When the dive ended, we were pleased to return on board the Atlantis II and had
the surprise to find that a reception was prepared. The captain handed the pilot a
telex from Washington D.C. It was a message of congratulations from Massachusetts Senator Ted Kennedy.
Hess Deep: One Million Year Old EPR Crust Exposed
About one million years ago, the spreading of the EPR created a rifted structure
bounded by a depression with depths of more than 4,000 m, called the Hess Deep,
named after the famous scientist Harry Hess who did pioneering work in marine
geology in the 50–60 s (see Chap. 1). This area is located in a region near 2°14
0 N–
101°30
0 W which is North of the Galapagos Island in the Equatorial Pacific. It
consists of oceanic lithosphere created on the axis of the fast spreading East Pacific
Rise that was exposed during crustal uplift and faulting (Fig. 7.26a). Early works
in the 70’s by Russian scientists have reported that this EPR section has exposed
the lower crust and upper mantle rocks of peridotite and gabbros. In 1988, another
cruise called the Hymas II cruise organized by the University of Karlsruhe
(Germany) on the R.V. SONNE (Leg 60) also revealed the existence of similar
rocks in the trough of the Hess Deep.
This section of the EPR in the area of the Hess Deep represents a rifted structure
about 8 km wide and 25 km long oriented East–West, parallel to a more recent
spreading ridge called the Cocos-Nazca ridge. The Cocos-Nazca spreading ridge
extends from the Middle America trench (Central-eastern Pacific) westward. This
ridge system propagates towards the East Pacific Rise with a total spreading rate of
about 6 cm a year. The Cocos-Nazca ridge propagates westward and becomes less
significant and decreases in its volcanic activity. The northern wall of the Hess
Deep is the shallowest part of the EPR ridge, also called an Intra-Rift, and is
2,900–3,000 m deep, while the deeper trough is found at 3,750–4,400 m depth.
This Intra-Rift is an uplifted structure that has exposed deep-seated lower crust and
upper mantle peridotite-gabbros complexes (Fig. 7.26b). The other northern wall
bordering the Cocos-Nazca ridge propagator reaches shallower depths (2700 m)
and consists essentially of volcanic rocks, dykes and basaltic flows.
The first diving cruise in the Hess Deep took place with the Nautile and its
support ship Le NADIR in October–November 1988, during the Nazcopac (achronym for NAZca-COcos PACific) cruise.
Uncomfortable research vessels. For many years, until 1996, the
N.O. Le NADIR was the main support ship for the Nautile. This vessel of 56 m
long, 1,875 tons, commissioned in 1974, could carry 15 crewmembers and 25
scientists. When compared to other ocean going vessels, it already looked old at
the time it was built (Fig. 7.27). The NADIR has a flat keel, rides low on the sea,
there is limited space and it could be very uncomfortable to be on board. It rolls up
to 35–40° during average weather conditions. The ship is not adapted to spend
more than 30 days at sea. The accommodation quarters and water supply were
234
7 Oceanic Spreading Ridges and Sea Floor Creation
the surprise to find that a reception was prepared. The captain handed the pilot a
telex from Washington D.C. It was a message of congratulations from Massachusetts Senator Ted Kennedy.
Hess Deep: One Million Year Old EPR Crust Exposed
About one million years ago, the spreading of the EPR created a rifted structure
bounded by a depression with depths of more than 4,000 m, called the Hess Deep,
named after the famous scientist Harry Hess who did pioneering work in marine
geology in the 50–60 s (see Chap. 1). This area is located in a region near 2°14
0 N–
101°30
0 W which is North of the Galapagos Island in the Equatorial Pacific. It
consists of oceanic lithosphere created on the axis of the fast spreading East Pacific
Rise that was exposed during crustal uplift and faulting (Fig. 7.26a). Early works
in the 70’s by Russian scientists have reported that this EPR section has exposed
the lower crust and upper mantle rocks of peridotite and gabbros. In 1988, another
cruise called the Hymas II cruise organized by the University of Karlsruhe
(Germany) on the R.V. SONNE (Leg 60) also revealed the existence of similar
rocks in the trough of the Hess Deep.
This section of the EPR in the area of the Hess Deep represents a rifted structure
about 8 km wide and 25 km long oriented East–West, parallel to a more recent
spreading ridge called the Cocos-Nazca ridge. The Cocos-Nazca spreading ridge
extends from the Middle America trench (Central-eastern Pacific) westward. This
ridge system propagates towards the East Pacific Rise with a total spreading rate of
about 6 cm a year. The Cocos-Nazca ridge propagates westward and becomes less
significant and decreases in its volcanic activity. The northern wall of the Hess
Deep is the shallowest part of the EPR ridge, also called an Intra-Rift, and is
2,900–3,000 m deep, while the deeper trough is found at 3,750–4,400 m depth.
This Intra-Rift is an uplifted structure that has exposed deep-seated lower crust and
upper mantle peridotite-gabbros complexes (Fig. 7.26b). The other northern wall
bordering the Cocos-Nazca ridge propagator reaches shallower depths (2700 m)
and consists essentially of volcanic rocks, dykes and basaltic flows.
The first diving cruise in the Hess Deep took place with the Nautile and its
support ship Le NADIR in October–November 1988, during the Nazcopac (achronym for NAZca-COcos PACific) cruise.
Uncomfortable research vessels. For many years, until 1996, the
N.O. Le NADIR was the main support ship for the Nautile. This vessel of 56 m
long, 1,875 tons, commissioned in 1974, could carry 15 crewmembers and 25
scientists. When compared to other ocean going vessels, it already looked old at
the time it was built (Fig. 7.27). The NADIR has a flat keel, rides low on the sea,
there is limited space and it could be very uncomfortable to be on board. It rolls up
to 35–40° during average weather conditions. The ship is not adapted to spend
more than 30 days at sea. The accommodation quarters and water supply were
234
7 Oceanic Spreading Ridges and Sea Floor Creation