I did not shoot this video. In fact, I was nowhere near this event. Further, I have never seen anything even remotely approaching this in real life.
The Commander and Sergeant Major of the Battalion whose Charlie Company I am with were reportedly in this convoy, though, and I have been told that this is authentic (though I cannot verify that).
A blast this size is definitely possible; with just a whole lot of soap, oil, and nitrate, anybody can mix up as many pounds of HME (homemade explosive) as they wish. According to the Captain here in Samarra, 1,000-lb IEDs aren't necessarily out of the ordinary.
The story on this IED is that it was simply buried too deep to detonate quickly or effectively - but holy cow would that be a scary sight to see as you drive along the road here in Iraq.