1979 - The “Smoking” Gun

21°N

Fresh from its epic dives to examine the new-found communities of life around the Galápagos Rift vents, Alvin headed north aboard R/V/ Lulu in April 1979. They joined a U.S.-French expedition that was exploring another section of the Mid-Ocean Ridge called the East Pacific Rise. The site was 1,800 miles north of the Galápagos Rift, just beyond the mouth of the Gulf of California at latitude 21°N. The U.S. group was led by Scripps scientists Fred Spiess and Ken Macdonald on board R/V Melville.

The year before, the French had done scouting work in the area. The submersible Cyana, a veteran of Project FAMOUS, dove into the valley of the rift. Scientists on board Cyana did not see any hydrothermal vents, but they did collect many rock samples. One rock looked like a long tube and had glistening crystals. But the unusual specimen was among hundreds that were collected. So it was not closely analyzed until months later.

The analysis showed that the rock was made of sphalerite (zinc sulfide). The specimen was full of metals—mostly zinc, but also iron and copper, and traces of lead and silver. That was intriguing, because to make a mineral such as sphalerite, you need extremely hot water—much hotter than the 23°C. (73°F) fluids measured at the Galápagos Rift.

Superheated water at freezing depths

On April 21, 1979, Alvin dove in search of hydrothermal vents. Bill Normark of the U.S. Geological Survey and Thierry Juteau, a French volcanologistst, were the scientific observers. The pilot was Dudley Foster. He followed a trail of white clams on the seafloor. By now, everyone knew they would likely lead to vents.

Suddenly, the scientists came upon something no human had ever seen before. A tall spire of rock, about six feet tall, was sticking out of the seafloor. A jet of black fluid spewed out of the top—like smoke out of a chimney. Foster said it looked like smoke belching out of the smokestack of a steaming locomotive.

Foster approached to take a closer look. Hot, black fluids rushed powerfully upward from the chimney-like rock. It created an updraft that made it harder to steer Alvin. Foster knocked into the chimney. It crumbled, making a wider hole that let out a billowing cloud of black “smoke.” It became harder to see.

Using Alvin’s manipulator arm, Foster grabbed a probe to measure the temperature of the fluids. The reading inside Alvin’s sphere zoomed as high as it could go—to 32.7°C (91°F). The scientists thought it was a mistake and tried again. Again, the temperature reading shot up to the limit.

By now, Foster wanted to get out of the black cloud and moved on to another vent. He didn’t even bother to take a temperature reading because he assumed the probe wasn’t working properly.

Smoke and minerals

When Alvin surfaced on April 21, 1979, Alvin engineer Jim Akens went to see what went wrong with the temperature probe that he had built. To his surprise, he found that the probe’s plastic tip had melted. That type of plastic melted at temperatures of 180°C (356°F)!

Alvin’s viewports were made of the same plastic. The viewports had been only a few feet away from the same hot fluids that melted the temperature probe!

Akens made a new probe that could measure higher temperatures. Scientists in Alvin used it to measure black-smoker hydrothermal vent fluids that reached 350°C (662°F). This was the temperature that MIT geochemist Edmonds had said was possible after he analyzed the lower-temperature hydrothermal fluids from the 1977 cruise. But most people could not easily believe it.

Temperatures of 350°C are hot enough to cause chemical reactions that extract metals from ocean crust rocks and dissolve the metals into hydrothermal fluids. When the superheated fluids hit cold, oxygen-rich seawater, the metals dissolved in the fluids come out of solution (or “precipitate”). Fluids erupting out of the vents become filled with dark metal particles—creating the illusion of “smoke.”

Precipitating minerals form “blacker-smoker” chimneys that can grow very tall. The tallest one found so far was a structure on the Juan de Fuca Ridge, which scientists called “Godzilla.” It reached 16 stories high before it toppled over.

The year of 1979 was a turning point for hydrothermal vent discovery and research. At Galápagos, hydrothermal vents were shown to be a warm womb that nourished an amazing diversity of life in the dark depths. At 21°N, scientists discovered black smoker chimneys spewing scalding hot fluids for the first time. They saw that hydrothermal vents were also great furnaces, where many of Earth’s great ore deposits were made.

Related Interview:

Dudley Foster, Alvin pilot, discusses finding high temperature vents at 21°N on the 1979 expedition.

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