On the edge of the Dead Sea, the ground is caving in. Trucks
and small buildings in Israel and Jordan have fallen into pits, beaches
and plantations have closed, and roads been rerouted to avoid the more
than 5500 sinkholes that pockmark the region. Now, scientists think they
have a better idea of what’s causing these sinkholes to form—and how to
stop them.
The Dead Sea is shrinking dramatically, falling 0.9 meters a year.
The Jordan River—its main source of freshwater—has been mostly diverted
for agriculture, and industrial plants have kept siphoning off Dead Sea
water for mineral extraction. Scientists think that the receding
shoreline is the driving force behind the sinkholes, but they’ve lacked
hard evidence of what’s happening underground.
So, as part of an initiative by the Geological Survey of Israel to
study the Dead Sea region, Imri Oz, a hydrogeologist currently at
Technion - Israel Institute of Technology in Haifa, and his colleagues
built their own version of the Dead Sea. In a sand-filled Plexiglas tank
in the lab, they constructed a miniature cross section of the sea’s
shore. The Dead Sea’s famously salty water flows in from a hole on one
side, and freshwater (representing the flow from nearby underground
aquifers) seeps in from the other. The team used information from
boreholes drilled around the Dead Sea to estimate the depth of different
layers of clay, gravel, salt, and sand and their respective particle
sizes.
In the model, sinkholes grew just as they do in the real world: As
the Dead Sea’s water level drops, freshwater flows in from nearby
aquifers to replace it. The freshwater flows through underground layers
of salt and dissolves it, leaving behind unstable caverns. Small pockets
then collapsed to form depressions in the sand. Scaled up to the real
world, those depressions are sinkholes. The model also gave insight into
the timing of sinkhole formation: Large blocks of salt were more likely
to collapse all at once, whereas smaller salt deposits showed a slump
on the surface before caving in.
Through ongoing studies into the structure of the Dead Sea’s salt
deposits and ground-penetrating radar studies to track incipient
sinkholes, scientists can now identify the worst spots. Stopping new
sinkholes from opening, however, is more difficult. The most popular
proposed solution has been a canal or pipeline to refill the Dead Sea
using water from the Red Sea or the Mediterranean Sea—the nearest
unlimited water sources. Politicians have hailed various proposals as
peace projects—opportunities for cooperation among Israelis, Jordanians,
and Palestinians, all of which could benefit from the water as it made
its way toward the Dead Sea. But no pipelines have been built, in part
because of the need for more study.
Satellite images reveal the Dead Sea’s
retreat, as well as the growth of mineral-extraction evaporation ponds
in the southern basin.
NASA's Earth Observatory
To find out whether the strategy would work, Oz’s team simulated the
effects of a Red Sea–Dead Sea pipeline by adding to their tank slightly
salty water—like that of the Red Sea. The results were encouraging:
The new “sea water” formed a layer on top of the even saltier Dead Sea
water, and flowed back up into the simulated aquifer, effectively
plugging it. Though the seawater still dissolved the salt layers, it did
so much more slowly than the flow of freshwater. In the real world,
salt deposits would dissolve about 10 times more slowly than they
currently do if the Dead Sea were refilled, the researchers report this
month in the Journal of Geophysical Research: Earth Surface.
“It’s really interesting to see the dynamic evolution that the model
predicts, and how it explains what we observe on the surface,” says
Simone Atzori, a geophysicist at the National Institute of Geophysics
and Volcanology in Rome, who was not involved with the study. “Through
this model, they tried to give us visual access to this phenomenon.”
Of course, sand in a Plexiglas tank does not reflect the complexities
of actual sinkholes. “This is always the problem with the laboratory,
that you’re taking the real world and putting it into a smaller system,”
Oz says. The model also can’t account for the potential environmental
impacts of a pipeline, such as massive algal blooms.
The addition of seawater might cause algae to grow out of control,
choking out microorganisms better suited to a saltier environment, or
turning the water red. Environmentalists also worry that the seawater
could trigger the growth of tiny, floating gypsum crystals that could
whiten the upper layers of the Dead Sea, raising its temperature and
speeding its evaporation.
As an alternative to the pipeline, a local environmental group called
EcoPeace Middle East has proposed restoring the flow of water in the
Jordan River, which has been dammed and diverted until only 10% of its
former flow reaches the Dead Sea. To do this, they argue that the
mineral industry should be charged for the Dead Sea water used to fill
evaporation ponds, which yield minerals like potash and magnesium. “We
have specific steps for what can be done, and they’re all doable, but
that means changing the status quo,” says Mira Edelstein, the Jordan
River projects coordinator for EcoPeace Middle East in Amman.
Now, a much-reduced version of the pipeline seems to be the most prominent solution: This year,
bidding began to construct a pipe that would bring briny Red Sea
wastewater from a new desalination plant in Jordan to the Dead Sea.
According to Edelstein, the flow from this pipeline won’t be enough to
stem the Dead Sea’s shrinkage, and it may be canceled because of expense
(more than $900 million). But in the meantime, researchers will keep
studying the collapsing shoreline, fine-tuning their theories to peer
into the Dead Sea’s uncertain future. “If you put together all the
possible information, you have a better vision of the situation,” Atzori
says.
*Correction, 23 September, 10:47 a.m.: The
article has been clarified to note the involvement of the Geological
Survey of Israel in the study. In addition, it has been corrected to
state that the likely addition of seawater, not freshwater, could cause
algal blooms in the Dead Sea.
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