Dr. John "Mac" MacGregor is the 36-year-old chief geologist and director of the Hawaiian Volcano Observatory. A brilliant but sometimes hard-headed scientist, he feels most at home in the field rather than in an administrative setting, a preference that cost him his marriage. Despite being a mainlander, he respects Hawaiian culture and works to protect the island from an impending disaster.

General Mark Rivers is the chairman of the Joint Chiefs of Staff. He arrives in Hawaii to oversee the impending crisis involving both the volcano and a hidden chemical threat. Known for his imposing height and willingness to work alongside lower-ranking soldiers, he manages the competing egos of scientists and billionaires. He prioritizes public order and containment over transparency.

J. P. Brett is an arrogant billionaire tech mogul who believes his technological resources can thwart the volcanic eruption. He acts recklessly and prioritizes his ego over safety protocols. He brings private jets, water tank trucks, and drones to the crisis but frequently undermines established scientific leadership to chase dramatic media footage.

Jenny Kimura is the 32-year-old Honolulu-born lab director of the Hawaii Volcano Observatory. She serves as Mac's right-hand woman, combining technical expertise with a steady administrative hand. Dedicated to her work, she manages the observatory's operations and acts as a grounding presence amid the escalating crisis.

Rebecca Cruz is the 30-year-old director of Cruz Demolition. Brought in by the military to help place timed explosives to vent the volcano, she brings technical prowess and fearless leadership to the response team. Her energy and intelligence quickly make her an essential part of the high-stakes operation.

Oliver Cutler is a celebrity volcano hunter who prioritizes media attention over scientific caution. Brought in by local officials to provide an alternative perspective to Mac's team, he wears flashy heat-resistant suits and eagerly talks to the press, stoking public panic to elevate his own profile.

Leah Cutler is a media-obsessed volcanologist who works in tandem with her husband, Oliver. She actively seeks the spotlight, leaning into dramatic warnings about the impending eruption and utilizing J. P. Brett's resources to chase dangerous footage for public broadcast.

Rachel Sherrill is a plant biologist formerly employed at the Hilo Botanical Gardens. Following a mysterious incident in 2016 involving the blackened trees, she relocates to Portland but later returns to Hawaii seeking answers. She is determined to uncover the truth behind the military's secretive actions.

Colonel Briggs is an Army officer tasked with managing the highly classified situation at the Military Reserve on Hawaii. He serves as a critical liaison between the military and scientific teams, introducing Mac to the hidden chemical dangers stored within the mountain and coordinating the engineering response.

Henry "Tako" Takayama is the chief of the Civil Defense Agency in Hawaii. Seeing himself as a fixer, he becomes resentful when left out of the military's emergency preparations. To reassert his authority, he brings in outside celebrity volcanologists, inadvertently complicating the response efforts.

Lono Akani is a local Hawaiian teenager and an intern at the Hawaiian Volcano Observatory. Deeply connected to his island's culture and the traditions of his family, he views the volcano through both a scientific and spiritual lens, serving as a loyal mentee to Mac.

Rick Ozaki is a field technician at the observatory who helps develop the initial plans for venting the volcano. He works closely with the rest of the scientific team, analyzing satellite imagery and calculating risks associated with magma flow.

Kenny Wong is the lead programmer at the volcano observatory. He manages the data and modeling necessary to predict the lava's path, though his skills and data are later sought out by rival factions attempting to take control of the operation.

Sergeant Noa Mahoe is a soldier stationed at the Military Reserve. In his eagerness to maintain his social life, he skirts crucial decontamination protocols, inadvertently creating a biological hazard and triggering a frantic search by the military.

Imani Burgess is a reporter for the New York Times who arrives in Hawaii following tips about a chemical spill and secretive military activities. She persistently questions local authorities, attempting to pierce the veil of martial law and classified operations.

Sam Ito is a New York Times reporter working alongside Imani Burgess. He aggressively pursues leads regarding contaminated soldiers, pushing past military cordons in his attempt to uncover the true nature of the island's emergency.

Linda is Mac's ex-wife who divorced him due to his inability to settle into a stable academic life. She represents the personal cost of Mac's intense, field-oriented lifestyle, having moved frequently before finally departing with their twin sons.

Jake Rogers is an ex-navy pilot who flies helicopters over the active volcano. He routinely takes dangerous jobs from journalists and billionaires seeking exclusive footage, frequently pushing the limits of safety to satisfy his wealthy clients.

General Arthur Bennett is a retired military officer who formerly oversaw army training installations in the Pacific. Having suffered a stroke, he communicates a cryptic warning to Mac regarding an "Icetubb" and draws a radiation symbol, launching the investigation into the mountain's secrets.

Sergeant Matthew Iona is a soldier stationed at the Military Reserve. He serves as a guide and operational supervisor at the Ice Tube, overseeing the physical labor required to dig trenches and protect the classified materials from the lava flow.