A short walk around Lake Accotink in northern Virginia was quite enjoyable, with many gray squirrels out and about getting ready for winter.
Okay, okay, I know Sam the Eagle isn't a real eagle, and this is quite a departure for this blog, but I was asked to create this little meme today so here it is.
After studying The Cave of Death and all the carbon dioxide coming out of it, we were interested in any other places with such emissions. Turns out Carlos knew of a gassy swamp, and so we decided to check it out.
Now most times you go slopping about in a swamp you get some gas bubbles coming up around your feet as the by-products of plant decomposition are released. This is primarily methane and carbon dioxide with some hydrogen sulfide in the mix, created when plants decompose in the mostly oxygen-free zone under the swamp water.
But this swamp was quite different than anything we'd seen. First, it is just a flat spot in the middle of a pasture that looks completely unremarkable other than one small pool of open water barely visible.
But once you start to head into it, the swampy nature becomes quickly noticeable. Did you notice in the first photo that Carlos had on waders? Well he would be the only one with dry feet after this bit.
We let Carlos go first, and it didn't seem bad at all. He worked his way out into the weeds and didn't seem to be sinking in very far. Oh this wouldn't be bad at all.
So McFarlane jumps at the chance to head in next, and just about when he catches up to Carlos he takes one step and drops through the grass matt up to his knees in water. Huh? Oh, didn't you know that a long time ago Carlos had laid boards through the swamp as a trail, but stepping a little left or right and, well, kabloosh.
However, soon enough even Carlos lost the old board trail and it was slogging along trying to step on the grass hassocks and not find spots without a plant root mat. Yes, we were in fact for the most part just walking on water. The grass grew as a mat over the top and as long a we kept to the clumpy bits then we just sort of mushed along instead of sinking deep.
At some point I realized that Guy had been quiet for too long and turned around to see him bemusedly trying to navigate the place while carrying a lot of electronic equipment and camera gear that would not enjoy it if he took a misstep and went in a deep spot.
Finally, we arrived at the exact spot Carlos was trying to find. He kept telling us to look for a funnel in the middle of the swamp, which made no sense. Until we came across a giant funnel in the middle of the swamp. An upside down funnel, but a funnel nonetheless.
Apparently since Carlos was here last, the vegetation had grown such that it completely covered the funnel. And why, pray tell, is there a giant metal funnel out here? Turns out Carlos himself put it here to capture swamp gas from a fixed surface area and then measure the flow out of the top to see just how gassy this swamp was. Okay, that's pretty neat science, and a whole lot of hard work to put that thing out there.
We popped the lid off the tube at the top and could actually see the carbon dioxide gas coming out. It's clear gas, but it looks a little bit like heat waves on a very hot day. And it's pretty much pure carbon dioxide gas. But wait...
Previously I noted that swamp gas is methane, carbon dioxide and hydrogen sulfide, and now I am saying that THIS swamp gas is 100% carbon dioxide. Yes, and yes. Because this swamp is located on the flank of the Poas Volcano, in a zone where carbon dioxide is super common in the subsurface, the swamp has become a sort of gas escape spot. From what we could tell, very little gas in this swamp is from plant decomposition, while loads of it is from some effect of the nearby volcano.
Carlos chopped a hole in the grass near the funnel to show the water surface. And it was just bubbling away! This was cool.
Okay, but this is just a large flat spot in a field, we couldn't be over more than a foot or two of water, right? Carlos had more demonstration up his sleeve to show why it would be best to walk carefully. He used a tripod with one leg fully extended.
That's some deep water! And we just were walking over it on the grass mat. After this it did seem like everyone did walk ever more carefully though.
We left the swamp and Carlos told us about all the carbon dioxide in the area. It seems that there is so much of it that they drill wells for it and capture it to use in pretty much every can and bottle of beer and soft drink in all of this part of Central America. It's a lot of gas. And on our way out of the area we did get to see one of the wells, which was our last quick stop before heading for dry footwear back at Recreo Verde.
And I hate to bury this very fun video at the end here, but this is something that Guy van Rentergem put together and is worth watching. See the gassy swamp in action!
