This is Rachel Haymon, a marine geologist at the University of California at Santa Barbara, describing her return in April 1991 in the submersible Alvin to a troughlike volcanic caldera on the crest of the East Pacific Rise, a place where 15 months earlier she had seen hot springs teeming with animal life, a place she thought she knew well--latitude, 9 degrees, 50 minutes north; longitude, 104 degrees, 18 minutes west; depth, 8,500 feet below the ocean surface: The whole area had completely changed. We found only these little tiny crabs that looked like they were five days old. We drove all over, and we didn’t find any dense communities of hot- spring animals--zero tube worms. Everything looked different.
Daniel Fornari, a marine geologist at Lamont-Doherty Geological Observatory, was also on the cruise: The first thing a marine geologist thinks about is, ‘Are you lost? Have you screwed up in some fundamental way?’ But after all this gnashing of teeth, we finally figured out, ‘No, we’re in the right place.’ Then the sub went down again, and the divers couldn’t see a thing. I mean it was inky black--it was this smoky water. Well, this was not what it was like in 1989. This was a dramatic change.
Haymon: Then on our fourteenth dive, we found this community of thousands of tube worms and mussels--dead. They were scorched and shredded and blown up. Some of them were still alive, looking absolutely pitiful. The meat was just lying there--nothing had touched it. There were hardly any scavengers, like crabs, which given all this free food was really amazing. And on top of all this was what looked like a gray ash. It had pyrrhotite and sulfate--hydrothermal minerals--in it, and pieces of dead flesh. Whatever happened was a sudden violent event that destroyed the animals and rained all this ash on them. We collected some tube worms, and when we brought them up on deck the smell was kind of like hamburger on the grill.
Richard Lutz, deep-sea biologist, Rutgers University: One of the tube worms had what looked like a chunk of black basalt at the bottom--tube worms are often attached to basalt--but when we looked in detail it was charcoal-broiled trophosome, a piece of the tube worm’s tissue. That was one reason for calling this site the Tube-worm Barbecue.
Karen Von Damm, water chemist, University of New Hampshire: The most impressive thing was that there was hot water coming out everywhere on the seafloor. Usually you see it coming out of a few cracks. Here it was everywhere, and it had this white stuff in it. It was literally like driving through a blizzard--not a snowstorm, a blizzard. The seafloor is usually black, but here it was all white. It was amazing!
Haymon: What it was was bacteria--white, fluffy material--that was getting blasted up into the water, 150 feet above the seafloor, by hydrothermal vents.
Fornari: We ended up calling them snowblowers, because that’s exactly what they looked like. In some places, the whole caldera was this ghostly chasm of fresh volcanic rock, black and glassy, covered in white bacterial matting with these snowblowers going. It was an astounding, astounding terrain.
Von Damm: We saw one vent that was 389 degrees Celsius [732 Fahrenheit] one day, then 396 degrees a week later, and 403 degrees a week after that. Nobody had ever seen temperatures change like that. This was 400-degree water, and it was pouring out of a pile of rock! Basically it had boiled under the seafloor. You can think of it as steam, but it’s under such high pressure that it’s like a liquid.
Fornari: So we knew that something was up. It didn’t dawn on us right away because we were unwilling, I think, to accept the obvious--no one had ever witnessed an eruption on the seafloor before.
Haymon: We gave some lava to Ken Rubin at Scripps, who has a technique for dating young lavas. He calculated that the eruption happened between March 28 and April 6. Our first dive was on April 1.
What I believe happened is that magma came up from below, like a piston, and it had to displace the water in the void spaces in the crust. But the boiling water was being confined from above by a thin cap of magma that had flowed out over the area earlier, partially buried the tube worms, and cooled and hardened. So the pressure built up until the cap was just blown away. It could have been a matter of only a few minutes between the flow that formed the cap and the explosion--lava cools immediately in cold seawater.
Then you have water rushing out of the seafloor, flying tube worms, and glass flying all over. The glass may be what tore up the tube worms--or maybe they just exploded like hot dogs in a microwave. The hydrothermal minerals that formed under the seafloor, I think, blew out with the water and formed the gray ash we saw.
