©Anatoly Beloshchin www.tecdive.ru
If
looking at these pictures you've noted something odd it's normal.. You are
looking at pictures that are clearly taken underwater but nevertheless it seems
that a river is flowing some meters under the the divers. This is one of the
most amazing places I've seen in my life, it's in
Mexico
and it's name is Cenote Angelita. The author of this pictures is Anatoly
Beloshchin, an excellent underwater photographer whose pictures can be seen in
his website
tecdive.ru.
©Anatoly Beloshchin www.tecdive.ru
A
cenote is a
sinkhole with
exposed rocky edges containing
groundwater.
It is typically found in the
Yucatán
Peninsula and some nearby
Caribbean
islands. The term is derived from a word used by the low-land
Yucatec
Maya to refer to any location where groundwater is accessible.
©Anatoly Beloshchin
www.tecdive.ru
Looking at these pictures you clearly have the
impression that the divers are flying over an autumnal landscape. These are the
words of the photographer:
The
river illusion is due to a phenomenon called
halocline, a
cline caused by a
strong, vertical
salinity gradient within a body of
water. Because
salinity (in concert with
temperature) affects the
density of
seawater, it can
play a role in its vertical
stratification.
Increasing salinity by one kg/m
3 results in an increase of seawater
density of around 0.7 kg/m
The Yucatan Peninsula contains a vast coastal
aquifer system which is typically density-stratified
.
The infiltrating
meteoric water (i.e.,
rainwater) floats on top of higher density saline water intruding from the
coastal margins. The whole aquifer is therefore an
anchialine system (i.e.,
one that is land-locked, but connected to an ocean). Where a cenote, or the
flooded cave it is an opening to, provides deep enough access into the aquifer
then the interface between the fresh and saline water may be reached. The
density interface between the fresh and saline waters is a
halocline, which means a sharp
change in salt concentration over a small change in depth. Mixing of the fresh
and saline water results in a blurry swirling effect due to refraction between
the different density fresh and saline waters. The depth of the halocline is a
function of several factors: climate and specifically how much meteoric water
recharges the aquifer,
hydraulic conductivity of the host rock, distribution and
connectivity of existing cave systems and how effective these are at draining
water to the coast, and the distance from the coast. In general, the halocline
is deeper the further from the coast and in the Yucatan Peninsula this depth is
10 to 20 meters below the
water table at
the coast, and 50 to 100 meters below the water table in the middle of the
peninsula, with saline water underlying the whole of the peninsula.
In Cenote
Angelita as you get deeper the water turns from pure to salty; 30 meters deep
the water is pure, 60 meters deep it becomes saline. Some meters before you get
to the bottom of the cave, you see a river underneath, with trees and leaves
floating on some liquid level. However it may seem like a river, it’s not a real
river. It’s just a layer of hydrogen sulphide.
