How North Korea’s hydrogen bomb works, why it’s ten times more powerful than Hiroshima and what would happen if Kim’s missile hits London
NORTH Korea claims to have successfully tested a massive hydrogen bomb in a move which has literally sent shock waves across the world.
More than 130 quake stations recorded tremors from the mega-blast, which after 20 minutes had already reached Argentina more than 12,000 miles away.
Based on the strength of the tremors - equivalent to a magnitude 6.3 earthquake - nuclear weapons specialists put the yield of the bomb at up to 100 kilotons.
That is roughly 10 times more powerful than any of the previous nuclear bombs tested by the North Korean military.
If Kim Jong-un's scientists have built a 100 kiloton H-bomb, its explosive power would dwarf that of the US nukes dropped on Japan in 1945 - which exploded with an energy of 10 to 20 kilotons.
As well as its more obvious destructive power, a hydrogen bomb can also be detonated in the atmosphere sparking a massive electromagnetic pulse knocking out electrical supplies.
North Korea’s state media claimed its underground test of the H-bomb - reportedly capable of being loaded into an ICBM - is a major "game changer" in its escalating war of words with the US.
If it was targeted at most major cities, hundreds of thousands would die and many more would be horrifically injured.
Those more than 2.5 miles away from the explosion will still suffer horror third degree burns as seen after the blasts in Japan.
Why did North Korea test its H-bomb underground?
Nuclear devices are often tested underground to prevent radioactive material released in the explosion reaching the surface and contaminating the environment.
This method also ensures a degree of secrecy.
The release of radiation from an underground nuclear explosion - an effect known as "venting" - would give away clues to the technical composition and size of a country's device.
How exactly does the underground test work?
A test site is carefully geologically surveyed to ensure suitability - usually in a place well away from population centres.
The nuclear device is placed into a drilled hole or tunnel usually between 200-800m (650-2,600ft) below the surface, and several metres wide.
A lead-lined canister containing monitoring equipment is lowered into the shaft above the chamber.
The hole is then plugged with gravel, sand, gypsum and other fine materials to contain the explosion and fallout underground.
What happens once the device is ready for testing?
The bomb is remotely detonated from a surface control bunker.
The nuclear explosion vaporises subterranean rock, creating an underground chamber filled with superheated radioactive gas.
As this cools, a pool of molten rock collects at the bottom of the chamber.
Minutes or hours after the blast, as the pressure falls, the chamber collapses in on itself causing subsidence and a crater to appear on the surface.
Tremors from the underground blast can be registered thousands of miles away.
When did the first underground tests take place?
The first underground test took place in 1951; further tests provided information that eventually led to the signing of the Limited Test Ban Treaty in 1963, which banned all nuclear tests except for those performed underground.
From then until the signing of the updated Comprehensive Ban Treaty in 1996, most nuclear tests were performed underground, in order to prevent fallout from entering into the atmosphere.
North Korea's latest blast is believed to be the sixth nuclear test carried out at Punggye-ri - the previous ones were carried out in 2006, 2009 and 2013 and 2016.