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As I was growing up one of my favorite fall sports was finding bubbles of marsh gas trapped beneath the ice, poking a hold in the top and light the escaping gas. The pressure that pushed the gas out of the pencil sized hole was from the water pushing up from below. This doesn't sound like much, but it was certainly enough to make it whistle out. It was fairly common for me to come home with singed eyebrows, eyelashes and hair. I would crouch over the hole, trying to protect my match from the breeze. If the first match went out, the escaping gas frequently blew in my face, and a second match could give me a surprise haircut. These never burned me, but you could sure tell what I'd been up to!
Having grown up in Lake Minchumina I was well acquainted with the locations where you could find marsh gas pockets. Bigger ones are common in certain parts of the lake. We had been planning on getting a sample to analyze in the fall of 1996, but when I arrive at Minchumina for Christmas vacation and saw the ice conditions (read: no snow) I decided to obtain a sample of gas now, rather than waiting until next year.
By this date there was very little snow, much of which had blown off the lake (Lake Minchumina, is in geographic center of Alaska-70 miles north of Mt. McKinley). This exposed large areas of bare ice, and allowed me to find bubbles. I was a little doubtful about finding some that penetrated all the way through three or four feet of ice into the water-which was a requirement for forcing out the gas. It wouldn't hurt to try, though, so I set aside a little time to explore the possibility.
Dead plant material in Lake Minchumina has several possible sources. The most likely is logs & stumps that come down the river and eventually become so waterlogged they sink. Occasionally large patches of moss, torn loose by the river, also end up sinking in the lake. Other possible sources are weeds (not so likely in this location, due to the depth of the water) and ground vegetation (which comes down the river and washes up on the lake shore. Probably composed of grass and vegetation ground down to 1-2 mm (1/8") in size.)
Mud and silt, washed into the lake by the river, covers the lake bottom and with it the sunken organic material. Bacteria begins to decompose it, but the mud keeps it from getting any oxygen. Before very much decomposition has occurred the environment goes anaerobic. This does not prevent the bacteria from digesting the plant material, but the metabolic byproduct is methane rather than carbon dioxide. A very simplified version of the chemistry going on:
Oxygen rich environment: C+O2 => CO2
Anaerobic (depleted oxygen) environment: 2C+2H2O => CH4 + CO2
As you can see you'll get carbon dioxide in either scenario. But the longer the carbon molecule, the larger the ratio of CH4 : CO2 will be. You can use this ratio as a rough indication of the length of the carbon chains in the decomposing organics.
The results of anaerobic decomposition (CH4 and CO2) are at a lower energy level than the raw materials (2C and 2H2O). The micro-organisms live on the energy released in this reaction.
I walked to a place called Holek Spit, about 2 miles from our house. I had expected to have considerable trouble finding very many large bubbles, but it turns out I was unduly pessimistic. Within an hour I had found half a dozen holes which produce a nice gush of gas; the biggest one I estimated at 200+ liters (50 gallons). I broke them open, in the hopes that more gas would collect which I could collect the next day. I also left a few un-punctured, because I wanted to try to extract gas from the bottom.
Two days later I went back with my Dad. We took the snow machine to carry all the tools and stuff. The first bubble we tackled was one I hadn't opened the previous day. We got through the meter (3.5') of ice right next to the bubble without any trouble. I wired the hose onto the wooden rod, with about 0.5 meter (18") sticking off the bottom end, and used the wire to adjust the end of the hose so that it would curl up. We then fed the hose down through the hole and attempted to suck the marsh gas into the hose. We fiddled with it but didn't have any luck. We attempted cutting another hole a little closer but didn't find any gas in that hole either. So we went to another bubble and tried that one, which also failed.
The alternative method proved much more successful, as outlined in 'Methods'. Just for fun, after we had collected all our tools, we poked holes in few more of my previous holes and lit them. We didn't find any undisturbed bubbles that were any good (had a connection going all the way to water to force the gas out). However one of the ones I'd opened two days before burned for about a minute with a good flame (2' high, 12" in diameter).
After we'd lit all availible bubbles we started the snow machine and drove carefully home, with me carrying one jar and the other two in the bucket of water. They were icy when we got home, so I put them in the sink to thaw and dry.
I walked back over to the Holek Spit to collect a couple more samples. I cut open a previously untapped hole (to get some water). After I'd opened it up it started actively bubbling, so I filled my jar with water, turned it upside down (while still submerged) and held it over the stream of bubbles until it was mostly full. Keeping it upside down I put the lid back on. By keeping an inch of water in the bottom I kept a positive seal for my sample.
I filled the bucket half full with water and then went in search of one of the holes we'd lit previously. There had been a little snow and wind, which had filled in the cavity where the bubble was. I scooped it out and filled it with water, put my jar upside down in the 2" deep water and carefully took the lid off. Then, using my pocket knife, I poked a hole in the thin layer of ice on top. It let a little gas out, but wasn't connected to the water below, so I poked a hole through the next ice layer. This time I got a good stream of bubbles, and quickly filled my sample jar.