The Cave of Death is not much of a cave, so to speak, but it is a really fascinating hole in the ground nonetheless. Extending only about 10 feet into the hillside, it ends at a crack too small to continue. That is, if it were reasonable to continue for other reasons.
Located on the flank of the Poas Volcano in Costa Rica, the Cave of Death just happens to be near some very nice hot springs which have been developed into Recreo Verde. This fine place was our base camp, actually a fabulous cabin, for our work in this area.
And as for the cave, it is a bit of a tourist attraction, and probably one of the few commercial caves where one does not in fact go in the cave. Why? Good question and glad you asked. The reason for the name is fairly simple, as the cave itself is a huge emitter of nearly pure carbon dioxide. This, as one might suspect, is what could mildly be called, "bad air" and it is quite dangerous and often fatal to animals that enter the cave.
But, since carbon dioxide is heavier than air, the "bad air" is mostly along the floor, and in fact pools up at the entrance with the spillover rolling out of the cave and along the ground. How do we know this? Another good question! Guy van Rentergem invented a clever little smoker device out of an e-cigarette machine, which could be placed in specific spots to see exactly where the gases were going. As well, we used a carbon dioxide meter to determine where the gas was and in what concentrations.
Note that the signs in the photo helpfully say "toxic gas", "entry prohibited" and "don't throw trash". The last one is kinda funny, compared to the others, until you realize that any trash thrown in the cave is rather hard to retrieve since you can't just go in there and pull it out.
And just to be thorough, we tracked the gas with smoke all the way out of the protective barrier at the cave's entrance where it eventually drifts off in the breeze, while staying right along the ground.
And while Don McFarlane was taking a number of scientific measurements and recording data and just being an all around science guy...
It still baffles me as to exactly what he was doing here...
Anyway, one of the more notable features of the cave is the pool of carbon dioxide on the floor, which is remarkably stable, and nearly 100% CO2. It is just deep enough that any small animals that go in there, end up in that oxygen-free zone and quickly pass out and die. The Recreo Verde folks told us that the most common animals that die in the cave are rats, snakes and small birds. And, just looking in we could see at least one fairly recent fatality (sorry, I can't get a species from this photo).
The smoke was really useful at showing the gas movement out of the cave, but what would it do when placed under the level of the carbon dioxide pool? Man, you have all the great questions today! Turns out that the gas has a very slow-moving eddy effect going on, and after a minute or two of watching the smoke it looked like a galaxy was forming.
And just for an added attraction here at Tropicalbats.com, a video about the cave from none other than Guy van Rentergem!
So that is the Cave of Death, a carbon dioxide-emitting hole that has a penchant for killing small animals. And now I know you have one more question: Did any of us actually go in there? I end with this photo...
***Huge thanks to Recreo Verde for allowing us to study their most interesting little cave. Awesome place to stay on all accounts and really enjoyed it there.
We stayed at Recreo Verde when in this part of Costa Rica. Nice place, with hot springs as the primary draw. But we were there during the week so it was pretty quiet.
At one point it started to rain while a gentleman was cleaning the pool. See, the hot springs lead to hot water pools where you can soak and relax (get wet). But also next to them is a regular cool-water pool to jump in after all that heating up (another form of getting wet).
But now rain, apparently, is not an allowable form of getting wet. Even when waist deep in the pool one requires an umbrella to stay dry (half getting wet).
So, while Guy broke all tradition and hit the hot spring fully open to the elements (getting wet), Don was more traditional. That is, if draping bubble wrap over your head is some local form of umbrella where he comes from (being all wet in another sense).
We left the Firestone Center and drove much of the way across Costa Rica to more or less the northeast from the southwest. We ended up near the town of Aguas Zarcas on the Caribbean slope. The name Aguas Zarcas is a bit hard to translate, but it is the type of water that comes out of mineral-laden hills and turns the river rocks an orangish color. In coal mining country in the US this can be caused by acid mine drainage and is called red dog.
