A Visit to Two Gypsum Caves in the Gypsum Plain of New Mexico, South of Carlsbad
In Three Parts, Each With Multiple Pages
PART 1: Introduction
Page 1-1: General introduction to the Gypsum Plain
and its karst features
I knew there were karst features, like fallen sections of land, and sinkholes, in the Gypsum Plain to the south of Carlsbad, New Mexico. But I did not know there were gypsum caves in that same Gypsum Plain.
A river runs through it. The Gypsum Plain has a river that runs through it called the Black River, and we have followed it from beginning to end on this web-site.
I learned about the gypsum caves from a co-worker, Oba Vincent, who has created an online guide to outdoor activities that are a bit off the beaten path near Carlsbad. I recommend you click on the link and peruse his web pages if you are looking for some true adventure in the Carlsbad area.
Just be safe and don't do caves alone. It is too easy to slip and break something, even if you are experienced, and YOUR CELL PHONE WILL NOT WORK underground, no matter how many Gs you are paying for.
So let's talk about this Gypsum Plain.
Figure 1: The Delaware Basin (dark gray) with its Gypsum Plain shown in white (Castile formation) and black (Rustler formation). To the right, these formations are covered with deep layers of evaporites (mostly salt beds from evaporating sea water and occasional clay seams from ancient floods on nearby shores) protecting the gypsum below.
[Taken from K. W. Stafford, L. Rosales-Lagarde, and P. J. Boston – Castile evaporite karst potential map of the Gypsum Plain, Eddy County, New Mexico and Culberson County, Texas: A GIS methodological comparison. Journal of Cave and Karst Studies, v. 70, no. 1, p. 35–46]
Imagine a world where these gypsum layers, from a deep sea's slightly cut off from the open ocean and evaporating over a long period of time. There is enough new water coming in and going out to keep sea-salt from falling out, so only gypsum keeps piling up, layer after layer.
Then the earth beneath the sea rises slowly, very slowly, and reefs rise out of the water and stop the easy exchange of water between this now even more isolated spot, and the greater sea lies a bit farther away. There is some addition of sea water over time, but not enough to stop constant evaporation from dropping the salt in that sea water from falling out of solution (precipitating). Occasionally a flood nearby sends a thin sheet of silt and clay onto the evaporating water, and as they settle down in the brine they form clay lenses in the ever-deepening salt.
A long, long time later the land has lifted itself high enough that the system dried out and the salt is covered by wind-blown dust, and then over and over again by the flood waters that bring more silt and clay from the nearby uplands.
Now pull yourself forward in time some more and see that to the west, especially, the land is rising faster than to the east. This bends the nicely layered salts and other evaporites like gypsum up from the west, and exposes them. Weather washes away the salt rather quickly, and just to the east of the edge of the Gypsum Plain, there is a "front" along which salt is dissolving ever eastward. But very, very slowly.
Now slap this nice picture with some reality. There are hardly ever truly straight lines in nature. So the salt dissolution-front makes several bends (look at the jagged edge between white and black in the above figure). Plus, away from the front, quite a distance away, are some places where, for one reason or another, water has managed to dissolve the sea salts below, and land has fallen down.
The pages on Nash Draw on this site show such a place. That kind of land-sinking creates karst features, sunken land, sinkholes where water runs down into instead of off the land, and even caves! Yes, caves! But I didn't know there were gypsum caves in the Gypsum Plain. Now I do.
We have to remember that caves exist in several types of evaporites, salts and minerals laid down as seawater evaporates, that are less soluble than regular sea salt. Limestone is one of those evaporites that can support caves. And so is gypsum!
So, there are gypsum caves in the Gypsum Plain, and there are calcite caves in the mountains (ancient reefs) to the west of the Gypsum Plain. Carlsbad Caverns come to mind, beautiful caverns in limestone (calcite and a few other minerals including lots of gypsum) just about 12 miles west of the gypsum caves we will visit on these pages if I'll ever stop writing words.
I am sure you are asking yourself: what is the connection between these mountain caves and these plain caves?
Hydrogen sulfide is the connection. H2S, a gas that is ever evolving from the sulfur in the oil and gas that lies beneath these evaporite layers. Gas and oil deposits are protected by these layers, in fact.
Protected how? By keeping water and oxygen completely away from them and by not allowing gases that evolve to rise up through these very thick beds and escape to the atmosphere.
