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Lost City Expedition: Mission

April 30, 2003 -- The Alien Environment

Jeff Karson


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Today's Question

Q. How do the big valleys form on the face of the Atlantis Mountain actually form?

A.We believe that these valleys or escarpments form by a couple processes. The south face of the mountain is bounded by the Atlantis Fracture Zone, which has numerous small earthquakes every year. In addition, alteration of the rocks along the southern face causes them to expand by as much as 40%. This expansion may cause the rocks that form the very steep hillsides to fracture and become unstable. This process, coupled with shaking by the earthquakes may result in landslides, which progressively eat away at the mountain.

karson image

Every time I make a dive in Alvin or see the other members of our group descend beneath the waves I think of how much it is like traveling to another planet in a spaceship. Even though it is part of our own Earth, the part of it we travel to could not be more different from what we are all used to on land.

When we go to the seafloor there is no sunlight, and the only light we have comes from the battery-operated lights on Alvin. With no sunlight, there is no photosynthesis and none of the green plants that we have on land. Because there is no grass, no weeds, and no trees, the animals that live off of them don't exist either.

Away from the hydrothermal vents, there is very little life on the seafloor.
Instead of air, we are surrounded by an ‘at-mosphere’ of much thicker seawater that is under tremendous pressure because of the great depths to which we go. Without the artificial atmosphere sealed inside Alvin we would stand about as much chance of surviving on the seafloor as we would on the Moon or Mars. Not many animals have adapted to live in this extreme environment, so much of the seafloor looks something like a desert with living organisms concentrated around the hydrothermal vents like the Lost City, an isolated oasis. On the deep seafloor, there are no seasons and no weather. There is only cold water that moves under the influence of deep currents and tides. This is where we have to go to find out how the Lost City was formed.
Fractures in the rock provide a pathway for fluid flow.

My own particular fascination with this alien environment is the rocks. Even these are different from most of the rocks we see on land which are parts of the continents. The rocks of the seafloor are mostly darker and denser. Out here near the Mid-Atlantic Ridge, where the oceanic crust is very young (less than 1 million years old, that’s young in geological terms) we find mountains, like the Atlantis Massif, of basaltic lavas and peridotite mantle rocks. Huge cliffs, rivaling the walls of the Grand Canyon of the Colorado River, have been created by giant fault zones and rock slides. These areas allow us to study rocks that formed deep beneath the spreading center and that form the foundation of the Lost City Hydrothermal Field.

On another note, the members of the Lost City Expedition would like to congratulate Betsy Williams on her first Alvin dive. As she stepped out of the sub, she received the traditional congratulatory gesture-- several buckets of cold ice water!

For the fluids that emanate from the spires and flanges in the field, there must be fractures and fault zones in the underlying rock that allow those fluids to flow out to the seafloor. Part of our investigation focuseson understanding this “plumbing system” beneath the Lost City.To do this we are mapping out all the fractures that we can find in the area and taking special note of those that allowed the flow of hydrothermal fluids. These are easy to spot because they have white carbonate deposits in them. As our dive series continues, we hope that our investigations of the surrounding rocks will help us better understand how they contributed to the development of the Lost City.