The awesome power and energy released is difficult to wrap your head around. Think on this: a cubic meter of water weighs a ton. Now imagine taking a single cubic meter of water and lifting it, say, 100 meters in the air, accelerating it to several hundred kilometers per hour.
Now look again at that plume. How many cubic meters of water were are in it? Even being conservative I'd say it was in the millions, meaning millions of tons of water blasted upward and outward by the force of the explosion. It's terrifying. And mind you, the test shown was for a relatively small blast: about an 8 or 9 kiloton yield (the equivalent of 8-9 thousand tons of TNT), whereas big nukes are capable of 20 megatons, over a thousand times the explosive yield shown.
I'm fascinated by big bangs - from the first one, to supernovae, and all the way down to bombs we humans make in our clever and plodding attempts to kill one another. Every now and again it's good to get a solid reminder of just what these explosions are capable of.