The rumbling was in part due to the central palatial mansion getting enveloped in a burst of explosive fire. However, that was merely an appetizer to the true destructive aftermath of Toz lighting a fortress filled with oil on fire.
The sea of oil bubbled, boiled, and burned due to the fireball. The burning oil splattered all over the cavern and, after the initial explosion, devoured all the air. The explosion, followed by the vacuum of all the air burning up, put more pressure on the cave walls than they could handle.
The initial explosion had long since reduced the fortress to nothing more than burning rubble. However, an avalanche of rubble buried the fortress's remains as the surface of Pirate Haven came tumbling down on top.
The Blue Lounge headquarters disappeared in a fiery collapse, revealing the hollow ground that had served as the Blue Lounge League's last defense.
