Caving In El Malpais, Part 2: Making Measurements

Our descent into Braided Cave is the typical El Malpais cobble wobble — a precarious combination of slapstick ankle-rolling and skin-shredding scrambling over jagged globs of black, vesiculated basalt. We’re here to survey — me, a geologist with the National Park Service, and two fellow Sandia Grotto members. This staircase of doom is where it all begins.


Picture a rectangular pit 100 feet long, 60 feet wide and 30 feet deep. A large portion of its total volume is filled by a lumpy dome of geological detritus that all told must weigh thousands of tons. Mostly it’s a jumble of volcanic rocks and boulders only barely packed together, but there are thorny clogs of plant matter exploding from cracks here and there. Lichen abounds.

Even to a novice like myself, it’s clear that this is a collapse structure — a section of tunnel that’s given way. Turn back the clock and watch the mess as it reassembles in zero-g. Piece by piece, the chaotic mound becomes the roof of a tunnel once again. Fissures opened by the crowbar prying of freeze-thaw and swelling roots shrink and disappear.

There are countless miles of lava tubes slithering beneath El Malpais National Monument, and being relatively shallow, a great many have had their roofs buckle under their own mass. The “skylight” we’re doddering our way down into on this particular day is but one of an as-of-yet uncounted multitude of similar structures that pock the Monument’s 114,000-acre moonscape like as many sweat glands on a human hide.


No footfall finds solid landing on a pile as poorly-sorted and loosely-consolidated as the one we’re walking down. It’s like seesaw atop seesaw all the way to the buried floor. My wandering eye isn’t making matters any better either.

Not two steps off the lip and I’m already rubbernecking, my gaze drawn to the east end of the pit, to the dark and gaping maw of the cave entrance we’re headed towards. The view is an exquisite cross-section of the El Malpais lava fields. Aboveground, I see archipelagos of drowsy cumulus grazing and fattening in endless pastures of blue, then ponderosas and junipers swaying, then twitching grasses.

Below these is a double-layer of basalt that appears to have been forced apart by the intense pressure of a shallow lava flow. When the molten stone eventually migrated elsewhere, it left a broad but very short hanging crawlway in its wake. I say “crawlway” because you could probably slide into it a little ways provided you were willing to suffer the brutal incising of the multitude of tiny “teeth” that sagged off the white-hot ceiling as it cooled. None of our party were willing, however.

Plutonic Shores

Finally, under everything, there’s the gaping maw itself — a large semicircular aperture that seems engaged in a perpetual exhalation of plutonic shadow and cold. You can feel the outpouring of gelid air against your face several meters from the drip-line, where the Lord God hath said unto the sun and rain, “This far and no farther.”          

Suddenly, a stumble forces my attention back to the task of walking carefully. While it would be very unlikely for a spill to prove fatal, you can’t help but imagine outcomes that are worse than death. A full-frontal scab; a scrumptious mouth-full of shattered teeth; a skull indiscriminately trepanned by any of a million sinister protrusions.

How easy it is to forget that we drove for an hour on turbulent jeep trails to get here! Then there was that short but rugged hike over undulating aa and fallen trees. Wouldn’t be fun at all to reverse the journey with blood running down your face and/or a fractured ankle. Best to focus for a few more paces. Once inside, the pahoehoe floor will be flat and solid, and you’ll be able to look around to your heart’s content. Surveying is slow work too — lots of time for gandering.      


While amateur cavers across the glove are involved in all manner of archeological, biological, hydrological and otherwise scientific work; it seems that surveying is most common. And it makes sense that it would be. Mapping the world’s voids is a project that lends itself nicely to crowd-sourcing. For a couple of reasons: 

First of all, while you certainly need a good amount practice to get the techniques down, you don’t need a PhD. Nor do you need someone with a PhD to teach you how it’s done. Knowledge of survey methods passes readily from one hobby caver to the next.

The other main reason is that there are just so many caves out there — far too many for the small coterie fully-fledged, university-trained speleologists to get a handle on. The situation is analogous to one found in astronomy, where in recent years everyday web-surfers have been solicited to help categorize the zillions of galaxies astronomers have photographed over the last couple decades. It’s amazing how much work can get done if lots of people are willing to contribute a little time and energy.

The Basics Of Cave Surveying

In theory, today’s survey should be a fairly straightforward undertaking. We’ll start with a fixed point — or “station” — at the entrance directly beneath the drip-line. Since we’ve not yet fully entered the underworld, we can get precise GPS coordinates to start things off. From here on out, though, humans will be doing the work of measuring. Satellites can’t tell us jack once we cross into the twilight zone.

The rest of the effort will be iteration after iteration of the same basic steps. While the trip leader records data and punctiliously sketches plan and profile views of cave passages on graph paper, the rest of the crew will set up subsequent stations and take measurements between them.

Though some surveyors use tape, we will measure distance with a snazzy laser range-finder. Pitch and direction readings, meanwhile, will be ascertained using an analog compass and inclinometer combo. Slowly but surely, a cursory map will begin to take shape.   

Theory And Practice        

Oh, but the chasm between theory and practice is seldom crossed easily, is it? We laypeople tend to think that even the most elaborate scientific measurements are simply a matter of extending our native senses. To us electron microscopy merely makes our sense of sight a little keener. Gravity wave detectors are merely heightening our sense of touch.