In this general area there are some significant travertine deposits. Travertine is just another form of calcium carbonate (see limestone) and more or less looks like cave formations but right out there on the surface. However, some of these deposits are quite thick, and here there is even a quarry mining the deposit to make fertilizer.
In the photo above, what caught our attention was the soil layer in the stratigraphy. Making a guess, and it is only a guess, the travertine was being deposited layer by layer, then a land slip covered it in soil, and then the travertine set about putting down more layers on top of the soil. This would generally be called a paleosol, but not sure that exactly applies here.
Also interesting is that the travertine deposits capture a lot of vegetation, and a variety of leaf imprints and such can be found in the rocks here.
But what does this have to do with caves? Well, travertine is soluble just like limestone, and our guide for the area, the eminent volcanologist Carlos José Ramírez Umaña, knew of at least one opening in the hillside. We took a look, and although Don looks a little lost here, he eventually crawled in and found it to be a short cave.
Nothing too much came from this, although a gorgeous lesser dog-like bat (Peropterx macrotis) was seen in there and so I had to get a quick photo. These are tiny little insectivorous bats that top the scale at a whopping four grams, or less than the weight of two dimes.
When looking for caves, it is often wise to follow the water. Our first effort at doing this came up with a waterfall and what looks like a cave under there. Turns out it was just a good place for Don to wash his feet, although really quite scenic.
Our last bit was to check out a spring near the bottom of the travertine quarry highwall. We thought this might have some potential, but the opening was far too small and although it moved a lot of water there was no airflow coming out.
And after a fine day afield...
After finishing up all our work with the bat and sea caves in the southwest of Costa Rica, we spent our last night in that region back at the Firestone Center. Not the least of the reasons was for access to a washer and dryer, as another day and you'd know we were coming before we entered the room and know we had been there long after we left.
So here are a few more photos from the Firestone. The first is an interesting scene on a leaf. This blue morpho (Morpho sp.) was patrolling a trail when I saw it and I was able to follow it until it landed. And when it landed the leaf was occupied by obvious predators of butterflies, harvestmen. But I think in this case the butterfly would be just a little on the large size for these guys to go after. Side note, the species of this butterfly is likely Morpho Menelaus, but the pattern is quite similar to Morpho didius which I do not believe to be found in Costa Rica. Anyway, when they close their wings the blue disappears and they have the brown with eye spots pattern on the ventral side of the wings.
At the Firestone Center we have a lot of peccary. They are notoriously near-sighted and even when pretty close can't seem to discern exactly what is going on unless you wave your arms or something. But they also have a reputation for being grumpy leaning toward aggressive when you get too close.
I saw these collared peccary along the trail and they just kept getting closer and even when I was moving they just kind of shook their heads and didn't run off. I took a photo and then took a little detour around them lest I get chased up a tree or something else less than heroic.
At night, I had to go into the forest to check on the mosquito trap. It was hanging in a tree down by the Rio Cacao and pretty close to the Ecology Center. On my way there, I spotted this Northern cat-eyed snake on the ground in the yard outside the Ecology Center.
They are fairly thin snakes, but when I got close it puffed itself up to probably more than twice its normal width. And while not a dangerous snake, they are rear fanged and do have a venom, but even so you can pretty much pick them up and move them out of the way if needed. Of note, this image looks a little odd since it was taken with the wide angle lens I had on my camera to photograph the mosquito trap. I was only a few inches from the snake taking the pictures, which gives it an unusual look.
And finally, one of the things we have been working on at the Firestone Center is to figure out what mosquitoes we have and which species are in which habitats. This has been a struggle as catching them in homemade traps hasn't been very successful.
Here you see the latest model of the Dynatrap, a neat little thing that was a light and a fan (sucking inward) to attract and suck in mosquitoes. The old model had to be plugged into an outlet, which unsurprisingly are not readily available out in the jungle. This model was designed to work with an external battery, and early results are quite promising that this will be our go-to mosquito catcher in the future.
Playa Ventanas is a nice little tourist beach in southwestern Costa Rica on the Pacific side. It boasts a large expanse of sandy beach and while not entirely safe it is more suitable to swimming than in some places where the currents can really be dangerous.
