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Transcript for The Voyage of the Lee, segment 04 of 21
September, nineteen eighty-three - the Lee begins data collecting off the Juan de Fuca Ridge offshore Oregon and Washington. She is looking for mineral deposits associated with volcanic gases and fluids that seep out of active fractures on the sea floor. Scientists think these may be indicators of promising future mining sites for copper and gold. The Lee's search is aided by twentieth century technology in the form of underwater television. This is what the scientists see inside the fractures of the Juan de Fuca Ridge, one of the more complex geologic regions on earth, what scientists call a triple junction where three geologic elements come together in the form of active earthquake faults and ridges. The sound you hear is the steel frame of the camera hitting the walls of the sea floor. The camera is slowly being towed just astern of the Lee. At a depth of ten thousand feet there is little evidence of life, but it is nevertheless a dramatic surrealistic landscape that appears. These scenes are being recorded on videotape for later analysis by the Lee scientists. The underwater video is but one in an array of sophisticated devices that the Lee employs. The vessel, which is considered the chief marine research tool of the U. S. G. S., is equipped for numerous experiments. The Lee can, for instance, deploy a multi-hannel seismic streamer nearly two miles long. Hydrophones pick up sound waves bouncing off geological structures, showing a cross section of crust up to four miles below the floor of the Pacific. The Lee can also deploy shorter length seismic streamers which are trailed behind the ship to detect echoes of sound waves emitted by air guns. The hydrophones are used to map geological layers several hundred meters below the sea floor. The Lee comes equipped with a variety of air guns that can be towed in different arrays. Explosive bursts of air at two thousand pounds per square inch send energy equivalent to six sticks of dynamite bouncing into deep sea sediments and crusts. The sound waves do not have any adverse effect on sea life.
Sonar buoys are still another tool the vessel employs. These are launched overboard and float on the surface with a hydrophone hanging sixty feet in the water. It can relay by radio acoustic echoes picked up several miles behind the Lee. Magnetometers are towed about fifteen hundred feet astern to be free of the ship's metal. These devices detect variations in the earth's magnetic field which help reveal deep geology. A gravity meter is located onboard the Lee. It is as big as a suitcase, yet costs one million dollars. The gravity meter detects variations which hint at rock types and crustal thicknesses. Side-scan sonar looks like a torpedo. Towed as deep as six thousand meters, this device takes a sonar picture of sea floor topography up to one thousand meters wide. This is the T. V. camera sled which was taking the unusual pictures on Juan de Fuca Ridge. It can operate down to thirty thousand feet on a steel cable. It carries a videocamera and two still cameras. During the voyage, the Lee will make much use of dredges consisting of chain and clam shell buckets which will grab and haul up bottom samples of mud and rock. A gravity corer weighing from eight hundred to two thousand pounds will also be used. Cores of sediment show layers of materials from beneath the sea floor which help scientists date and evaluate the types of material which were laid down over millions of years. Finally, the Lee uses an instrument fixed inside its hull called a uniboom in which electrical pulses are generated in water shallower than one thousand meters. Reflections are picked up by hydrophones and printed out to visually show the layering beneath the ocean's floor.