If you actually read how Moses (the 'important guy who god spoke face to face with, and they guy who got the 10 commandments off of God) describes 'God' in the bible, it's basically the exact description of a volcano.
Seeing as Moses is held to be a prophet in all three of the big monotheistic religions (Christianity, Islam and Judaism), is it possible that the 'God' of all three of these religions was actually nothing more than a volcano?
Is it not more likely that a bunch of desert nomads come witness a volcano, and seeing as they have never seen one before they think its 'God'. One of their number is crazy enough to go up onto the volcano, where he sees all sorts of volcanic stuff that he mis-interprets as god, and seeing as he's obviously a bit crazy anyways (y'know, how many sane people would go up onto an erupting volcano?) he has a bunch of 'revelations from God' on the mountain. When he gets down, not only does this impress the hell out of the nomads, but he tells them that he spoke to 'God' in the fire and smoke.
Moses (and co.) describing 'God' as a volcano:
And the LORD went before them by day in a pillar of a cloud, to lead them the way; and by night in a pillar of fire, to give them light; to go by day and night:
And it came to pass, that in the morning watch the LORD looked unto the host of the Egyptians through the pillar of fire and of the cloud, and troubled the host of the Egyptians,
And it came to pass on the third day in the morning, that there were thunders and lightnings, and a thick cloud upon the mount, and the voice of the trumpet exceeding loud; so that all the people that was in the camp trembled.
And mount Sinai was altogether on a smoke, because the LORD descended upon it in fire: and the smoke thereof ascended as the smoke of a furnace, and the whole mount quaked greatly.
And all the people saw the thunderings, and the lightnings, and the noise of the trumpet, and the mountain smoking: and when the people saw it, they removed, and stood afar off.
And Moses went into the midst of the cloud, and gat him up into the mount: and Moses was in the mount forty days and forty nights
And you came near and stood under the mountain; and the mountain burned with fire to the middle of heaven, with darkness, clouds, and thick darkness.
The LORD talked with you face to face in the mount out of the middle of the fire.