Unfortunately for our neat and tidy preconception of what science is, however, this couldn’t be further from the truth. One day taking very basic measurements with rudimentary instrumentation is enough to disabuse you once and for all of the notion that observation is a trivial matter.

Take the humble compass — basically a floating stylus that by virtue of its chemical make-up aligns itself automatically with the Earth’s magnetic field. At first glance, it’s hard to imagine how such an instrument could ever be wrong.

The Humble Compass

But already we’ve run into trouble. Scientific tools are never sitting out there in the vacuum somewhere all by themselves. We can never “take the humble compass” as an object divorced from other objects, processes, people, sub-cultures and so forth. (We won’t go to Heidegger-ville right now, but we very easily could.)

No, in order to function, a compass must not only be immersed in the chaos of the natural world. It also must be woven into the insane tapestry that is human thought and behavior.

This means there are oodles of variables that could potentially be significant to getting a measurement correct. Weirdness in the environment can matter. Bodily limitations of the person reading the instrument can matter. Even our beliefs about the compass and the data we’re getting from it matter. Everything hangs together! Here’s an example from the day to illustrate what I mean.

The Right Fork

After an hour or two, we’re several stations in. We’ve surveyed the above-mentioned tunnel, safely traversed another sunny collapse pit on the other side of it, and now we find ourselves in yet another segment of tunnel — feeling quite pleased with ourselves and our survey skills, I might add.   

There is a fork in the road. To the left the passage stays large and airy. Easy to survey. At some point during the last hundred thousand years, there was a lot of lava flowing through here. You can see lines along the walls where the rivers of fire used to ooze past in all their infernal glory. Perpendicular to these, arching from the floor over the ceiling and back down and spaced every ten feet or so, are contraction cracks. More signs of post-flow cooling.   

The right fork, however, is a different story. There’s a lithified cascade that leads up to a much smaller tube we’ll have to get on our hands and knees to get through. We set a station at the fork where we’ll be able to shoot measurements down both halls and then set another on top of a flat rock sitting on the floor of the crawlway.    

The front sights appear to go well enough. I can kneel comfortably, brace myself sniper-like against a rock and see over/through the the instruments down to the next station just fine. Distance, declension and inclination, no obvious issues.


The back sights are the moment of truth, though. Shooting the opposite way down the tunnel, you can check your work, thereby injecting a dose of added rigor to the operation. Front ways and backways, the numbers should match within a (somewhat arbitrarily-determined) margin of error.

C — one of the Sandia Grotto members I came out with — in charge of this task. Owing to the difficult location of the survey station, she’s prostrate in the dust trying her darnedest to even see through the compass and inclinometer viewfinders, let alone line things up properly. She reads the numbers, we do a little math, and it turns out we’re off by quite a bit. Time to start fiddling. 

Helmets come off to make sure the headlamps attached to them don’t perturb the needle. C repositions but is still stuck on the floor. The numbers are a little closer this time, but not close enough (again, this margin is somewhat arbitrary). We try again. Two eyes looking over/through the instrument, one eye. Finally S — the sketcher, survey leader and other grotto member with us today — reminds us there’s a lot of iron in the rocks. Get too close in some places and your compass will align with these local fields instead of the Earth’s global one.

Now it’s my turn to reposition. I take a step back from the rock I’m leaning against and shoot once more. Voilá! This time we’re within our envelope of error. “Good enough,” S says abruptly. Suddenly, it’s obvious there’s a storm brewing up top. Wind swoops down and rushes through the cave. It’s followed by the sound of a sustained stampeding of thunder I’ve seldom heard. Gotta wrap up the sketch fast and book it back to the truck.

Sources Of Error

As you can see, when you’re performing a measurement, confounding variables lurk at every turn. When the numbers aren’t checking out, any number of things could be the root cause. Maybe your weary bones don’t want to lie on the floor next to the station in an optimal way. Maybe the instrument’s broken. Maybe virtual particles from the ferris rocks are leaping out into space and wrenching your compass needle 90 degrees.

Then there’s all the mind games you play with yourself that addle your interpretive skills further. “Well, maybe I’m incompetent at reading compasses; your reading is probably better.” Or, “This sure doesn’t feel like west to me.”

Never mind all the the intellectual and emotional wrangling the sketcher has to do. The constant labor of minor modification and reassessment. The unending synthesis of myriad aesthetic, utilitarian and concerns. What scale to use? What surface textures are worth including? How does one decide which of the infinitude of stones piled up in the collapse pits should be drawn in precisely and which should be depicted in a more impressionistic fashion? How much time before the lightning poses a real threat to the team?

The Craft Of Making Measurements

Whether we’re talking about vital signs or neutrino velocities or declinations, we typically say that we “take” measurements. I think this is reflective of the widespread misconception I talked about earlier — our notion that measurements are gotten trivially, like pumpkins lying on the ground in a pumpkin patch. Reach down and grab one. That’s all there is to it! 

“Making measurements,” on the other hand, seems much more appropriate. When we see an ensemble making music, we know craft is involved — creativity, discipline, practice, techne. So it is with our sizing up of reality, or at least the fragment of reality our senses are privy to. Trial and error. Endless honing and innovation.

Crawling around on our bellies in the dark until we get it right.       

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