French-American Mid-Ocean Undersea Study

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French-American Mid-Ocean Undersea Study (abbreviated to FAMOUS, French - American Mid-Atlantic Undersea Study ) was the name of a research project that began in 1971, during the course of which there were diving trips to the Mid-Atlantic Ridge in 1973/74 , with new knowledge about the processes involved in drifting apart the clods of earth and the exact position of the dividing line were obtained. Xavier Le Pichon , James R. Heirtzler and Robert Ballard were in charge .

How the expedition came about and its objectives

The FAMOUS company resulted from a cooperation agreement between the US NOAA ( National Oceanic and Atmospheric Administration ) and the French CNEXO (Center national pour l'exploitation des océans), concluded in 1970 during a trip by President Pompidou . In November 1971, both sides were working during a meeting in Woods Hole from a text about the main goal of the action, the identification of phenomena at the edge of a nascent soil should be. The fact that an area around 400 nautical miles southwest of the Azores appeared to be optimal was due to the predictably good weather conditions there, the relative proximity of the deep water port of Ponta Delgada , a maximum water depth of 3000 meters and the intersection of the “rift” with a transform fault . In two phases, the Archimède was to undertake a few diving trips in August 1973 and the majority of the project would be carried out a year later in a joint effort. The assignment of the operational areas resulted from the characteristics of the available submersibles: the agile Cyana was the perfect match for the transform fault, which lay in the northwest of the study area, in the south the Alvin climbed along the side slopes of the ditch, and the clumsy Archimède crossed there in the north the bottom of the trench where the transform fault abruptly interrupts it.

Burglar ditch or conveyor belt up

Research vessel Knorr in 2011

The equipment used on the expedition also included the Glomar Challenger , which could be recognized from afar by its derrick. In order to be able to draw the correct conclusions from the drill cores obtained, it was useful to have a seabed mapped as precisely as possible . The ship of the US Navy Knorr initially took care of this . By the beginning of 1974, the Americans had managed to photograph the entire area using a process called Libec (Light Behind Camera) and use sonar equipment to create maps for the dives. The state-of-the-art equipped Knorr also had other tasks: the catamaran Lulu was the mother ship for the submersible Alvin , but the rather small Lulu itself was looked after by Knorr. In addition, Knorr dragged kilometers of thermal probes across the ocean floor to find water with abnormally high temperatures, but in vain. It was very important to monitor the earthquake activity by means of seismographs and detectors-equipped buoys, not only for scientific reasons, but for the safety of the submersible boats, whose resistance to pressure waves at critical depths should not be tested.

So the campaign was largely overseas and the submersibles were just spearheads. Under the sea, the three by six kilometer area was fictitiously marked with two intersecting stretches on which the Alvin systematically took samples in 400 meter steps. The question was whether the large crevice volcanoes in the center of the depression indicated the boundary between the American and African plates or whether the elevations running parallel to the two steep walls at their bases also showed volcanism. Of course, the question of how the ditch was created also arose. Was an underground magma chamber gradually emptying and collapsing or has this valley always existed and a conveyor belt-like mechanism transports the earth's crust that is newly formed on the inner valley floor to the highest level of the adjacent mountains? Could the inner valley floor as a whole represent a border area with randomly distributed volcanism? Gaps were found parallel to the trench depression with a height difference of 10 to 20 meters between the edges; the further away from the center, the greater the offset. The observed density of such faults was not expected. Ultimately, the movement along the edges of the clod was proven and thus the conveyor belt theory of Harry Hammond Hess was confirmed. For the geologists involved, it became clear how the fracture point is shaped by the large faults that form in the newly formed oceanic crust. With a maximum width of 1 km, the edge areas turned out to be surprisingly narrow, but also very complex. The formation of the faults is a continuous process, while volcanic activity occurs only sporadically in a central area 0.5 to 1 km wide. A side effect of the successful implementation of the FAMOUS project for the scientists in the USA was an expansion of the possibilities for using funds from the US Navy (e.g. Trieste , Sea Cliff and Sea Turtle ).

Transform fault and hydrothermal deposits

From the French side, the naval ship D'Entrecasteaux had depicted the deep sea floor in May 1972 with an extremely focused echo sounder beam in a way that was not yet known until then. The resulting maps were very helpful for the dives with their ten meters apart contour lines, but those details of the bottom topography that provided information about their formation and geological composition were in the range of half a meter and smaller, which is the authorization for the submersible -Entry arose. The investigated 20-kilometer-long transform fault is one of the many interruptions in the trench depression in which its sections are offset at right angles. Conceptually, a distinction was made between the transform valley (about 3 km wide and 600 m deep compared to the sea floor) and the still active transform fault zone (maximum 1 km wide), which presented itself as a V-shaped incision with relatively steep slopes. The speed of movement of the two plateaus is assumed to be 1 cm / year, resulting in an age of the transform fault zone of 1 million years. The cross-section of the Transform Valley was covered in ten dives. With its sequence of vertical staggered breaks, the slope was reminiscent of a staircase with 10-meter-wide steps and one looked out for traces of movement on the fault fronts - grinding marks in the rock were suitable for demonstrating sliding. A "beautiful fragment with very fresh breaklines and clear foliation " provided evidence of the underlying model under the magnifying glass with its grinding traces, and since those were at a 45 degree angle to the horizontal, also that of an additional vertical movement of the north wall. In addition, this thesis was confirmed, which is called “left- sided shift” and in the affected terrain means a shift to the west of the American clod beginning with the north slope.

