Hiroshima, Japan

A brief geographical perspective to mark the 75th anniversary of the atomic bombing

Thank you to Chris for sending this card to Geography Cat’s Project Postcard. Today is the 75th anniversary of the first nuclear bombing. The Genbaku (A-Bomb) Dome shown in the postcard was of the only buildings left standing after the bomb detonated, 580m above Hiroshima on Monday 6th August at 8.15am.

An area with a radius of approximately 1 mile was completely destroyed, with the exception of the Genbaku Dome, which stood 150m away from the hypocentre (the point directly below the detonation). A further 4.5 miles radius suffered fires from the blast. Somewhere between 70 000 and 80 000 people were killed at the time, that number doubling with the impact of subsequent radiation.

Three days later a larger atomic bomb was dropped on the city of Nagasaki. Although the amount of nuclear material at Nagasaki was significantly larger than Hiroshima, the death toll is estimated to be around half at between 40 000 and 80 000.

The topography (shape of the land) at Nagasaki limited the spread of radiation, as it is roughly basin-shaped around a bay, whereas Hiroshima is a flat delta plain. Subsequent fires were also less destructive at Nagasaki than Hiroshima. I can’t find the exact reason behind this but I believe there was essentially a less dense area of fuel to burn. I think this because photographs I have seen of both cities prior to the bombings show that Nagasaki was mainly single and double storey wooden buildings, whereas Hiroshima was more densely built, with a mixture of stone, brick and wooden dwellings, many three storeys and above. Therefore, there was a greater volume of material to burn, which allowed the energy of the fire to reach a fire storm with enough intensity that it sustained itself for longer.

You will notice that both cities are in the south west of Japan, there were also other potential targets, including Kokura, Kyoto and Yokohama, all in the south west. These settlements were strategic targets for military purposes, but they were also within reach of Tinian, a Pacific island 1 500 miles away which had been controlled by the Japanese until August 1944 when seized by the Allies, who then used it as a staging post for military action against Japan.

Looking at the map above, it would seem that Tokyo would also have been a target, as it is roughly the same distance from Tinian as the southwestern targets. However, the prevailing winds in Pacific are east to west. Previous bombing raids on Japan(including Tokyo) involved bombs of around 225kg, whereas Little Boy (the bomb dropped on Hiroshima) weighed 4 400kg, and Fat Man (the bomb dropped on Nagasaki) weighed 4 670kg. The fuel required to fly these against the wind would have been more than the planes could have carried.

Emperor Hirohito announced the Japanese surrender on August 15th 1945, so bringing World War II to a close. Geography Cat’s human assistant visited Hiroshima in 1997 and met survivors of the bombing at the Hiroshima Peace Memorial Museum. She heard their stories and promised them to never forget.