North Korea: What would happen if rogue state detonated a hydrogen bomb underwater?

The ocean would be devastated and low-orbiting satellites would cease to function.

Planes would literally fall out of the sky as technology stopped working and huge waves carrying radiation rushed ashore.

Marine life in the immediate area would be killed and thousands of other animals and humans would remain at risk for long periods of time.

Radiation would disperse, flowing into an unknown number of waterways.

They are among just some of the terrifying prospects the world faces if North Korea followed through with its threat to carry out a hydrogen bomb test in the Pacific.

North Korea's Foreign Minister Ri Yong-ho told reporters in New York his country may consider doing just that in retaliation to tough UN sanctions.

Ri said the potential test of "the most powerful detonation of an H-bomb" would be one possible "highest-level" action against the US.

"It could be the most powerful detonation of a hydrogen bomb in the Pacific," Ri told Yonhap. "We have no idea about what actions could be taken, as it will be ordered by leader Kim Jong-un."

While the thought of North Korea conducting such a test is frightening, analysts offered differing views of the fallout from such an event.

Most agree the result would not be pretty. Oliver Buhler, a professor of applied mathematics at New York University, told Motherboard there would be waves, and big ones at that.

"An underwater explosion or an above ground explosion would clearly create a bunch of waves, strong waves," he said.

There would also be a shockwave which would radiate outwards and carry "upwards of 140 kilotons of energy".

Buhler said the waves would disperse and the bomb would act more as a storm arriving over a period of time.

Motherboard also reveals how radiation fallout could continue for years after the blast occurred.

Kim Jong-un has been engaged in a war of words with US President Donald Trump. Photo / AP

In an analysis for The Interpreter, Australian space analyst and writer Dr Morris Jones paints an equally horrifying picture of what would happen post blast.

Morris writes that the physical blast and electromagnetic effects would be catastrophic and, if the blast occurred without warning, things could get even worse.

Electronics on planes would fail, causing them to fall from the sky while satellites in low-Earth orbit would be impacted.

That's even before we consider the effects on ocean and marine life which would be hugely serious.

Morris suggests a launch in the Pacific Ocean would having nothing to do Kim's war of words with Donald Trump.

He says Pyongyang could carry out such a test because its current nuclear testing site is reaching its limit.

He points out while Punggye-ri's tunnels have contained previous blasts, they weren't strong enough to contain the latest one.

The next step, he writes, is to produce an even bigger bang. North Korea simply doesn't have the space or geography to accommodate it.

But that's a position that other experts dispute. Graduate research assistant at the Middlebury Institute of International Studies told news.com.au there is only one reason North Korea would detonate in the Pacific.

"The reason ... would have nothing to do with Punngye-ri per se; they could easily find another mountain," he said.

"The DPRK would test out over the Pacific out of a desire to conduct an 'end-to-end' test of its nuclear weapons system and prove that the warhead will explode in the target area after the stresses of a trip out of the atmosphere and back."

He said the most significant aspect of testing in the Pacific is the fact that "the rocket would have to fly over Japan with a live nuclear warhead.

"Imagine the consequences of it tumbling onto Japanese territory."

North Korea has conducted six nuclear tests, all of which have taken place at its Punggye-ri site in the country's northeast.

The latest, which took place on September 3, was considered to be its most powerful yet.
Monitoring groups estimate that the test had a yield of 259 kilotons, which is 16 times the size of the bomb that destroyed Hiroshima in 1945.

Hydrogen bombs are thermonuclear weapons more powerful than ordinary fission-based atomic bombs. H-bombs use a nuclear blast to generate the intensen temperatures required for fusion to take place.

Morris' warning comes after Geophysicist Wen Lianxing and his team at the University of Science and Technology of China warned the mountain beneath the testing site could be on the verge of collapse.

Wang told the South China Morning Post it was a major environmental disaster in the making.

Satellite imagery revealed by the Washington-based 38 North monitoring project also shows the blast caused numerous landslides around the Punggye-ri test site.

However research Associate at California's James Martin Centre for Nonproliferation Studies Shea Cotton told news.com.au he wasn't convinced about the testing limits at Punggye-ri.

He said colleagues conducted an analysis which concluded that it could easily contain tests in the hundreds of kilotons if they stuck to their current layout.

"I think if North Korea decided to do an atmospheric test out over the Pacific it would be because of political reasons, not technical," he said.