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ts center is located near the town of he Yucatán Peninsula contains a vast how effective these are at draining water to
the coast, and the distance from the coast.
I Chicxulub, after which the crater is T coastal aquifer system. The infiltrating In general, the halocline is deeper further
from the coast.
named. The crater is more than 110 miles rainwater floats on top of higher density
in diameter and 12 miles in depth, making saline water intruding from the coastal T he Yucatán Peninsula has almost no
the feature one of the largest confirmed margins. The whole aquifer is therefore rivers and only a few lakes and those
impact structures on Earth. The age of the one that is land-locked but connected to are often marshy. The widely distributed
rocks marked by the impact shows that this an ocean. Where a Cenotes, or the flooded cenotes are the only perennial source of
impact structure dates from roughly 66 cave to which it is an opening, provides potable water and have long been the prin-
million years ago, the end of the Cretaceous deep enough access into the aquifer, the cipal sources of water in much of the Yuca-
period. The impact associated with the interface between the fresh and saline tán Peninsula. The first Mayan settlements
crater is thus implicated in the Cretaceous– water may be reached. The density inter- occupied the highlands around 2,500 B.C.
Paleogene extinction event. face between the fresh and saline waters is Cenotes were a fresh water supply source
a halocline, which means a sharp change in for the Mayas for hundreds of years.
A long-term effect of the impact was salt concentration over a small change in
the creation of the sedimentary basin depth.
which “ultimately produced favorable con-
ditions for human settlement in a region T Ehe mixing of the fresh and saline water ven today numerous towns take ad-
where surface water is scarce. There is a results in a blurry swirling effect caused vantage of the fresh water that comes
ring of Cenotes bordering the Chicxukub
Crater providing the only physical evidence by refraction between the different densi- from Cenotes and the underground rivers.
of the impact. When the Cenotes and caves
are mapped it becomes clear they form a ties of fresh and saline waters. The depth of Settlors established themselves at or near
distinctive circular course through the jun-
gle and mark out the rim of a giant crater. the halocline is a function of several factors: these natural wells. Major Maya settlements
climate and specifically how much meteoric required access to adequate water supplies,
water recharges the aquifer, hydraulic con- and therefore cities, including the famous
ductivity of the host rock, distribution and Chichén Itzá, were built around these natu-
connectivity of existing cave systems and ral wells.
