limestone. From the stratigraphic information, it was concluded that the island had
been constructed during six successive volcanic building stages (Binard et al.
1993).
Diving on The Society Hotspot
The submarine exploration of the Society hotspot using the submersibles Cyana
and Nautile started with the geological observation and sampling of the major and
most recent active volcanic edifices in 1983 and continued in 1989 and 1999.
During the 1983 and 1989 cruises, the use of Cyana permitted us to explore a
portion of the tallest and most active volcanic edifices for the first time. The first
submersible dives on the Society hotspot were done with Cyana in 1983 on the
Teahitia volcano, using the support ship N.O. Jean Charcot. The name ‘‘Teahitia’’
was given by Jean-Louis Cheminée. In Polynesian ‘‘Teahitia’’ means ‘‘standing
fire’’. The Teahitia submerged volcano (seamount) is located at 17°30
0 S148°50
0 W, about 50 km northeast of Tahiti. It is approximately 3750 m high with
a basal diameter of about 20 km. The submerged edifice culminates at a depth of
1400 m, and has three summit cones (Fig. 9.4).
In January 1989, a cruise called ‘‘Teahitia’’ took place with the submersible
Cyana and the support ship N.O. Le Suroit. The cruise was headed by Jean Louis
Cheminée and intended to explore the volcanic edifices that had shown recent
signs of activity. Because of a conflicting schedule, I could not participate on this
diving cruise, despite the fact that I had been very involved in its preparation. This
is why my PhD student, Nicolas Binard, was able to go on the cruise, and he
subsequently wrote his thesis on the morphology and style of eruption of the
volcanoes that were explored.
The targets for exploration and the priority for each of the dives were determined according to the information gathered from previous exploration and from
the earthquake monitoring in the area. Since Cyana was limited to diving to depths
of less than 3,000 m, the submersible was only able to explore the tallest of the six
major volcanic edifices of the Society hotspot: Teahitia, Turoi, Rocard, Cyana,
Moua Pihaa and the flank of Mehetia Island. The deeper ([3750 m depth) portion
of the seafloor was not accessible to Cyana. A later cruise, using the submersible
Nautile, would be necessary to reach the deepest part of the hotspot. For the first
time, the 1989 cruise with Cyana enabled us to conduct detailed observations of
the sea floor formed during hotspot volcanism. The style of volcanism, as well as
the types of rocks in correlation to their geological setting, could be defined.
Among the volcanic edifices, the Teahitia volcano is the most active on the
Society hotspot. Eruptions have taken place at the summit as well as along lateral
fissures or inside rift zones. Along the rift zones, there are a succession of small
conical vents (\200 m in height) and ‘‘hornitos’’ of silica-enriched flow overlaying bulbous pillows and tubular flows as well as sheet flows (draped and flat
flows) (Fig. 9.8a, b). The tubular flows with smooth surfaces are called ‘‘giant
316
9 Hotspots
been constructed during six successive volcanic building stages (Binard et al.
1993).
Diving on The Society Hotspot
The submarine exploration of the Society hotspot using the submersibles Cyana
and Nautile started with the geological observation and sampling of the major and
most recent active volcanic edifices in 1983 and continued in 1989 and 1999.
During the 1983 and 1989 cruises, the use of Cyana permitted us to explore a
portion of the tallest and most active volcanic edifices for the first time. The first
submersible dives on the Society hotspot were done with Cyana in 1983 on the
Teahitia volcano, using the support ship N.O. Jean Charcot. The name ‘‘Teahitia’’
was given by Jean-Louis Cheminée. In Polynesian ‘‘Teahitia’’ means ‘‘standing
fire’’. The Teahitia submerged volcano (seamount) is located at 17°30
0 S148°50
0 W, about 50 km northeast of Tahiti. It is approximately 3750 m high with
a basal diameter of about 20 km. The submerged edifice culminates at a depth of
1400 m, and has three summit cones (Fig. 9.4).
In January 1989, a cruise called ‘‘Teahitia’’ took place with the submersible
Cyana and the support ship N.O. Le Suroit. The cruise was headed by Jean Louis
Cheminée and intended to explore the volcanic edifices that had shown recent
signs of activity. Because of a conflicting schedule, I could not participate on this
diving cruise, despite the fact that I had been very involved in its preparation. This
is why my PhD student, Nicolas Binard, was able to go on the cruise, and he
subsequently wrote his thesis on the morphology and style of eruption of the
volcanoes that were explored.
The targets for exploration and the priority for each of the dives were determined according to the information gathered from previous exploration and from
the earthquake monitoring in the area. Since Cyana was limited to diving to depths
of less than 3,000 m, the submersible was only able to explore the tallest of the six
major volcanic edifices of the Society hotspot: Teahitia, Turoi, Rocard, Cyana,
Moua Pihaa and the flank of Mehetia Island. The deeper ([3750 m depth) portion
of the seafloor was not accessible to Cyana. A later cruise, using the submersible
Nautile, would be necessary to reach the deepest part of the hotspot. For the first
time, the 1989 cruise with Cyana enabled us to conduct detailed observations of
the sea floor formed during hotspot volcanism. The style of volcanism, as well as
the types of rocks in correlation to their geological setting, could be defined.
Among the volcanic edifices, the Teahitia volcano is the most active on the
Society hotspot. Eruptions have taken place at the summit as well as along lateral
fissures or inside rift zones. Along the rift zones, there are a succession of small
conical vents (\200 m in height) and ‘‘hornitos’’ of silica-enriched flow overlaying bulbous pillows and tubular flows as well as sheet flows (draped and flat
flows) (Fig. 9.8a, b). The tubular flows with smooth surfaces are called ‘‘giant
316
9 Hotspots