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the water. Unlike the traverses made by submersibles that are perpendicular to the axis of the rift, Angus' traverses were basically parallel to the axis. This was not based on geological reasoning but on operational necessity. Traverses perpendicular to the axis were the most desired. But Angus needed to be within a few meters of the ocean floor to obtain the high quality of color images we sought. Since the fault scarps bounding the rift to either side run parallel to the axis, Angus tow lines were best run in the same direction to avoid countless collisions with the bottom. It was also along this same strike that we felt active vents would be found. As a result, the first Angus trackline resembled a slalom run, as the vehicle was towed from side to side down the strike of what we hoped was the central volcanic axis.

No sooner had Angus begun its first run before the temperature sensor on the vehicle indicated it had passed through an active vent area. Repeating its performance in the Galapagos Rift, the sled was recovered so that the color film could be processed in the portable laboratory that had been brought on the expedition for that purpose. But a review of the color film taken across the vent field revealed a scene different from those observed along the axis of the Galapagos Rift. Initially the scene was the same, as frame after frame showed the vehicle passing over a young volcanic terrain characterized by a fresh glassy lava surface.

The first indication of an approaching vent was not a rise in temperature but the appearance of small white Galathea crabs dotting the otherwise barren flows. Quickly this gradient of crabs increased, giving way to the larger and more densely packed sessile organisms, in particular, large white clams so typical of the Galapagos Rift vent fields. As the center of the field was approached, "milky" water could be seen along with an increase in the amount of particles in the water. But unlike the Galapagos vents, the center of the vent was not covered with tube worms and large clams. Instead, we saw a large yellowish-brown deposit of sediments largely devoid of life.

The coordinates of this vent site were transmitted by radio from the Melville to Jean Francheteau aboard Alvin's support ship Lulu. Since Alvin and Angus shared a common network of bottom transponders, it was easy to vector Alvin to any site discovered by Angus. Clearly, the role of submersibles was changing with the reconnaissance and regional mapping efforts falling more and more upon towed vehicle systems such as Angus. Towed vehicles had been used for several years to conduct regional mapping programs but it wasn't until 1977 to 1979 that joint operations between towed vehicles and manned submersibles became so closely choreographed.

What made this possible was the speed at which the photographic runs conducted by Angus were processed. Not only were tens of thousands of frames of color positive film quickly developed in a portable processing van for immediate viewing, but the edited tracks were also quickly plotted. This provided the geologists onboard with the opportunity to immediately generate detailed annotated traverses across the ocean floor. These traverses were then superimposed over the detailed bathymetric database to produce preliminary geologic maps. Each lowering added more and more detail to the evolving map of the area. The goal of this process was to space the Angus lines at just the right interval to permit the correlation of observations from one line to the next but not so closely as to produce highly redundant and, therefore, wasteful coverage.

On previous programs, a year or more had passed between the collection of towed vehicle data and follow-up dives by the submersible. Or even worse, the submersible conducted its own reconnaissance traverses working independent of towed vehicles. This was certainly the case with Projects FAMOUS and RITA.

On April 21, with the coordinates of an active hydrothermal field as their dive target, Alvin was lowered into the water. Dudley Foster was the pilot on this dive and as he dove over the fresh lava flows he began to see small white crabs on the horizon; he was reminded of similar scenes months before in the Galapagos Rift. But as he entered the vent field, it didn't feel the same. The water was much cloudier than usual. Then suddenly a tall chimney-like spire came into view; belching out its top was a dense black fluid resembling bellowing clouds of smoke. It looked like a steel factory as Alvin maneuvered above it for a closer view. But driving in midwater was proving difficult for Dudley; something was pulling him toward what he now called a "black smoker."

The pulling force proved to be the updraft or chimney effect caused by the rising black fluid. The black smoker was pulling water in from the side. And since Alvin was neutrally buoyant, it was also being pulled toward the smoker. Driving was made even more difficult as Dudley passed over the smoker and visual contact was lost in a thick cloud of black particles. Suddenly, he bumped against the chimney, which fell over like a giant fallen tree.

Ironically, this made the situation much better as the black fluid was now flowing out of the base o f the broken chimney instead of its top. Dudley could new turn on his variable ballast system and take in water, making Alvin negatively buoyant as it slowly landed on the bottom. Using his lift props, he now climbed a gentle mount surrounding the fallen chimney. Clearly, these structures were fragile since the entire mound, which was some ten meters in diameter and a few meters tall, consisted of numerous broken chimneys that had fallen before.

Since he was the first human to see such a feature, chimneys appeared to fall over naturally without the help of submersibles. As he approached the fallen chimney with black fluid flowing out of its base, he could see the chimney was hollow, lined by mineral crystals that reflected in the submersible's lights. Now that the submersible was resting firmly on the bottom, Dudley could bring his manipulator into play. Resting in Alvin's science tray was a temperature

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