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Mysterious Siberian Crater Is Just One of Many
New submitter Sardaukar86 sends this excerpt from a Washington Post report:
In the middle of last summer came news of a bizarre occurrence no one could explain. Seemingly out of nowhere, a massive crater appeared in one of the planet's most inhospitable lands. Early estimates said the crater, nestled in a land called "the ends of the Earth" where temperatures can sink far below zero, yawned nearly 100 feet in diameter. The saga deepened. The Siberian crater wasn't alone. There were two more, ratcheting up the tension in a drama that hit its climax as a probable explanation surfaced. Global warming had thawed the permafrost, which had caused methane trapped inside the icy ground to explode.
Now, however, researchers fear there are more craters than anyone knew — and the repercussions could be huge. Russian scientists have now spotted a total of seven craters, five of which are in the Yamal Peninsula. Two of those holes have since turned into lakes. And one giant crater is rimmed by a ring of at least 20 mini-craters, the Siberian Times reported.
Now, however, researchers fear there are more craters than anyone knew — and the repercussions could be huge. Russian scientists have now spotted a total of seven craters, five of which are in the Yamal Peninsula. Two of those holes have since turned into lakes. And one giant crater is rimmed by a ring of at least 20 mini-craters, the Siberian Times reported.
There are a series of "craters" in the U.S. as well, though much older. The Carolina bays are elliptical depressions located along the Atlantic seaboard of unknown origin. Theories of the origins being geologic or extraterrestrial impacts have come in and out of favor. Nobody really knows. (And before you say that impact craters are round regardless of the angle of impact, that's true until you get to very shallow impact angles. Then the craters end up being oval.)
You need to find out about methane clathrates. They are very roughly a chemical compound of methane and water which is solid and stable at low temperatures and moderately high pressures (as found under a few hundred meters of water or ice, for instance. When they get a bit too warm, or the pressure drops a bit they turn back into methane gas and water. One cubic meter of clathrate released almost 200 cubic meters of methane gas, which then has to go somewhere producing something like an explosion. At no point did the methane burn (it was nowhere near any free oxygen until it got to the surface, it was just a gas pressure explosion.
I think the idea is this:
You have a large volume of clathrates underneath ice or frozen soil.
As things warm, they start to break down and a reservoir of methane gas builds up
at high pressure.
Eventually the pressure reaches the point where it can push aside or lift up or whatever the ice at its weakest point
and it finds a route to the surface.
Now you have a LOT of gas rushing through some kind of hole, a little bit like an oil well blowout and the gas flow erodes the sides of the hole and throws soil or ice into the air and generally starts to make a crater.
Furthermore the escape of all this gas lowers the pressure down where the clathrates are quite suddenly, so the breakdown accelerated greatly, providing still more gas to ruch up through the hole.
So not really an explosion, perhaps more like a blowout, but still fairly violent simply because of the amount of gas and the pressure.
At no point does it combust.
Imagine a large pocket of methane suddenly bursting free under some pressure. It would only take a little spark to set it off. For example, throw some stones onto some other stones. Just two stones hitting each other would make a nice spark etc.. That would easily create some big holes.
It doesn't usually work that way. If it did, we'd have far more fires and explosions in homes that heat with gas.
When gas leaks, the vast majority of the gassed area has too high concentration of gas, and too low concentration of oxygen, to burn. Further out, it's too much air and too little gas. It is only at the "interface" between those two conditions that combustion is possible, and relatively speaking that's a miniscule volume compared to either the "air" volume or the "gas" volume at any given time.
In addition to that, if ignition does occur, usually only that small volume with the ideal mix burns, leaving (again) a volume of too-high concentration, and another too low. Explosions can alter that by chaotically mixing the gas with the surrounding air, and multiplying itself. But that seldom happens.
To sum it all up: gas fires and explosions are not very common, because conditions have to be nearly ideal at the precise spot where the ignition takes place. They happen on TV vastly more often than in real life.