Content Warning: This section features graphic depictions of death. The source text includes offensive portrayals of Indigenous Hawaiian people.

Geologist and director of the Hawaiian Volcano Observatory Dr. John “Mac” MacGregor acts as the protagonist of Eruption. Of all the characters, he demonstrates the most character growth throughout the novel. He transforms from a reckless, hard-headed, strictly independent actor into someone who learns to work with and trust others to solve difficult problems.

Mac is a 36-year-old white scientist from the mainland United States. The narrative introduces him giving a surfing lesson to some of the local Hawaiian boys who come from difficult backgrounds. His dedication to this shows important aspects of his character. Even though he is not a local, he has adapted to the Indigenous language and culture of Hawaii and is conscious of the importance of being respectful of their traditions. As he tells one of the boys, his favorite, Lono Akani, “this is your island, not ours” (331). This shows the sense of responsibility he feels toward others which motivates him to try and save lives during the crisis.

At the beginning of the story, the other characters see Mac as a brilliant scientist but an impulsive, hotheaded administrator.