SALT FLATS - GEOGRAPHY
News: Why
are salt flats around the world covered in a similar pattern of ridges?
What's in the news?
● In
salt flats across the world, the salt on the surface forms ridges that join
together in a patchwork of pentagons and hexagons.
● These
captivating patterns have been photographed as far apart as Bolivia, Chile,
China, India (in the Rann of Kutch), Iran, Tunisia, and the U.S. These shapes
are also invariably a metre or two across.
What are Salt flats?
● A
salt flat is a natural landscape in
which a large area of flat land is covered by salt.
● Perhaps
the world’s most well-known salt flat is
the Salar de Uyuni in Bolivia.
● It
is the largest in the world of its kind, and also contains more than half of
the planet’s lithium reserves.
● A salt flat forms from a
natural water body whose recharge rate is lower than the evaporation rate.
● Over
time, all the water evaporates, leaving behind the dissolved minerals, usually
salts.
● They reflect sunlight
strongly and thus appear bright.
● The
underlying soil is highly saline,
even if the water table is shallow, the groundwater is too salty for humans to
drink.
How are these ridges formed?
● Imagine
the soil in a salt flat - there are some ridges on the top, followed by a layer
of salt, then the topmost layer of the soil, and finally the rest of the soil.
● The
groundwater in the soil is saline but the distribution of salt is not uniform.
● The salinity is highest
near the top of the soil and decreases towards the bottom.
● The
researchers found that the salt penetrated deeper into the soil exactly below
the ridges, and remained shallow under the flat areas.
● That
is, if you removed the topmost layer and looked directly down at the soil, you
would see that the salty groundwater is flowing deeper into the soil along
vertical sheets, not throughout.
Major findings:
● If the rate of salt
deposition on the surface is sufficiently high, the denser groundwater will
sink down, and the less-saline, less-dense groundwater will rise to the top.
● Over
time, there will be more saline groundwater rising up towards the surface
through the convection cells than through other parts of the soil, resulting in
the salt accumulating on the surface and forming the narrow ridges that make up
the polygons.
● The
computer model indicates that the subsurface convection is relatively
insensitive to salt chemistry, and over time, the convection columns grew to
have a stable width of 1-2 m.
Significance of this study:
● Scientists
have proposed a variety of explanations for why the surface of dried salt lakes
develops this pattern of polygonal shapes at least since the early 1960s.
● The
majority of them have either thought about dynamics above or below the surface,
but the new study demonstrates that polygons are formed when these two realms
interact.