny), which was commonly viewed
on the Atlantic sea floor. The lava flows were more fluidal types, forming draped
and sheet flows rather than bulbous pillows. This was an indication that the lava
had a faster rate of extrusion in this part of the World’s ocean.
The sulfide samples recovered from 21°N on the EPR were studied by Michèle
Février, my student who was working towards her PhD degree at UBO (Université
de Bretagne Occidentale, France). She was a very enthusiastic person who was
totally dedicated to her work, which concerned the hydrothermal processes
forming ore deposits. In 1981, Michèle participated on an Alvin dive with Bob
202
7 Oceanic Spreading Ridges and Sea Floor Creation