That is why you don't see many oil wells where the salt is gone already, where it has been dissolved away and land has collapsed: it is karst terrain. You might get lucky, of course, but chances are whatever you find is already losing its gas and slowly disappearing. But in geology everything takes a very long time. Slowly can mean tens to hundreds of thousands of years. So drill, baby drill; and good luck!
So these evaporite beds are really tight and don't let gas or water through, and pressure builds up below them as gas is generated. So if you drill below the salts you might just get a snoot full of gas that you have released from those depths below the salt layers. And that is good, it is "natural gas" and gets a good price, just like the oil associated with it gets you a good price. But along with that natural gas also comes that nasty-smelling hydrogen sulfide gas. It is dangerous stuff, but then so is natural gas. Can't breathe much of either. Luckily gas and oil people know how to separate them, but not totally, a bit of stinkiness in the natural gas is good for detecting leaks.
But before people came and drilled in below the salt and gypsum layers to suck up the gas and oil, what did nature do when the land got bent upward to the west? Hydrogen sulfide gas started to move up, along the bottom of the now slightly upturned gypsum. The gypsum also became fractured in the process, allowing some hydrogen sulfide to come up though its new fractures. And wherever the upward moving H2S gas met downward flowing water along its path, it reacted. Its sulfur met grabbed onto oxygen and a few water molecules, twisting its hydrogen off (electron exchange) and turning itself into sulfuric acid. So wherever water met gas, it made acid--and the acid ate the rock around it. Voila! Caves!
Calcium carbonate (calcite) and calcium sulfate with some attached water molecules (gypsum) were and are still very happy to dissolve in acid. Even our bodies would be (I recommend leaving it before you take an acid bath to see if it will dissolve).
So is H2S still evolving from the depth beneath the limestone formations to the west and the gypsum in the Gypsum Plain? Much, much slower than before, but sure, yeah.
Should you worry about breathing in H2S when you are in the caves of this region? The best advice is if you smell it (faint rotten-egg smell) get out of there, go back the way you came, don't dawdle.
But there is so little of it evolving now, and the air exchange in many of the open caves is so good, that you will not smell it. The local caves are quite safe.
So if you do detect that smell, and it is not your unwashed spelunking partner, why would you not try to hurry "past" the smell, and press forward? Because IF you are headed into higher concentrations you won't smell it anymore, you will just drop over dead.
That would be cave-littering. Don't do it.
Of course your remains will be a danger-marker for the next hiker. That's noble. Noble littering: a very strange concept.
OK, now we know enough to be dangerous concerning the origins of the caves in this region, but we also know enough to be a bit safer.
So let's get into some photos.
The first four photos are from the Gypsum Plain. The first photo shows that yes, we are east of the Guadalupe Mountains, as Figure 1 suggests we would be if we are still in New Mexico:
The second photo shows some vegetation that looks like it sits in a depression, a karst feature in this gypsum dominated land:
Sure enough when we get closer, we see that it is a karst depression:
So now we look northward and see the ancient reef, the Guadalupe Range, to our left, which has Carlsbad Caverns in it, and we see the Gypsum Plain stretching before us:
It is likely that this low-lying area before us is one big karst depression. Note the oil holding barrels. Someone drilled to the right of this photo, uphill, and has a pipeline with gravity drainage into these barrels. Lucky. If we follow this pipeline road over that rise in the distance, we come to a place where there are about 20 cave openings, and allegedly some 14 miles of gypsum cave tunnels. BLM (the Bureau of Land Management) manages the land with the caves, and will be happy to give you information about your visit if you visit their office in Carlsbad. In fact a BLM Ranger checked on us while we were temporarily out between spelunking adventures. Nice to be cared about.
PART 1: Introduction
Page 1-1: General introduction to the Gypsum Plain and its karst features YOU ARE HERE
Page 1-2: A look around before heading into the caves NEXT
Part 2: Cave A
Page 2-1: Moving into the cave
Page 2-2: Deeper into the cave
Page 2-3: A good place to stop and return
Part 3: Cave B
Page 3-1: Looking around before entering the cave and coming to a good place to turn around
Page 3-2: Interesting rock fabrics along the way
Page 3-3: Merging with other underground streams before the exit
The Vincent Online-Guide to Spelunking Opportunities near Carlsbad
Another set of Gypsum-Plain pages: The Black River
Carlsbad Caverns: Photos or a Movie (page has links to four movies, one is about Carlsbad Caverns, and has instructions for use)
What made this place the way it is today? Looking back at the Permian.
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