North Korea and the Damage From An Electromagnetic Pulse

A recent item in a non-mainstream media source sounded the alarm bells about a potential threat from  North Korea that could be used to disrupt the United States infrastructure.  

As the world is aware, North Korea is making significant strides in its effort to create a nuclear weapon.  Other than the obvious and iconic mushroom cloud and its accompanying radioactive fallout, one of the most damaging aspects of a nuclear detonation is an electromagnetic pulse or EMP.  A high-altitude nuclear detonation produces an immediate flux of gamma rays from the nuclear reactions that take place within the weapon which then produce high energy free electrons which are trapped in the Earth's magnetic field, creating an oscillating electrical current.  This current then gives rise to a radiated electromagnetic field called an electromagnetic pulse or EMP.  The EMP can cover continental-sized areas and can affect all electrical systems on land, sea and in the air.  In July 1962, the United States conducted the "Starfish Prime" nuclear test at an altitude of 400 kilometres over the Johnson Atoll in the Northern Pacific Ocean.  This bomb had a yield of approximately 1.245 megatons or roughly 100 times the size of the bomb that destroyed Hiroshima in 1945.  The Starfish Prime test temporarily altered the shape and intensity of the lower Van Allen Belt located in the inner region of the Earth's magnetosphere, resulting in an artificial aurora borealis (i.e. colloquially known as the Northern Lights) that could be seen from Hawaii to New Zealand.  Here is a photo showing the artificial aurora seen from the Starfish detonation:

Here is a photo showing Starfish Prime taken from Maui shortly after detonation:

One of the unexpected "benefits" of the Starfish experiment was the discovery that the detonation created a massive electromagnetic pulse.  The island of Oahu in Hawaii, located more than 1300 kilometres or 800 miles from the test site received a power surge that knocked out civilian and military electrical devices across the island.  Here's what Dr. Lowell Wood, an American astrophysicist, had to say about the potential impact of the electromagnetic pulse had the Starfish Prime test taken place at the Nevada test site rather than the remote Northern Pacific Ocean:

"The first American high-altitude nuclear weaponry experiments after the Soviet breaking of the nuclear test moratorium of 1958 to 1961 revealed a wealth of phenomenology of completely unprecedented - and largely completely unanticipated - character.  Most fortunately, these tests took place over Johnston Island in the mid-Pacific rather than the Nevada Test Site, or ''electromagnetic pulse'' would still be indelibly imprinted in the minds of the citizenry of the western U.S., as well as in the history books."

In case you are interested, here is a lengthy but very interesting declassified documentary about the Starfish Prime test:

As additional background, there are three components of nuclear EMP called E1, E2 and E3.  E1 is the very fast component and is very brief, however, it is very intense and can induce very high voltages in electrical conductors.  It destroys vulnerable equipment (particularly computers and communications equipment) since it causes electrical breakdown voltages to be exceeded.  In most equipment, it acts so quickly that standard lightning protectors are ineffective as protection.  E2 follows E1 and lasts from about one microsecond to one second after the beginning of the EMP.  It is similar to a very close lightning strike and, as such, is most easy to defend against.  The main damage that occurs from E2 is the fact that it immediately follows E1 which may damage the devices that could protect against E2.  E3 is a very slow pulse that lasts tens to hundreds of seconds and is similar to a geomagnetic storm caused by a massive solar flare.  This can result in damage to power line transformers and other similar equipment as was experienced in March 1989 in Quebec, Canada and parts of the Northeastern United States when a massive solar flare disrupted the power grid. 

Now, let's look briefly at an analysis on the U.S. - Korea Institute at SAIS (38 North) website which examines the odds of a nuclear EMP attack by North Korea.  The author quoted from a paper by  D. W. Hafemeister at California Polytechnic University entitled "The Basic Physics of EMP, Beam Weapons and ABM".  The author of the paper makes the following assumptions:

1.) the nuclear detonation is spherically symmetrical.

2.) the magnetic field of the Earth is not accounted for

3.) prompt gamma rays are emitted within the first 10 nanoseconds of detonation and account for 0.3 percent of the total energy of the explosion.

4.) about 0.6 percent of the prompt gamma rays produce relativistic electrons that constitute the aforementioned E1 component of the EMP.

5.) the electrical field damage threshold is 15,000 volts per metre or higher in the E1 component of the EMP.

Using the above information, one calculates that the maximum damage distance in kilometres from a nuclear explosion is roughly equal to the blast yield in kilotons.  In other words, a 20 kiloton bomb detonated at an optimum height above the earth's surface would result in a maximum EMP damage distance of 20 kilometres and a 1000 kiloton (1 megaton) bomb would have a maximum EMP damage distance of 1000 kilometres.  According to the Brookings Institute, the estimated yield of North Korea's September 2016 nuclear test was 10 kilotons.  This compares to the 15 kiloton bomb used on Hiroshima and the 20 kiloton bomb used on Nagasaki.

So, if we put all of the information in this posting together, we can see that, currently, there is little cause for alarm when it comes to the disruptive impact of an electromagnetic pulse resulting from the detonation of a North Korean nuclear device, unless it were detonated over a densely populated area like Seoul, South Korea.  That said, as North Korea's nuclear expertise evolves, the possibility of a disruptive electromagnetic pulse will increase, particularly for neighbouring Japan and South Korea.