Costa Rican Swamp Gas

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.

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Don and Carlos head down to the swamp, which extends as far as you can see to the right.

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.

Carlos with the machete making a trail through the swamp

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.

Don showing us where the boards aren't

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.

Slow and careful going across the grass mat covering the swamp water

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.

Guy and the great swamp crossing with a load of non water-friendly gear

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.  

Carlos and Don reach the camouflaged funnel, which rises nearly 5 feet from the water's surface

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.

Carbon dioxide gas bubbles right out of the swamp water

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.

Camera tripod at a hole cut through the swamp grass. Now you see it...

Now you don't

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.
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A carbon dioxide gas well

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!