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On the Alaskan Seafloor: Diving on the Kad'yak Wreck
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"Tracking Down Kad'yak"
August 26, 2004
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Measuring underwater artifacts (Courtesy
Tane Casserley, NOAA) [LARGER IMAGE] |
Archaeological excavations require specialized skills, painstaking
carefulness, time, and money. Underwater archaeological work
requires all of these things and more. Working in conditions with
far less visibility and limited time on the bottom requires special
training, which is available at only a handful of graduate
schools--and no undergraduate schools--across the country. A program
typically involves coursework and field schools. For
instance, students at East Carolina University, which sent out
archaeologists for the Kad'yak wreck, complete a two year M.A. degree
that includes summer and fall field schools during which students work on
actual sites. For instance, last summer they held a field school in
Alpina, Michigan, and focused on some of Lake Huron's 100 shipwrecks.
Along with specialized training, underwater archaeologists need
specialized gear to deal with different conditions. Water
temperature, for instance, dictates the type of suit worn. For Kad'yak,
which was located in water that measured 46 degrees Farenheit in
July, most divers wore dry suits. A dry suit has rubber seals at the
wrist, neck, and feet. These seals keep out water, and the entire
body stays dry except for the head, hands, and feet. Another option
in cold water is a conventional wet suit that is extremely thick,
which can protect skin against colder waters. Co-principle
investigator Tim Runyan, wore one such thick wet suit during dives.
Since salt water freezes at a lower temperature than fresh water,
divers can work in water below 32 degrees.
Divers must also choose what type of gas to breath, since that
affects the amount of time a diver can spend in the water. Although
several types of manufactured gases are available to divers (such as
Nitrox, Heliox, and Trimix), many dive on air. Although it allows
for less bottom time than a gas such as Trimix, which is a mix of
oxygen, helium, and nitrogen, air is easier to obtain. On the
Kad'yak wreck, archaeologists dived on air, which, combined with the
wreck's 80-foot depth, limited their time at the bottom to two
half-hour sessions per day.
Divers must be concerned not only with replacing oxygen, but also
with eliminating nitrogen that enters their system. The deeper one
dives, the less time there is to spend on the bottom and the more
decompression time must be taken to allow the body to rid itself of
nitrogen and become re-accustomed to normal atmospheric conditions.
On the Kad'yak dive, for instance, time at the bottom was only 30
minutes long at a depth of 80 feet, so there was no need for divers
to spend a large amount of time decompressing. Kad'yak divers would
spend just five minutes decompressing, hovering ten to 15 feet
below the water's surface. When divers push the limit of deep-sea
diving, they might reach depths of up to 500 feet, well over the
conventional 180-foot limit of scuba diving. At greater depths, the
body quickly absorbs nitrogen, which necessitates long decompression
periods. For instance, when divers worked on the U.S.S. Monitor off
Cape Hattaras, they worked at 240 feet for short periods of time.
They were supplied with air from the surface, which was pumped down
to them through tubes, and they had to go into a recompression
chamber for several hours after returning to the surface. If they
had they used Trimix, they would have had just 20 minutes on the
bottom and would have needed an hour to decompress at different
depths. Any way you cut it, the deeper one dives, the greater the
ratio of decompression time to actual bottom time becomes. One
reason that underwater archaeologists must always dive in pairs (at
least) is to keep careful track of their air supply and decompression
time.
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Underwater archaeologists plan on the
surface. (Courtesy Tane Casserley, NOAA) [LARGER IMAGE] |
Finally, underwater archaeologists must account for variable
visibility at the site on which they are working. The Kad'yak dive
was a survey of the site as opposed to an excavation. The archaeologists
essentially worked on producing maps on land for days from the few
hours that they spent measuring, triangulating, and photographing on
the bottom. The fact that the shipwreck was scattered over a few
hundred yards complicated matters.
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© 2004 by the Archaeological Institute of
America archive.archaeology.org/online/features/kadyak/archaeologists.html |