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I was sitting around the camp fire and there was a periodic sound of cracking and pieces of the burning wood flew off. My question is what is the mechanism for the cracking of the wood? I was thinking it was a pocket of air in the wood or something, but that still doesn't explain why the piece of wood flew well over a meter high. Could this be a chemical reaction causing this?

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up vote 14 down vote accepted

Wet wood crackles. Dry wood does not.

Water in the wood boils. The steam builds up pressure because it is trapped inside. The wood explodes, releasing the steam and flying pieces.

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+1 Crackle often goes together with a continuous hiss and sometimes steam jets from the ends of logs and sticks. – WetSavannaAnimal aka Rod Vance Apr 1 '14 at 4:59
Also, waxy wood (pardon if this isn't the correct term in English) crackles more, for the same reasons as wet wood. – Nit Apr 1 '14 at 11:33
Thanks all who answer! So not air pockets, more like water pockets. Makes sense. Also, explains why it was so tough getting the fire started! Thanks again! – jerk_dadt Apr 2 '14 at 6:06

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