Godzilla: How Powerful Was Godzilla’s Explosion? Fission vs Meltdown Explained

Godzilla vs. Destoroyah (1995)

In this post, we analyze the two catastrophic scenarios proposed in the film regarding Godzilla’s internal reactor meltdown. Using visual scaling, real-world geographic references, and physical models such as the Sedov–Taylor scaling law, we estimate the energy output of both the full fission detonation and the crust-melting scenario. By quantifying fireball size, expansion time, crust melting, and water vaporization, we determine just how destructive each outcome would be—and whether either could truly threaten the planet itself.

First Theory

According to estimates presented by the scientists in the film, Godzilla’s fusion would generate an explosion powerful enough to burn Earth’s atmosphere. Although the mechanism is not fully explained, the film does provide a visual representation of the potential blast size. We will therefore use that visual reference to estimate the fireball’s dimensions.

Godzilla vs. Destoroyah (1995)

Using Shikoku Island as a scale reference:

Shikoku length: 255 kilometers = 45 px

Fireball diameter: 95 px = 538 kilometers

Fireball radius: 269 kilometers

Explosion duration: 6 seconds

With these values, we apply the Sedov–Taylor scaling law:

$E = 1.2 \frac{R^5}{t^2}$

Substituting the data:

$E = 1.2 \times \frac{269,000^5}{6^2} \approx 4.6 \times 10^{25} \text{ joules}$

This corresponds to approximately 11.2 billion megatons of TNT, a value approaching the Sun’s energy output per second (~3.8 × 10²⁶ joules).

Such an energy release would be more than sufficient to devastate Earth’s surface entirely.

Second Hypothesis

After learning that the cooling operation prevented Godzilla from entering full fission mode—but did not stop his internal reactor from melting down—the film suggests a different catastrophic scenario. Instead of a global atmospheric burn, the meltdown would trigger a process capable of melting Earth’s crust once Godzilla reached temperatures of approximately 1,200 °C. Let us estimate the scale of this hypothetical explosion.

Initial Explosion in Tokyo Bay

Godzilla vs. Destoroyah (1995)

In this version, the fireball is significantly smaller. It remains confined within Tokyo Bay, covering only part of it. If we consider the distance from the coast of Chiba and Funabashi to Kawasaki, the affected diameter is approximately 30 kilometers.

The explosion reaches its maximum diameter in 0.5 seconds. Applying the Sedov–Taylor scaling law:

E = 1.2 \times \frac{15,000^5}{0.5^2} \approx 3.6 \times 10^{21} \text{ joules}

This corresponds to roughly 860,000 megatons of TNT, significantly lower than the first scenario.r.

Crust Melting Scenario

The nuclear fireball shown in the simulation appears to have a smaller core, approximately 5 km in diameter. It proceeds to melt through 40 km of Earth’s crust, and the simulation implies it could continue toward the planet’s core.

Focusing first on the crust, we model the melted region as a cylindrical column:

$V = \pi \times 2,500^2 \times 40,000 \approx 7.85 \times 10^{11} \text{ m}^3$

The crust beneath Tokyo has an average density of 2,700 kg/m³, increasing to about 3,000 kg/m³ near the upper mantle. Using the crustal value:

$M = 7.85 \times 10^{11} \times 2,700 \approx 2.12 \times 10^{15} \text{ kg}$

Melting rock requires approximately 2.65 MJ/kg, giving:

$E = 2.12 \times 10^{15} \times 2,650,000 \approx 5.6 \times 10^{21} \text{ joules}$

This equals roughly 1.3 million megatons of TNT—and this accounts only for melting the crust.

If the process extended deeper into the mantle (down to ~670 km), the additional energy required would be lower than expected, since mantle material already exists at temperatures between 900 °C and 1,200 °C, meaning it is partially molten.

Vaporization of Tokyo Bay

Another major energy component would be the vaporization of Tokyo Bay.

The inner bay has an area of 922 km² (9.22 × 10⁸ m²) and an average depth of 40 meters, resulting in a total volume of:

$3.68 \times 10^{10} \text{ m}^3$

With seawater density at 1,000 kg/m³, the total mass becomes:

$3.68 \times 10^{13} \text{ kg}$

Vaporizing water requires approximately 2.6 MJ/kg, so:

$E = 3.68 \times 10^{13} \times 2,600,000 \approx 9.5 \times 10^{19} \text{ joules}$

This equals roughly 22 million megatons of TNT. Adding this to the previous crust-melting estimate yields a combined total near 24 million megatons.

This would still cause a global catastrophe, though it remains below the extreme output estimated for the full fission scenario.

Velocity Considerations

The fission sphere takes 1 second to travel its own diameter (~5 km), implying a velocity of approximately 5 km/s.

If it were to continue traveling toward Earth’s core (a distance of ~6,370 km), it would take roughly 21 minutes (about 1,274 seconds) to reach the center—assuming constant velocity.

Conclusion

Both scenarios presented in the film lead to catastrophic outcomes, but at vastly different scales.

The full fission scenario reaches an estimated energy output of 4.6 × 10²⁵ joules, placing it near stellar-level events and easily capable of sterilizing Earth’s surface. This interpretation aligns with the claim that the atmosphere itself could ignite, making it a true extinction-level detonation.

In contrast, the meltdown scenario, while significantly weaker, remains overwhelmingly destructive. With combined estimates reaching tens of millions of megatons, it would melt Earth’s crust beneath Tokyo, vaporize large portions of Tokyo Bay, and potentially trigger long-term geological instability. Even at its lower bound, the energy involved surpasses the largest nuclear weapons ever created by many orders of magnitude.

In short, whether through uncontrolled fission or planetary meltdown, Godzilla’s internal reactor represents a force operating far beyond modern nuclear arsenals—bordering on planetary-scale devastation.

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