Moon is currently 384,400 km away from us. It's diameter is 3,474 km & the mass is 7.3 × 10^22 kg. So what will happen if Moon fell on Earth?

Imagine moon just stopped orbiting & started moving towards Earth. On hitting earth it will release 10^20 Gigajoules of energy, which is 4 billion times the total energy of all nuclear weapons.

The impact will melt the Earth's crust where it hits & the average surface temperature will increase from 15˚C to 735˚C. As a result, Oceans & Ice Caps will be vaporized within few minutes & lava will cover the entire earth surface.