Imagine a 150-kiloton nuclear bomb exploded in the city closest to you.

Do you know how the city, its surrounding region, and its inhabitants would be affected? If you can't think of much more than "a lot of people would die," you're not alone.

"We live in a world where nuclear weapons issues are on the front pages of our newspapers on a regular basis, yet most people still have a very bad sense of what an exploding nuclear weapon can actually do," Alex Wellerstein, a historian of science at Stevens Institute of Technology, wrote on his website,

To help the world understand what might happen if a nuclear weapon exploded, Wellerstein created an interactive browser app called Nukemap.

Nukemap's projection of the impact of a San Francisco ground detonation of a nuke like the one North Korea recently tested. (Image Nukemap)

Casualties and radioactive-fallout zones

When we switched the height to "surface burst," a very different picture emerged: The thermal and air-blast zones shrank, but the fireball nearly doubled in area, and the radiation zone nearly tripled.

We also enabled the new radioactive-fallout settings based on local weather. And to see the human effects, we ticked the "casualties" option, too.

Luckily, local winds in this hypothetical scenario were moving west-southwest, blowing most radioactive fallout into the Pacific Ocean. If a person were to stand outside in a 100-rad-per-hour zone for four hours, they would get 400 rads of radiation exposure, which is enough to kill 50% of people by acute radiation syndrome.

According to Nukemap's casualty estimator, however, this blast would still kill about 130,000 people and injure 280,000 over the next 24 hours. The tool says this does not include radioactive-fallout effects, among other caveats.

"Modeling casualties from a nuclear attack is difficult," it says. "These numbers should be seen as evocative, not definitive."

Google Earth's view

We were eager to try the export feature, but it appears to need some work.

For example, the fallout zone appeared in an area different from the in-browser calculation — almost due south of San Francisco, instead of west-southwest.

But it was still useful — in a gut-wrenching way — to see the size of a nuclear fireball (the yellow half-dome in the image below) in 3D as it related to a major city, engulfing entire neighborhoods.

You can create your own nuclear-blast scenario and explore Nukemap 2.5's options here.

Wellerstein and others at Stevens Institute of Technology — based in Hoboken, New Jersey — are working on a related project, called Reinventing Civil Defense, which aims to "develop new communication strategies regarding nuclear risk that have high potential to resonate with a public audience." The project was awarded a $500,000 grant and is expected to debut in 2019.