Not long ago it was thought that the seafloor was a motionless, timeless place, billions of years old, almost as old as the planet itself. Now it is known that the seafloor is the youngest part of Earth, nowhere more than 200 million years old and constantly being created anew. It is created at the midocean ridge, which winds around the planet in a sinuous band and which includes the East Pacific Rise. Along the crest of the rise at 9 degrees, 50 minutes north, in a caldera that is no more than 50 feet deep and 650 feet wide, the ocean floor cracks and spreads apart, and magma wells up from Earth’s interior to form new ocean floor. What Haymon and her colleagues saw in April 1991 was an instant of geologic creation.
Not long ago too, it was thought that life on the seafloor was a sparse and slow affair, sustained only by occasional scraps of food falling from the sea surface. Then in 1977 divers in the Alvin discovered the first deep-sea hot springs near the Galápagos. There and at other hydrothermal vents, researchers found a new type of food chain, based not on sunlight but on the oxidation of hydrogen sulfide spewing from the vents. Bacteria did the oxidizing, and they nourished huge tube worms and mussels and clams--all packed together, along with crabs and other scavengers, in an extraordinarily dense ecosystem. Biologists still haven’t figured out how such an ecosystem gets assembled, in part because they had never seen one at the moment of its birth. Hence their excitement about the find at 9 degrees, 50 minutes north. What Haymon and her colleagues saw was an instant of ecological creation.
In March of this year, 11 months after their previous visit, they went back. They went back to the Tube-worm Barbecue; to the Hole to Hell, another place where lava erupted last year; to the Tube-worm Pillar, a 35- foot-high column of older, frozen lava encrusted right to the top with tube worms, which survived when fresh lava lapped around the base of the pillar; and to the Valley of the Shadow of Death, where Haymon and two companions had bumbled around in the inky smoke.
This is Rachel Haymon describing what she saw when she returned to the Tube-worm Barbecue: It looked like a totally different place. All the iron sulfide in that gray sediment had oxidized to orange, so the site was just blanketed in orange. When we had seen oxidized sediments around a hydrothermal area before, we had tended to assume it was an old site--tens to hundreds of years old at least--but obviously it does not take that long at all. In 1991 this area also had warm water pouring out of a big, gaping ten-foot-wide fissure; in ’92 there was no venting. There were still tube- worm casings littering the floor, but there was not a shred of fresh tissue left. There were a lot of fish, little white octopuses, crabs. Anything that could move, that could swim in or crawl in, was there and was consuming what was left of the tube worms.
Lutz: And the Barbecue was not nearly as interesting as the sites that were newly formed hydrothermal vents. At one site, where the water was coming out of bare basalt last year, there was a 16-foot-high black smoker. That’s a pretty impressive rock to see that wasn’t there 11 months earlier. And at the Hole to Hell there were tremendous quantities of Tevnia tube worms--accordion-shaped tubes a foot long. There were thousands of these animals.
Fornari: It was astounding the change that we saw. All of the areas that had been white, white, white with bacterial mats and snowblowers everywhere--there was now very little bacterial mat. All the little tiny crabs we saw before--the area was now covered with crabs that were big and fat.
Haymon: So we realized that the bacteria were being eaten. Last year the bacteria were the only organisms around, without anything to eat them. This year they were getting munched back. People always thought the crabs were scavengers that would come in later. They were not seen as feeding on bacteria. But the Valley of the Shadow of Death went from having no animals to having zillions of crabs. We changed the name to the Valley of the Crabs.
I’m not a biologist, but it makes a nice story, and it may be what happened: When you have an eruption, it’s almost like springtime on the seafloor. These sulfur-oxidizing bacteria go nuts--instead of a greening of the seafloor it’s a whitening of the seafloor. That then provides a food source that causes a population burst in all the grazers. In addition, there are geochemical changes that are like a trigger to the organisms that it’s spawning time. I don’t know whether that’s true. But definitely a lot of them got the message.
Lutz: This is the first time we’re going to be able to document biological succession from the beginning. We know we’re dealing with the birth of a hydrothermal field, and we can now follow things from time zero and look at the changes. I feel we’ll have a spectacular, full-grown community in two to three years.
Haymon: I would predict the place will probably erupt again. The system as a whole is not cooling down, so I would say there’s a good likelihood that if we keep tracking this area, we’re going to see it erupt again within five years.
Von Damm: It used to be that people said one of the last great things to see on the seafloor would be an eruption actually happening--to see the red lava flowing on the seafloor. We don’t really know what it would be like. It might be a very turbulent event. But after coming this close, I don’t want to see red lava flowing on the seafloor. A few days later is close enough for me.