[Dog Gone]

I suppose that's possible, although this could be pretty easily ruled in or out by any competent geologist. It would require a shallow high pressure reservoir (unlikely right there) which is suddenly fractured (presumably by earthquake) with an enormous release to the surface of a couple hundred billion cubic feet of methane.

Presumably there is a campfire or other ignition source in the immediate vicinity.

The odds of this being the culprit behind Tunguska are very remote.

[COB1]

"The odds of this being the culprit behind Tunguska are very remote."

I agree, dog.
If we were talking about methane collecting in a valley from a shallow gas bearing sand, then suddenly exploding due to static electricity, I could buy that.
But I can't buy gas collecting in an area the size of Rhode Island!

The second possibilty is equally remote:
A deep high pressure sand is somehow suddenly relieved of it's overburden pressure and blows out.
The blowing out of the amount of gas necessary for that kind of explosion in that short of a time period is an unrealistic scenario.

[aruanan]

It would require a shallow high pressure reservoir (unlikely right there) which is suddenly fractured (presumably by earthquake) with an enormous release to the surface of a couple hundred billion cubic feet of methane.

And yet gaseous explosions are quite often associated with earthquakes. Also, some earthquakes may themselves be due to structural failure of rock and the release of vast quantities of methane, with or without subsequent ignition. Although it was believed previously that the fires of the San Francisco earthquake were due to broken gas mains, there is evidence that they were not due entirely to this.

In addition, methane hydrates are found not only underwater but in the tundra. A sufficiently large atmospheric blast due, say, to a chunk of comet, could provide enough pressure to destabilize large amounts of hydrate resulting in a near instantaneous release and subsequent ignition of the gas.