How did Nagasaki’s terrain affect the damage caused by Fat Man?

Nagasaki’s uneven, hilly terrain played a significant role in limiting the destructive impact of the Fat Man atomic bomb, despite the weapon being more powerful than the one detonated over Hiroshima.12

While the bomb exploded with an estimated force of 21,000 tons of TNT, the city’s geography—characterized by two coastal valleys separated by a range of hills—meant that a significant portion of the urban area was shielded from the full force of the blast and thermal radiation. Because the hills acted as natural barriers, the destruction was largely confined to the Urakami Valley, leaving other parts of the city, particularly the southeastern industrial and government districts, relatively unscathed.132

In contrast, the level terrain of Hiroshima allowed for the development of a widespread firestorm, which caused damage over a much larger area. Consequently, while Fat Man was a more potent device, the topography of Nagasaki effectively reduced the total destruction of life and property compared to the devastation observed in Hiroshima.34