175°43.58
0 W. This stratigraphic section could be completed because we made two
crossings:
(1) The first section, done on the way up the scarp of the caldera wall, was made
from the foot of the caldera near 460 m depth up to 260 m high at the summit
of the caldera. However, when reaching the ledge of the caldera wall, the dive
continued further up to explore the summit of a small volcanic cone about
400 m in basal diameter, 40 m. high, culminating at a depth of 217 m. When
reaching the summit and after sampling, we descended a gentle slope in a
south-south east direction to the edge of the caldera wall with its vertical scarp
about 259 m deep.
(2) The second section descended the steep scarp of the caldera, and took place
about 60 m away from the first one (Fig. 10.3b). Moving downward on a scarp
with a submersible is a difficult task because the pilot has to keep the submersible facing the scarp in order to have a visual contact at all time with the
sea floor. It is like backing down a mountain. This is critical and important for
the geologist who is supposed to describe the rock formations. So, the submersible descended slowly, and this was stressful for the pilot because he had
to use the vertical engine and constantly keep the submersible in neutral
buoyancy. The dexterity of the pilot was a great help for me, since it meant I
could have continuous visibility of the near vertical scarp. I was able to
observe the bedded-ash layers and pyroclastic flows that were alternated by
lava flow and intruded by dykes, just as I had seen in the previous crossing
during the upward trip on the wall. However, this second section also revealed
more intrusive and extrusive flows than what I had seen on the first crossing
(Fig. 10.3b). In addition, we observed an extensive dislocation and slumping
of the poorly consolidated pyroclastic deposits, which exposed a dyke
complex.
Before leaving the bottom, Max asked me if I wanted to take one last souvenir.
Quickly he grabbed a last sample of a loose rock fragment lying on the sedimented
sea floor. After reaching the bottom of the scarp we traveled for about 1 km along
the base of the wall until we were called from the ship and told to resurface
because the weather had started to change.
Volcanic Stratigraphy
The geological section shown in Fig. 10.4a–f was constructed according to the
in situ observations made during dive PIV 143. The section consisted of several
volcanic sequences formed of four types of volcaniclastic deposits associated with
several types of intrusive and extrusive flows (Fig. 10.4a).
Several stratigraphic sequences were identified along the wall of the caldera.
They are listed below:
Submersible Pisces Dives: Dive on Volcano # 1
357
0 W. This stratigraphic section could be completed because we made two
crossings:
(1) The first section, done on the way up the scarp of the caldera wall, was made
from the foot of the caldera near 460 m depth up to 260 m high at the summit
of the caldera. However, when reaching the ledge of the caldera wall, the dive
continued further up to explore the summit of a small volcanic cone about
400 m in basal diameter, 40 m. high, culminating at a depth of 217 m. When
reaching the summit and after sampling, we descended a gentle slope in a
south-south east direction to the edge of the caldera wall with its vertical scarp
about 259 m deep.
(2) The second section descended the steep scarp of the caldera, and took place
about 60 m away from the first one (Fig. 10.3b). Moving downward on a scarp
with a submersible is a difficult task because the pilot has to keep the submersible facing the scarp in order to have a visual contact at all time with the
sea floor. It is like backing down a mountain. This is critical and important for
the geologist who is supposed to describe the rock formations. So, the submersible descended slowly, and this was stressful for the pilot because he had
to use the vertical engine and constantly keep the submersible in neutral
buoyancy. The dexterity of the pilot was a great help for me, since it meant I
could have continuous visibility of the near vertical scarp. I was able to
observe the bedded-ash layers and pyroclastic flows that were alternated by
lava flow and intruded by dykes, just as I had seen in the previous crossing
during the upward trip on the wall. However, this second section also revealed
more intrusive and extrusive flows than what I had seen on the first crossing
(Fig. 10.3b). In addition, we observed an extensive dislocation and slumping
of the poorly consolidated pyroclastic deposits, which exposed a dyke
complex.
Before leaving the bottom, Max asked me if I wanted to take one last souvenir.
Quickly he grabbed a last sample of a loose rock fragment lying on the sedimented
sea floor. After reaching the bottom of the scarp we traveled for about 1 km along
the base of the wall until we were called from the ship and told to resurface
because the weather had started to change.
Volcanic Stratigraphy
The geological section shown in Fig. 10.4a–f was constructed according to the
in situ observations made during dive PIV 143. The section consisted of several
volcanic sequences formed of four types of volcaniclastic deposits associated with
several types of intrusive and extrusive flows (Fig. 10.4a).
Several stratigraphic sequences were identified along the wall of the caldera.
They are listed below:
Submersible Pisces Dives: Dive on Volcano # 1
357