While the initial cave-in is a significant turning point, the true climax encompasses the entire period afterwards where:
* Hope dwindles: The initial attempts at rescue fail, and the characters face the grim reality of their situation, running out of supplies and facing physical and mental challenges.
* Tensions rise: The confined space and the pressure of survival exacerbate existing conflicts and tensions between the trapped individuals. Their relationships become strained and the dynamics shift significantly.
* Desperate measures are taken: The characters are forced to make increasingly difficult and risky choices to survive, highlighting the themes of human resilience and the lengths people will go to in the face of death.
Therefore, the climax isn't a specific event, but rather a sustained period of escalating crisis and desperate struggle that pushes the characters to their limits and determines their ultimate fate. It's the cumulative effect of the deteriorating situation and the characters' reactions to it that constitute the story's true climax.