Manganese nodule from the mid-Atlantic ridge

A chance find also led to the first finding of the mouth of a spring, as it is necessary for the formation of hydrothermal deposits . A rock sample initially mistaken for flat lava through the porthole of Cyana turned out to be a hydrothermal precipitate on closer examination: almost solid manganese . The field of these deposits was about 15 by 40 meters and therefore the retrieval was largely tied to the memory of the scientist who first collected the sample. But it succeeded: On July 26, 1974, the Cyana found the crevice that was half a meter wide and several meters long. The mouth of the spring was laid out with rust-red concretions , but at this point it was not noticeably active.

public relation

After the first phase of the FAMOUS company, a press conference was held in Paris in October 1973 by the French Minister of Industry and Research, Charbonnel, which made it clear to the science journalists who attended the broad framework and the successes of the first diving trips. The perceptible public interest caused the media to send their reporters to the area of ​​operation the following year, and NOAA and CNEXO chartered the three-master Bel Espoir , from which the press people witnessed the diving tests on site.

Critical situations

  • On August 5, 1973, a short circuit in the diving ball of the Archimède caused a small fire with heavy smoke development. The three crew members grabbed their personal emergency breathing apparatus , but Bob Ballard's one did not appear to be working. But it was just an unopened oxygen tap that almost choked him.
  • In the last tests off Toulon , water had shot violently through the edge of the tower hatch at the beginning of a dive, also at the Archimède . The crew's first thought was that the hatch was not properly closed, but another explanation was found: Of those iron shot pellets used as ballast , two or three fell on the hatch seal when it was filled, enough to cause a leak.
  • On June 29, 1974, the manned Cyana had to go into water for the first time , but a very rough, critically high swell and an inexperienced crew of the mother ship Le Noroît met each other, which caused the submersible to lurch over the deck after a stabilization line was torn and made it unusable for a few days made. In addition, one initially struggled with failures of the drive motors.
  • On July 17, 1974, the Alvin examined a Gjá and set down on its bottom at a depth of 2,800 meters to take samples. However, there was a current in the 30 meter deep and 6 meter wide crevice that pushed the submersible into a narrower part and also turned it. It took two and a half hours to free the Alvin from her predicament by means of maneuvers in the range of centimeters.

Yield of material

Contrary to initial doubts about their usefulness for scientific purposes, the three manned submersibles could be used successfully from their mother ships. The examined section of the rupture point, at which the American and European-African continental blocks slide apart, presented itself as a deep trough 1 to 5 km wide and 40 km long, which in turn lies in a wider valley. The three submersibles covered a total of 91 kilometers on the sea floor in 51 trips and collected two tons of precisely selected rock at 167 locations. The 228 hours on the sea floor were reflected in 23,000 photos and television recordings lasting 108 hours. Even before the second campaign, the work of around 20 surface ships ensured that diving was carried out in the most precisely known underwater area, while that of the submersibles brought the innovation that geophysical data no longer obtained on land had to be transferred to the Atlantic.

literature

  • Claude Riffaud, Xavier Le Pichon: Expedition "Famous". 3000 meters below the Atlantic. Kiepenheuer & Witsch, Cologne 1977, ISBN 978-3-59-623521-6 .

credentials

Web links

Individual evidence

  1. ^ Riffaud / Le Pichon 1977: 8
  2. ^ Riffaud / Le Pichon 1977: 116
  3. ^ Riffaud / Le Pichon 1977: 118
  4. ^ Riffaud / Le Pichon 1977: 119
  5. ^ Riffaud / Le Pichon 1977: 271
  6. ^ Riffaud / Le Pichon 1977: 269
  7. ^ Riffaud / Le Pichon 1977: 287
  8. ^ Riffaud / Le Pichon 1977: 285
  9. ^ Riffaud / Le Pichon 1977: 293
  10. ↑ Jean Francheteau et al. a .: Transform Fault and Rift Valley from Bathyscaph and Diving Saucer. Science, New Series, Volume 190, No. 4210, October 10, 1975, p. 108. PDF file, 798 kB
  11. ^ Riffaud / Le Pichon 1977: 24
  12. ^ Riffaud / Le Pichon 1977: 186
  13. ^ Riffaud / Le Pichon 1977: 266
  14. ^ Riffaud / Le Pichon 1977: 204
  15. ^ Riffaud / Le Pichon 1977: 246
  16. ^ Riffaud / Le Pichon 1977: 255
  17. ^ Riffaud / Le Pichon 1977: 240
  18. ^ Riffaud / Le Pichon 1977: 154
  19. ^ Riffaud / Le Pichon 1977: 195
  20. ^ Riffaud / Le Pichon 1977: 162
  21. ^ Riffaud / Le Pichon 1977: 277
  22. ^ Riffaud / Le Pichon 1977: 290