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 left
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 get plenty hot. When thewater
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.
