This video is a real eye opener.  t's from the Texas Department of Parks and Wildlife. You'll see fire flow like a river after the break.

I'm no dummy, I knew fire spread fast, but I thought it spread fast upwards and moderately sideways. In this video the fire looks like a wave coming in. This is why you should evacuate when you're told to evacuate. Do yourself a favor and watch this video. Do your friends a favor and have them watch it too.