Complex sentence: As he walks towards it, he falls into the mouth of the volcano which is ringed by detonators, which are activated by Okumura, creating a controlled volcanic eruption that traps Godzilla.
Split into simpler sentences: As he walks towards it, he falls into the mouth of the volcano which is rigged with detonators. Okumura activates the detonators, creating a controlled volcanic eruption that traps Godzilla.