We stopped by as there is a fairly well-known sea cave there and wanted to check it out. But of course, we stopped and sat in the shade for a bit like normal folks do just to enjoy the place a bit.
One doesn't have to go far to find the cave, as it is pretty much just to the left of where I was standing when I took the beach photo above. Easy peasy!
And this is what you see looking at the highwall.
The hole on the left seems to be connected to the larger entrance on the right so probably all just the same cave. But why not just go in and find out? What kind of cave explorers are we anyway?
So looking into the larger opening you find that you can see right through the hill and out to the ocean. Pretty long cave, so surely Don will explore it and map it and study it until it gives up all its secrets.
It should be noted here that Don is in the cave. Technically anyway. But where is his hard hat and light? And gear? Seems a bit timid about things.
And like Sir Robin in Monty Python and the Holy Grail, He bravely ran away.
So what is going on here? Why am I asking so many questions? For an answer, here is a short video of the inside of the cave:
So, as can be seen the inside of the cave was less than tourist friendly. We were there too close to high tide to go in there, although I understand that things are quite a bit more calm at low tide, and we plan to return with better timing at some point. Anyway, there was no need for caving gear as it was clear from the start that we wouldn't be going in there.
So we hiked down the beach to the other rocky area to see if there were any more caves nearby.
We didn't find anything else enterable, but at the rocky point where the high tide prevented further shoreline exploration, Don hung out for a while. It was, overall, a pretty nice place to do so.
And finally, for those who like their photos a little Outside Magazine-ish, I goaded him into posing a shot. After this bit we headed on down the road.
After our visit to Campanario, we headed back to the Firestone Center in Baru, Costa Rica. The route took us by the sea cave where we had previously done some work, so decided to give it a bit more attention, with installation of the ammonia sampler as well. We only had to go into the chamber with the big bat colony once for this, so figured it would add a lot of data to our bat cave work without much bat disturbance and could just use red headlamp lights for the roost work.
First up is Guy with his contraption for automatic sampling of ammonia over the course of a programmable time frame. This thing worked flawlessly in what can be called less than ideal conditions.
We also did more carbon dioxide sampling at various places in the cave.
And finally, the airflow. It is one thing to have a set of numbers placed on a surveyed map which show things at this point or that point, but it is even better to have those numbers with an idea of why they are what they are. By using smoke from a vaping machine that Guy created we could essentially map the airflow patterns and speed without introducing anything harmful to the cave environment.
And, well, that is going to have to be all for now. I will finish blogging this trip after I return home as while it has been difficult at times to do so from here, after tonight it is impossible to add more. But we have been to some pretty interesting places, and still have two days to go, so look for a continuation of posts in a couple days to catch up on the final bits from the trip.
So for our last night at Campanario, Guy and I decided to just head over to the spot above the cave with the benches and watch the bat flight. This is just a really nice way to have a great wildlife experience while the sun goes down and darkness arrives. Birds stop calling and frogs start up. Day insects find a hidey hole and the night insects come out. And the bats wake up and fly out of the cave.
Okay, I gotta say here that "bats wake up" is a bit of a mystery to me. I have been in hundreds of tropical bat caves and at any point, with lights out and even before they know I'm nearby, they always seem to be awake. Cave bat colonies are never quiet and sometime really quite loud. You can turn your light off and sneak up on them from a long ways off with a dim red light and still hear them making a racket three turns of the cave passage before you get there. Makes me wonder if the bats ever actually sleep.
Okay, back to the cave. Earlier, we had seen a black hawk sitting on a downed tree with bats flying by trying to score a late evening snack. I never got a photo of it going after a bat but it clearly wanted one.
So as it was getting pretty dark, with just a hint of yellow-orange in the clouds out on the ocean horizon, I took one last Campanario Bat Cave Photo. I end this set of blog posts with a Pteronotus flying out from the cave and passing between me and the ocean. A flash went off in the night, and Guy and I headed back to the Station.
Keith Christenson - Wildlife Biologist