From the previous surface ships’ exploration, it was found that several volcanic
and hydrothermal activities had occurred in shallow water (\1000 m depths). The
volcanic edifices chosen for diving consisted of large, collapsed calderas with
volcanic cones, which had erupted considerable amounts of pyroclasts and both
basalt and silica-enriched lava flows.
Most of the dives were made on two volcanoes called Volcano #19 and Volcano #1. These volcanoes were chosen because they were considered to be in a
dormant stage. I will describe our endeavor on volcano # 1 and suggest further
reading on Volcano #19 in a paper published by Stoffers et al. (2006).
Submersible Pisces Dives: Dive on Volcano # 1
Volcano # 1 is located at about 40 km north of Volcano # 19 and 50 km south of
the island of Tonga on the northern part of Tonga-Kermadec Ridge. Because of the
extensive fishing activities around Tonga by the local fishermen, some precautions
had to be taken during our dives. In order to prevent any accidents, the evening
before each dive, two ROV (Remote-controlled Ocean Vehicle) immersions were
done in order to have a visual observation of the sea floor along the caldera wall
and its summit (Figs. 10.2 and 10.3a, b).
A total of four dives (PIV 139, -140, -141 and -143) took place within
Volcano # 1. The objectives of the first three dives were to explore hydrothermal
venting and do a detailed study of the biological communities associated with the
thick beds of sulfur cemented ash at water depths of 160–200 m depths located
around the centrally located explosive craters on the caldera floor. A densely
populated field of mussels (200 9 400 m) covered the sea floor in a warm
hydrothermal water environment with temperatures of 30–70 °C (Stoffers et al.
2006). The highest recorded temperatures were around 130 °C. The pH of the clear
venting fluid was between 3.2 and 5.8, and there was a concentration of H 2 S and
CO 2 .
After exploring the centrally located, hydrothermally active mound of the
caldera, we wanted to explore the caldera wall in order to make a stratigraphic
geological section of the eruptive sequences contributing to the construction of
volcano #1.
Dive PIV 143 (Pisces 4, dive N°143) was also the last dive of the cruise and I
had the privilege of making this dive at about 4 km to the northwest of the
previous dive sites (Fig. 10.3a, b). On June 24, 2005, at 9:30 AM I was ready and
waiting on the deck. I was looking forward to hearing the pilot give us the go-sign.
After half an hour of waiting for the dive to take place, the pilot informed me that
we would have to postpone the dive because of a hydraulic problem. After
repairing the hydraulic leak, 2 days later, on Sunday, June 26, 2005, Terry Kerby,
Max Cremer and I were again scheduled to dive on the caldera wall. Dive PIV 143
was launched during moderately good weather conditions and lasted about 7 h
during which time geological observations and sampling were successfully carried
Cooperative Programs and Sea-Going Expeditions
355
and hydrothermal activities had occurred in shallow water (\1000 m depths). The
volcanic edifices chosen for diving consisted of large, collapsed calderas with
volcanic cones, which had erupted considerable amounts of pyroclasts and both
basalt and silica-enriched lava flows.
Most of the dives were made on two volcanoes called Volcano #19 and Volcano #1. These volcanoes were chosen because they were considered to be in a
dormant stage. I will describe our endeavor on volcano # 1 and suggest further
reading on Volcano #19 in a paper published by Stoffers et al. (2006).
Submersible Pisces Dives: Dive on Volcano # 1
Volcano # 1 is located at about 40 km north of Volcano # 19 and 50 km south of
the island of Tonga on the northern part of Tonga-Kermadec Ridge. Because of the
extensive fishing activities around Tonga by the local fishermen, some precautions
had to be taken during our dives. In order to prevent any accidents, the evening
before each dive, two ROV (Remote-controlled Ocean Vehicle) immersions were
done in order to have a visual observation of the sea floor along the caldera wall
and its summit (Figs. 10.2 and 10.3a, b).
A total of four dives (PIV 139, -140, -141 and -143) took place within
Volcano # 1. The objectives of the first three dives were to explore hydrothermal
venting and do a detailed study of the biological communities associated with the
thick beds of sulfur cemented ash at water depths of 160–200 m depths located
around the centrally located explosive craters on the caldera floor. A densely
populated field of mussels (200 9 400 m) covered the sea floor in a warm
hydrothermal water environment with temperatures of 30–70 °C (Stoffers et al.
2006). The highest recorded temperatures were around 130 °C. The pH of the clear
venting fluid was between 3.2 and 5.8, and there was a concentration of H 2 S and
CO 2 .
After exploring the centrally located, hydrothermally active mound of the
caldera, we wanted to explore the caldera wall in order to make a stratigraphic
geological section of the eruptive sequences contributing to the construction of
volcano #1.
Dive PIV 143 (Pisces 4, dive N°143) was also the last dive of the cruise and I
had the privilege of making this dive at about 4 km to the northwest of the
previous dive sites (Fig. 10.3a, b). On June 24, 2005, at 9:30 AM I was ready and
waiting on the deck. I was looking forward to hearing the pilot give us the go-sign.
After half an hour of waiting for the dive to take place, the pilot informed me that
we would have to postpone the dive because of a hydraulic problem. After
repairing the hydraulic leak, 2 days later, on Sunday, June 26, 2005, Terry Kerby,
Max Cremer and I were again scheduled to dive on the caldera wall. Dive PIV 143
was launched during moderately good weather conditions and lasted about 7 h
during which time geological observations and sampling were successfully carried
Cooperative Programs and Sea-Going Expeditions
355