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Mysteries of the Deep
2.6 km Down on the Bottom of the Sea Floor


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Olivia


by Cornel De Ronde

On January 4, 1999, pilot Blee Williams, geologist Cornel de Ronde and helium expert Ron Greene descended into the murky depths of the Pacific Ocean in the deep submersible vehicle Alvin. They were in search of hot springs, or black smokers, known to exist more than 2.6 km down on the bottom of the ocean floor.

The target of the dive is known as the East Pacific Rise, a long chain of submarine mountains that stretch many thousands of kilometers from the north Pacific to Antarctica. Eruptions of hot lava onto the crest of this oceanic mountain chain are quite common. Cold seawater seeps through deep cracks in sea floor and is heated by the hot lava.

An hour and a half after beginning the descent, the three passengers aboard Alvin found themselves peering out of the small portholes and trying to see their first images of the sea floor. The pilot turned on the exterior floodlights and the sonar told them that the bottom was only 50 meters away. And there it was!

Directly beneath Alvin were various lava flows, described as 'lobate flows', reminiscent of toothpaste being squeezed from the tube.

The submersible moved and soon came upon a very steep wall that had a series of vertical steps each about eight to ten meters tall, with the intervening slopes covered by talus­jumbled, broken fragments of lava. Later the site was dubbed "Wall Street."

After a short while the three explorers found what they had been seeking­numerous chimneys belching out thick clouds of black smoke that rose into the seawater for 200 meters. The hydrothermic fluids pouring from the chimneys, or vents, exceeded 350°C, hot enough to have various metals such as copper, lead, zinc and sometimes gold dissolved in the water.

When this hot water mixes with the cold (around 2°C) ambient seawater, chemical reactions take place and the metals no longer stay in solution but precipitate out as very small, metal-rich, particles. Hence the name black smokers, as the chimneys (typically one to twelve meters in height with their vigorous plumes of black smoke) look remarkably like smoke stacks in an industrial area.

The scientists directed the pilot to the next target and the next five to six hours were spent sampling the hot water gushing from vents and retrieving pieces of the metal-rich chimney for chemical analyses in the laboratory. All of the samples were taken with the robotic manipulator arms on Alvin, expertly controlled by the pilot. Extensive videos were taken, chimney structures and the surrounding geology were mapped and some crabs and worms were collected for the biologists back on Atlantis.

All-in-all, the time spent on the bottom was hectic and passed far too quickly. It was spent in a world so vastly different and removed from what we know on the surface of the Earth that the three divers could imagine being on another planet.

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