I only learned about cenotes a mere weeks before I set foot on that magical country called México – what they are is quickly explained, but there is a much more profound story behind them than that they make for spectacular swimming pools or even that the ancient Maya apparently included them in sacrificial ceremonies.
Cenotes are natural sinkholes and they are the result of collapsing limestone ceilings – relatively soft rock from right below the earth’s surface. There are innumerable examples of sudden sinkhole breakaways all over the planet and even though that does sound like adventurous, it can turn out quite catastrophic in urban areas.
One such example was the 2007 sinkhole in Guatemala: Here, a 100m deep sinkhole was formed in the capital city’s northeast, in the middle of a poor neighbourhood; 5 people lost their lives and about a thousand needed to be evacuated.
Now, in the Yucatan Peninsula there are about 6,000 sinkholes (or cenotes) of varying sizes – most are reasonably small, but some are large enough to serve as a decent pool (and a favorite tourist attraction). Cenotes connect the planet’s surface with underground water bodies and that means mostly very clean fresh water. This was especially important for the ancient Maya since there are almost no rivers or lakes located on the peninsula.
So what is so interesting about the cenotes in that specific region? The Yucatan Peninsula is most famous among geologists for the location of the Chicxulub crater that was formed by the impact of either an asteroid or comet about 66 million years ago. That impact was a dramatic one and most likely responsible for a mass extinction including the disappearance of non-avian dinosaurs (today’s birds are the descendants of flying dinosaurs) which gave rise to populations of small possibly mouse-like mammals – our ancestors. However, it is estimated that about 75 % of all flora and fauna species then present on the planet became extinct.
The following map of the crater impact structure reveals a striking concentration of cenotes around the crater rim (represented by white dots; the white line shows the coastline). These sinkholes can not only be as deep as up to 100 metres, they are actually connected by a vast network of underwater cave structures. And these were most likely formed by the asteroid’s (or comet’s) tremendous impact that would change the face and shape of the planet until today. Keep all this in mind next time you jump into one of those wonderfully refreshing natural wonders!