He is getting destroyed by the magma in this panel. Then there's a side panel in which he appears to be boiling.
Suddenly there was a huge explosion that came from just where Kaido had been punched.
I'm not concerned with Kaido's strength. Oda needed to find a means to destroy him all at once because Kaido stated nothing else could kill him. In prior panels, he told King that Joyboy will be the following person to battle and beat him.
His life was flashing through his eyes here. The very same situation occurred to Big Mom as Law and Kidd battered her to the same magmas death.