Volcanoes, represents a relic of an ancient pre-hotspot edifice located on the
northwestern corner of the Society hotspot (Figs. 9.3, 9.4). Their seismicity is due to
crustal fracturing reactivated during hotspot activity.
All the large hotspot volcanoes show parasite cones and radial volcanic ridges
or steep-sloped aprons. The aprons represent radial fissures of magma channels,
often ending in small volcanic cones along the flanks of the edifices. The sea floor
at a distance from the base of the major volcanic edifices is relatively flat and
covered with fresh volcanic glass debris mixed with a thin sediment cover.
A compilation of the multichannel bathymetric data (Bonneville personal communication; Jordahl et al. 2004; Cheminée et al. 1988; Stoffers et al. 1989) shows
that the hotspot volcanoes are surrounded by topographic lows (3600–3950 m
depth) bordered by deeper ([4000 m depth) abyssal hill regions representing an
ancient, 65 million year-old oceanic crust.
When assuming that the plate moves at a speed of 11 cm/yr over a fixed hotspot
(Heron 1972; Duncan et al. 1974; Minster and Jordan 1978), volcanic activities
within the hotspot must have taken place during the last 900,000 years. Also,
potassium-argon isotopic age dating carried out by Isabelle Le Roy in 1994
indicates that most submarine edifices are recent and go up in age to 550,000 years
old. The youngest island of the chain is Mehetia, whose last eruption took place
about 25000–73000 years ago (Leroy 1994).
Mehetia Island
The island formerly called ‘‘Meetia’’ or Mehetia lies 60 miles away from Tahiti
and is part of the Society volcanic chain. Captain Samuel Wallis first discovered
the Island on June 17, 1767. The island is now privately owned and is uninhabited
except for the presence of a few goats. Mehetia (2 km
2 ) is a volcanic cone and
rises 435 meters above the sea surface. It is about 4035 m high above the sea floor
of the Society hotspot (Fig. 9.4). The last volcanic eruption on the island was dated
as being 1 million years ago. During the last subaerial explosive eruption, a crater
150 m in diameter and 80 m deep was built. The only evidence of recent volcanism is found on the south flank of the volcano, at more than 1600 m depth, where
seismic activity was detected (Réseau Sismique Polynésien, RSP) from December
to April 1981. This was a target area for the submersible Cyana’s dive TH10 that
took place in 1989. Dive TH10 found evidence of recent underwater explosive
eruptions in the form of pyroclastic flows at 2301 m depth. The eruption took
place from a small parasite cone located on the southern flank of the island at
2300–2400 m depths (Figs. 9.5, 9.6).
This uninhabited island has vertical, volcanic cliffs, which makes the island
difficult to access. During the FS SONNE cruise of 1987, a group of German and
French scientists landed on the SW side to sample the island. Because of the strong
wave action on the rocky coast, the approach to the island was dangerous.
A zodiac was first sent with the ship’s captain, Hartmut Andresen, to explore the
The Society Hotspot
313
northwestern corner of the Society hotspot (Figs. 9.3, 9.4). Their seismicity is due to
crustal fracturing reactivated during hotspot activity.
All the large hotspot volcanoes show parasite cones and radial volcanic ridges
or steep-sloped aprons. The aprons represent radial fissures of magma channels,
often ending in small volcanic cones along the flanks of the edifices. The sea floor
at a distance from the base of the major volcanic edifices is relatively flat and
covered with fresh volcanic glass debris mixed with a thin sediment cover.
A compilation of the multichannel bathymetric data (Bonneville personal communication; Jordahl et al. 2004; Cheminée et al. 1988; Stoffers et al. 1989) shows
that the hotspot volcanoes are surrounded by topographic lows (3600–3950 m
depth) bordered by deeper ([4000 m depth) abyssal hill regions representing an
ancient, 65 million year-old oceanic crust.
When assuming that the plate moves at a speed of 11 cm/yr over a fixed hotspot
(Heron 1972; Duncan et al. 1974; Minster and Jordan 1978), volcanic activities
within the hotspot must have taken place during the last 900,000 years. Also,
potassium-argon isotopic age dating carried out by Isabelle Le Roy in 1994
indicates that most submarine edifices are recent and go up in age to 550,000 years
old. The youngest island of the chain is Mehetia, whose last eruption took place
about 25000–73000 years ago (Leroy 1994).
Mehetia Island
The island formerly called ‘‘Meetia’’ or Mehetia lies 60 miles away from Tahiti
and is part of the Society volcanic chain. Captain Samuel Wallis first discovered
the Island on June 17, 1767. The island is now privately owned and is uninhabited
except for the presence of a few goats. Mehetia (2 km
2 ) is a volcanic cone and
rises 435 meters above the sea surface. It is about 4035 m high above the sea floor
of the Society hotspot (Fig. 9.4). The last volcanic eruption on the island was dated
as being 1 million years ago. During the last subaerial explosive eruption, a crater
150 m in diameter and 80 m deep was built. The only evidence of recent volcanism is found on the south flank of the volcano, at more than 1600 m depth, where
seismic activity was detected (Réseau Sismique Polynésien, RSP) from December
to April 1981. This was a target area for the submersible Cyana’s dive TH10 that
took place in 1989. Dive TH10 found evidence of recent underwater explosive
eruptions in the form of pyroclastic flows at 2301 m depth. The eruption took
place from a small parasite cone located on the southern flank of the island at
2300–2400 m depths (Figs. 9.5, 9.6).
This uninhabited island has vertical, volcanic cliffs, which makes the island
difficult to access. During the FS SONNE cruise of 1987, a group of German and
French scientists landed on the SW side to sample the island. Because of the strong
wave action on the rocky coast, the approach to the island was dangerous.
A zodiac was first sent with the ship’s captain, Hartmut Andresen, to explore the
The Society Hotspot
313