Can someone explain what/why this is happening in this nuclear test video?

Well to answer this I'll go a little bit into the science of nuclear weapons, if you just want to know the answer, skip to the second paragraph. The most primitve form is the fision bomb, which simply splits "heavy" uranium atoms into smaller atoms (I believe Barium, but I'm not entirely sure). This fision of the atom releases and incredible amount energy. The energy can be found using einsteins equation, "E=MC^2". A fusion bomb, uses the fision reaction, to compress a small mass of hydrogen so much, that it begins to fuse into helium. This reaction releases even more energy than a fision bomb.

ANSWER: Now given what is above, the bomb releases so much energy so quickly, that it send out a shock wave of unimaginable proportions, however this pressure wave has a speed of only a few hundred miles per HOUR. the speed of light (the speed of energy such as infared, microwave, visible) travels at 186282 miles per SECOND (3.0 x 10^8 Km per second). This incredible amount of energy actually vaporizes the surfaces of objects before the pressure wave reaches the object. Thus this surface essentially explodes off the object, as it heats up and expands incredibly quickly.

Now at about 1:20 in the video you posted, the trees are seen being pushed out then being pulled back in. This effect is because when the reaction occured, and the massive pressure wave was formed, it created a huge vaccum immediatly around the detination site, which causes all of the stuff that was pushed away, to now be dragged back into the center.

I know I wrote alot, but i'm hoping I answered your question. All you really need to know is that the "black cloud" is the surface of the objects being vaporized away by the incredible amount of infared radiation released by the explosion.

Israel is a Jewish u . s . a ., and Gaza is a Muslim u . s . a .. Gaza does not elect Israel there- They HATE one yet another. the two religions have been at conflict for hundreds of years. Now, some weeks in the past, Gaza desperate to deliver a suicide bomber into Israel. This killed many human beings. Now, for as long as Israel has existed, any u . s . a . it particularly is done something to them, properly... enable's basically say Israel does not carry lower back! They bypass in with finished rigidity, and that they don't bypass away until a ingredient has been made.. fortuitously, the U.S. has spoken and pronounced that they gained't take part in it (helping Israel with their assaults). desire I helped.