The world on Thursday marked the 70th anniversary of the atomic bombing of Hiroshima on Aug. 6, 1945, the first of two nuclear attacks carried out by the United States against Japan in the final days of World War II. According to an estimate released by the city of Hiroshima, more than 192,000 people were killed by the blast or died later from causes related to the bombing.
Thinking about the staggering scale of destruction caused by the 15-kiloton uranium bomb, code-named "Little Boy," that was dropped on Hiroshima naturally raises a question: what if it happened here? Thanks to a site called NukeMap, created by nuclear historian Alex Wellerstein at the Stevens Institute of Technology, we can get an idea of what it would look like if the same bomb were dropped on Minneapolis.
The above map shows a range of effects that would result from the blast if a "Little Boy"-type bomb were dropped on the Star Tribune newsroom in downtown Minneapolis. You can click the image to see a larger version, or view it on the NukeMap site. The innermost yellow ring shows the fireball radius, which at 200 meters would engulf at least part of the Hennepin County Government Center.
The next ring shows the air blast radius at 20 psi, which according to Wellerstein is powerful enough to severely damage or demolish heavy concrete buildings. The fatality rate in this zone would approach 100 percent. This would include Minneapolis City Hall.
The green ring, with a radius of 1.31 km, shows the area in which inhabitants would receive a dose of radiation of at least 500 rem. Without medical treatment, the mortality rate in this circle would be between 50 percent and 90 percent from the acute effects of the radiation alone, according to Wellerstein. It could take anywhere from several hours to several weeks to die.
In the outermost orange ring, with a radius of 2.21 km, victims could expect third degree burns throughout their skin layers. Somewhat fortunately for these poor souls, this would often be painless because the heat would destroy pain nerves. Read more about this map here.
But what about Saint Paul? For a second example, we decided to use the more powerful, 20-kiloton plutonium bomb, dubbed "Fat Man," that was dropped on Nagasaki, Japan, three days after the Hiroshima attack.
Here we can see what would happen if "Fat Man" were dropped on the Minnesota capitol. A number of local landmarks, including the Cathedral of St. Paul, the Xcel Energy Center, the Minnesota Children's Museum and CHS Field all fall within the green radiation ring where the mortality rate would be extreme. Read more about this map here.
Finally, we decided to take a look at the possible effects of the largest bomb ever designed, the former USSR's hydrogen "Tsar Bomba," which would have exploded with the force of 100 megatons (that's 100 million tons) of TNT. A 50-megaton version of the bomb, known as Big Ivan, was detonated in a 1961 test.
Here's a video of that explosion:
An initial design for a bomb twice as powerful was scaled back because of the extreme nuclear fallout that would have resulted and the inability of the airplane delivering the bomb to escape the blast.
Here's what the map would look like if the original "Tsar Bomba," as designed, were successfully dropped on Minneapolis.
You can read about this map here, but suffice it to say it's a good thing the cold war is over.