Look at the blades coning, he was way overweight. When he got out of ground effect he lost whatever lift margin he had and the aircraft literally fell into the water. Once in the water he tried to get some forward speed to generate lift but the combined weight along with the drag of the water pulled him under. Overloaded CH47s use running lift offs to achieve flight when they can't generate enough lift to take off straight out from a hover. His best bet would have been to water taxi back to land but being a pilot he thought that he had this, it was fortunate that the crew and passengers were fished out... unfortunate that he didn't survive. The ultimate price for hubris.

he landed in the salt water which is very bad for jet engines and robs power and he may have been heavy but he should have pulled it into a 40ft hover (if he had enough power)and then slowly trans to forward flight

By the way that the rotors are bending up, he seems to be low on rotational speed. It looks like he then tried to take off again and nosed over. Bummer !

Engine did NOT explode - main rotor struck water - tail rotor energy was blocked at transmission - tail boom then over-torqued & exploded - watch tail boom CAREFULLY during sequence! Anytime you touch a main rotor on anything, THIS HAPPENS!