In what way is the theme of altruism demonstrated in Chapter 21 when an earthquake rocks the island?

The narrator and the old man are having a discussion on the old man's boat when an earthquake hits. Once the shaking has stopped, the narrator rushes to find the old man among the rubble inside the boat. She finds that he is trapped and that it will take her some time to free him. The old man insists that a tsunami will soon follow the earthquake and he demands that she run to safety and leave him where he is. The narrator demonstrates her love for the old man and her altruistic nature when she insists on staying to free him before they both flee for their lives.