Cenotes denote ancient crater?

So, we're watching NatGeo the other night (I'm nerdy enough now that I don't even hesitate to throw out the self-abbreviated names of educational TV channels). We'd DVR'd a show called "Earth: The Biography" (yeah - that nerdy. I DVR educational programs). This show is basically a fascinating collection of HD film footage of our planet and this crazy Scottsman wandering around it trying to explain how it all works. Of course, he's usually mostly right, but seldom tells the entire story. However, getting to the purpose of all of this silly exposition material, I have learned a few things that I did not already know. And you all know how much I already know, so finding a new piece of knowledge is really a treat. So, now, I will share some of this with you.

The term "Cenote" (pronounced sen-oh-tay) is typically used to describe a unique kind of limestone sinkhole that is found throughout the Yucatan peninsula in central Mexico. Many of these sinkholes are partially filled with groundwater, and are usually quite scenic and spectacular. They're one of the principal tourist draws in the Yucatan, right after Mayan ruins and white sand beaches packed with rich Americans in thongs.

Here you have a cenote AND a Mayan ruin (Chichen Itza and the Sacred Cenote). It's like a two-for one ticket to the wonders of the Yucatan!

What I did know already: I have been casually researching Cenotes for years. Not only are they beautiful, but they're full of mystery and intrigue. The Mayans considered these cave-like depressions to be holy places. Not only were they some of the only sources of dependable, fresh water in the marshy jungle, but they were also seen as gateways to the afterlife. Anthropologists have discovered gold, valuables and even human skeletons at the base of the pools, and have theorized that these were offerings made to the Gods - particularly the rain gods (Chaacs) .

Cenotes are the result of freshwater dissolving limestone along weaken fractures in the rock, creating large underground caverns (uber simple explanation, true). Since the water table can be very close to the surface, the roofs of these caverns were often fragile, and collapsed - creating the sinkhole. Many Cenotes are connected via a labyrinth of underground passages and rivers creating a massive network of open and underwater caverns that cave divers treasure. If you go to the Yucatan and you get sick of all the bootie on the beach and sweating while you climb all over the Mayan Pyramids, you can always strap scuba gear on and explore the labyrinthine world of the Cenotes. They're pretty awsome.

Diving a cenote

Oh, and there's this whole dance between fresh water and salt water, because the Cenotes are actually connected to the ocean. Fresh water, being lighter, floats on top and salt water flows below - you can see the boundary when you dive through it, evidently. Kind of like flying into Phoenix on a hot day, when you can actually taste the smog layer as you pass through it...

What I didn't know: If you map the location of the 3000 some known Cenotes, they form a distinct ring. The center point of this ring is just off the shore of the peninsula. This ring is theorized to be the remnants of the Chicxulub Crater, a massive, 180-300km in diameter, impact crater - the remnant of the event that contributed to the massive extinction at the end of the Cretaceous period (the infamous extinction of the dinosaurs). If you were watching the cool TV program, they had some pretty amazing graphics that showed the near liquefaction of the earth's crust in the vicinity of the impact - though it doesn't really explain how this might have lead to the birth of the Cenotes. There's some world-renowned expert PhD mumbling about 'instability on the crater wall' and 'fractures in the limestone layer'...but no kick ass digital graphics. I guess I have to take more geology classes before I can explain it all here, and considering the stellar results of my last return to academia, I don't see that happening any time soon.

See - cool, hu?

Adjacent cenotes in the northeastern Yucatan

The life-cycle of a cenote. Eventually they fill with debris and become dry pits filled with vegetation.


An early debris pile at the base of a younger cenote

What I learned researching this blog entry further: First, Iain Stewart, the crazy Scottsman who hosts "Earth: The Biography" is actually a scientists, not an actor. I have to give props to the folks at NatGeo for not having the series hosted by Ewan McGreggor - though I find Ewan MUCH sexier. Scientists need to have fun, too.

Iaian Stewart

Ewan McGregor (obvious difference in sex appeal)

Second: There are cenotes in the United States, as close as eastern New Mexico. Bottomless Lakes State Park boasts 9 small cenotes, which, despite the name of the park, are between 17 and 90 feet deep. They only appear bottomless because of algae growth and the steep sides of the sinkhole. Three of the lakes are stocked with Rainbow Trout, and one has shallow shores which allow for swimming and other waterside activities. They were formed by the Pecos river and it's interaction with an ancient limestone reef similar to that found not far away at Carlsbad Caverns. Unlike the Cenotes in Mexico, human sacrifice is not a ritual at the New Mexico Cenotes, which may be why the Mexican Cenotes are located in a rain forest, and the ones in NM are in the middle of a very arid region. The gods must be appeased - who's going to offer themselves up to create a whole new weather regime?

One of New Mexico's Cenotes...