The Gadget was detonated – the 1st nuclear explosion – by the Manhattan Project. It was a plutonium implosion device.
At 05:29:21 (July 16, 1945) local time, the device exploded. It left a crater of radioactive glass in the desert 10 feet (3.0 m) deep and 1,100 feet (340 m) wide. At the time of detonation, the surrounding mountains were illuminated brighter than daytime for one to two seconds, and the heat was reported as being as hot as an oven at the base camp. The observed colors of the illumination ranged from purple to green and eventually to white. The roar of the shock wave took 40 seconds to reach the observers. The shock wave was felt over 100 miles (160 km) away, and the mushroom cloud reached 7.5 miles (12.1 km) in height. After the initial euphoria of witnessing the explosion had passed, test director Kenneth Bainbridge commented to Los Alamos director J. Robert Oppenheimer, Now we are all sons of bitches. Oppenheimer later stated that, while watching the test, he was reminded of a line from the Bhagavad Gita, a Hindu scripture: Now I am become Death, the destroyer of worlds.
(The Gadget was similar to Fat Man, which was dropped on Nagasaki on the 9th August that year. Little Boy, which was dropped on Hiroshima on August 6th, was a uranium gun-trigger.)
Video of the blast is all over YouTube. Here is a short one.
The best documentary I have seen on The Manhattan Project is The Day After Trinity. It is currently available on YouTube; how long that will be the case is anyone’s guess. When it was filmed, several of the scientists from The Manhattan Project were still alive for interviews.
It was later determined to be an 18-to-20 kiloton explosion. (The equivalent of 18,000 tons of TNT or more) Relatively small by modern standards. Thermonuclear – or hydrogen – bombs are measured in megatons. (The largest -Tsar Bomba of the USSR – measured 50 megatons)