Cave Diving, Cave Exploration and Cave Mapping in Yucatan, Mexico
A bathing bird at the Zoo in Sydney

Upstream and Downstream are So Nineties!

When we talk about cave diving, we usually refer to diving upstream or downstream. Upstream and downstream refer to the commonly accepted direction of the flow of the fresh water in the cave system. Here in Mexico, that direction is from inland to the sea traveling perpendicular to the coast. That knowledge is so ingrained locally that the government includesClick to view the slide in detail. it in its planning documentation. If you take a look at the image (Click it.) of the slide, you will notice red arrows pointing to the coast. The arrows represent the government’s official position on the flow of water around/under Tulum. It is also important to note that there are two versions of the urban planning documents issued by the local government. One issued in 2005 and one in 2007. If you look closely at the 2007 map you will notice the government has included stick maps of the local cave systems. This is a promising sign, the government is starting to incorporate cave survey data.

The problem is there is no empirical evidence to support the current common belief. There is anecdotal evidence that would support those hypothesizes, however it seems it may be incorrect.

Aaron Addison giving a talk about GIS at CEAOn Friday night, Allie and I had the opportunity to go to Akumal and watch a handful of presentations given at the Centro Ecologico Akumal. There were a number of very interesting presentations, including: one on the dry caves of the area, one on the benefits of GIS, the formation of the local caves and one on the movement of water at Car Wash.

The talk about Yucatan cave hydrology and geochemistry was given by Patricia Beddows, a Research Fellow at McMaster University in Hamilton, ON, Canada. Patricia has been traveling to Mexico to study the caves for at least 10 years. Last year she and a team of volunteers performed a dye tracing experiment at Car Wash to determine the flow of the fresh water there. I believe the results are remarkable.

Before I go any further, she has so far performed one dye trace at this particular site Car Wash. Therefore, the results she shared can only be representative of the water flow conditions in the cave at that time. She mentioned that repeat dye tracing may show somewhat different results.

The experiment consisted of deploying two markers. She deployed one dye in the Cell Block section and at Cenote Luke’s Hope (Cenote Zacil Ha). Both sections are upstream or inland. The expected result was that both dyes would be detected at Cenote Carwash. However, what actually happened was quite startling. The dye that was deployed in the Cell Block section, just stayed there. It never really passed the restriction heading downstream towards the coast. So it would seem that at the time of the experiment, the water was not flowing from upstream to downstream as we all believe it does.

The dye that was released at Luke’s Hope also did something remarkable. It moved relatively quickly down to Cenote Carwash, this was expected. It also moved into the Room of Tears section, this was not expected.

It seems that the fresh water is not moving from upstream to downstream at Carwash. The new hypothesis is the water is entering the system from a perpendicular path from the North and then moving down stream and out of the system south. It is also blowing water into the Room of Tears section.

Steve Bogaerts and Dennis Weeks enjoying the talk at CEAThis is import for a couple of reasons. The first is resource planning. If the government assumes the water is moving from inland to the sea in a straight line, they will plan things like dumps and well fields accordingly. However, if the reality is the water is moving unpredictably; then there is a chance those plans will create a public hazard, such as contaminated drinking water.

The second reason it is import is, it means you and I are using the wrong terminology. There was some discussion at dinner about changing from talking about upstream and downstream to inland and coastal sides of the system. We wouldn’t want to be inaccurate when briefing our dives, right! You know how important it is to be accurate in your briefings, don’t you? So get out of the nineties and your halogen lights and into modern times, it will be Costal and Inland from now on.

Lastly, the term upstream gives the impression that the flow will be working with you to assist you in exiting. When in reality, it may be working against you as the finding suggests. For example, when exiting Room of Tears. I bet you never considered that the Room of Tears might be a siphon. A very weak siphon, but a siphon. I can think of at least one place in Nohoch where there is a strong current against you when exiting, where common knowledge would indicate there shouldn’t be water moving against you.

Naturally, you should now ask, “Why isn’t the fresh water moving the direction of the cave?” The answer is equally interesting. In the last million and a half years or so, the sea level has dropped substantially from today’s levels at least 3 times. It was during one of these low periods that the cave system was formed. No one is really sure during which low period the caves formed. Therefore, the caves were formed during a period that had significantly different geomorphic forces at work then are at work today. When the cave was formed, the water did move in the direction of the cave. It was the eroding force that formed the cave.

Today, sea levels are much higher and the caves are full of water. The movement of water beneath the ground on the Yucatan is controlled by: the tides, the macro geologic formations and hydrostatic pressure from inland. (I consider the local caves micro when compared the to entire Yucatan.) The caves we dive are just happy accidents from the ancient past that provide us with hours of enjoyment. It is my unscientific opinion that Patricia’s findings suggest the following, “where the fresh water does flow in the direction of the cave, it is a coincidence”. It is my belief that the Yucatan is too porous and large for the relatively small cave passages to have meaningful effect on the macro movement of the water.

Patricia’s presentation was a call for further research. Every year, as more caves are mapped and more research is completed, we learn more about our favorite dive sites. Sometimes new information turns our commonly accepted knowledge on its ear and forces us to consider that our world is ever more complicated and beautiful then we expect.

2 comments

1 Dr. E. Don Nelson { 08.24.08 at 7:26 pm }

Thank you for your fascinating report WOW !

You mean it is not always my bad technique !

It is so neat to hear about the extremely complex movements of the waters in the caves I have been diving. The complexities of the flow add another dimension to the mystery of thc caves. As if the solitary blind cave fish in the vastness of the room of tears wasn’t enough !

Thank you for your fascinating report. Nex time I am blown sideways when I was “Just fine” seconds before I will think of your report.

Kudos to Dr. Beddows for her fine work.

I hope as a cave dive community we can save the caves before they are destroyed by ignorance, neglect, and greed.

My vote is that the caves of Yucatan should be a World Park.

Thank you and happy cave diving.

nelsoned

2 Hans { 08.24.08 at 9:39 pm }

Nelsoned,

Thanks for reading! I am glad you found Dr. Beddow’s work interesting. I have been to Nahoch a couple of times recently and couldn’t get some of the information she gave me about the flow there. It is really more complex then I ever imagined!

Keep reading!
Hans