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Transcript
The Lowest Elevation.... The Dead Sea
From extremescience.com, February 2010
Why is it Called the Dead Sea?
Satellite view of the Dead Sea. NASA.
Sounds kinda creepy, doesn't it? The name 'Dead Sea' is actually a
kinder, gentler translation from the Hebrew name 'Yam ha Maved',
which means, 'Killer Sea'. It is some of the saltiest water anywhere
in the world, almost six times as salty as the ocean! The Dead Sea
is completely landlocked and it gets saltier with increasing depth.
The surface, fed by the River Jordan, is the least saline. Down to
about 130 feet (40 meters), the seawater comprises about 300
grams of salt per kilogram of seawater. That's about ten times the
salinity of the oceans. Below 300 feet, though, the sea has 332
grams of salt per kilogram of seawater and is saturated. Salt
precipitates out and piles up on the bottom of the sea.
There are no fish or any kind of swimming, squirming creatures living in or near the water. There are, however,
several types of bacteria and one type of algea that have adapted to harsh life in the waters of the Dead Sea.
What you'll see on the shores of the Sea is white, crystals of salt covering EVERYTHING. And this is no
ordinary table salt, either. The salts found in the Dead Sea are mineral salts, just like you find in the oceans of
the world, only in extreme concentrations. The water in the Dead Sea is deadly to living things. Fish
accidentally swimming into the waters from one of the several freshwater streams that feed the Sea are killed
instantly, their bodies quickly coated with a preserving layer of salt crystals and then tossed onto shore by the
wind and waves. Brutal!
The guy to the left is actually floating in the Dead Sea. "But, hey, I thought you
said the Dead Sea was DEADLY!" Not to us. Humans are remarkably adaptable.
We can swim in the Dead Sea, just like we can swim in the ocean. Well, people
don't really "swim" in the Dead Sea - they just "hang out". That's what's so cool
about the Dead Sea. Because of the extremely high concentration of dissolved
mineral salts in the water its density is way more than that of plain old fresh
water. What this means is our bodies are more buoyant in the Dead Sea - so you
bob like a cork. In fact, people are so buoyant in this water, it makes it kinda
tough to actually swim. Most people like to just kick back in the water and read. It almost looks as though this
guy is sitting on an air mattress that has sunk below the surface, but he's not. He's really just floating, without
having to hold is feet in that position! If you think this is easy, try floating like this in a freshwater swimming
pool.
What Caused the Dead Sea to Form?
This lesson takes us back to the subject of plate tectonics. In this part of
the world there is a rift forming where two crustal plates are spreading
apart. The East Rift Valley runs through most of Africa, but it starts north
of the Dead Sea and runs south along the eastern side of the continent. The
Sea is located right along the Rift Valley where the earth's crust is being
stretched thin. To get an idea of how this "crustal spreading" thing works,
take a bar of taffy, or taffy-like candy and try to pull it apart. You'll see
where the candy starts to come apart it gets really thin just before it breaks.
That's what is happening to the earth's crust in the Rift Valley. Where the earth's crust gets thin, that part of the
surface sinks downward. Look at the picture at right to see how the rift forms, sinking downward where the
crust is stretched thin. You know what? The Dead Sea is still sinking lower, even today. Scientists figure that
the Dead Sea lowers by as much as 13 inches per year. On a geologic time scale that's incredibly fast!
Why is the Dead Sea so Salty?
We talked about how the surface of the Sea got down so low in elevation, but why is it so salty? All roads lead
to the Sea when it comes to the rivers in the area. The Dead Sea is continually fed water from the rivers and
streams coming down off the mountains that surround it. But the kicker is this....no rivers drain out of the Dead
Sea. The only way water gets out of the Sea is through evaporation. And boy does it evaporate! This part of the
world gets plenty hot. When the water evaporates, it leaves behind all the dissolved minerals in the Sea, just
making it saltier. In fact, it's through the dual action of; 1) continuing evaporation and 2) minerals salts carried
into the Sea from the local rivers, that makes the Sea so salty. The fact that the water doesn't escape the Sea just
traps the salts within its shores. There's nothing living in the Dead Sea because it got so salty, so quickly, that
evolution has not had a chance to produce any creatures that could adapt to such brutal conditions.