Complex sentence: Several minutes to days later, once the heat dissipates enough, the steam condenses, and the pressure in the cavity has fallen below the level needed to support the overburden, the rock above the void falls into the cavity, creating a "rubble chimney".
Split into simpler sentences: Several minutes to days later, once the heat dissipates enough, the steam condenses, and the pressure in the cavity falls below the level needed to support the overburden. The rock above the void falls into the cavity, creating a "rubble chimney".