In 1993, USGS volcanologist Dr. Harry Dalton and his colleague, Marianne, find themselves in a life-or-death struggle to escape the violent eruption of Galeras in Colombia. Tragically, their escape takes a devastating turn when a piece of debris claim's Marianne's life. Fast forward four years, Harry is tasked by his superior, Dr. Paul Dreyfus (Charles Hallahan), to investigate unsettling seismic activities near Dante's Peak, Washington—a town uncomfortably located adjacent to a dormant stratovolcano, with eruption odds estimated at 10,000 to 1.
Upon his arrival, Harry encounters the town's mayor, Rachel Wando, along with her two children, Graham and Lauren. Dante's Peak has recently been voted the second best place to live in the USA, boasting a population of under 20,000 and on the cusp of a significant investment from Blair Industries. Rachel generously invites Harry to join her as they visit her former mother-in-law, Ruth, who resides by a lake situated at the volcano's base.
As they explore the area, signs of environmental distress start to surface; they observe dead trees and animals, even encountering two people tragically boiled to death by a hot spring. Later that evening, Paul arrives with a USGS team to set up monitoring operations for the volcano. Despite clear disturbances indicating volcanic activity, Paul dismisses Harry’s concerns, urging caution to avoid triggering unnecessary panic over false alarms. Nevertheless, Harry strives to prepare Rachel and the town for potential disaster while forging a deeper bond with her family.
The town council grows increasingly anxious over the implications for Blair's $18 million investment and the potential loss of 800 jobs. Although a week passes without incident, tension mounts when one of Harry's colleagues, Terry, suffers injuries during an earthquake and avalanche in the volcano's summit crater. Meanwhile, the rest of the USGS team prepares to depart, confident there are no immediate threats. However, Harry grows frustrated, convinced that the seismic quakes are indicative of magmatic activity rather than tectonic shifts.
His concerns prove valid when he discovers the local water supply has been poisoned with sulfur dioxide. The following morning brings a disturbing rise in seismic readings and gas levels, convincing Paul to finally allow Harry to put the town on high alert as an impending eruption looms.
As the catastrophic eruption finally strikes, chaos ensues. Harry and Rachel attempt to retrieve her children, only to find they're on a mission to rescue Ruth, who stubbornly refuses to evacuate her home. In a nerve-wracking attempt to escape, they witness Ruth's cabin being engulfed by a lava flow that also destroys their vehicles. With roadways obliterated from quakes and landslides, the five escape across the lake on a motorboat, only to find that the water has turned acidic due to the volcano's fumes, damaging their motor and corroding their vessel.
In a heroic moment, Ruth leaps into the lake to guide the boat to safety but sustains severe chemical burns, leading to her tragic demise the following morning, surrounded by her family and Harry. Meanwhile, the helicopter pilot hired by Paul to assist in the evacuation turns to a profit motive, only to crash the chopper after it ingests volcanic ash.
The heat released from the eruption melts the peak's glaciers, triggering a lahar that devastates a local dam. During a temporary pause in the eruption, Harry and the Wandos commandeer a ranger's truck to return to town where the National Guard is mobilizing for evacuations. However, disaster strikes when a bridge collapses under the weight of the lahar, tragically taking Paul and their van with it.
In a nail-biting flash of courage, Harry, along with the Wandos, navigate across molten lava, rescuing Ruth's beloved dog, Roughy, along their perilous journey. Upon arriving at the deserted town, Harry discovers their escape routes are now nonexistent. While retrieving a distress signal beacon, he learns of an imminent second, more violent eruption.
As Harry rushes back to the abandoned mine where the beacon was left, the volcano erupts spectacularly, forcing them to race against time to find safety in the mine. The aftermath is devastating, and though the USGS team believes Harry to have perished, he manages to activate the beacon despite severe injury.
Days later, Terry detects the activated beacon, prompting the dispatching of search and rescue teams. Harry and the Wandos are ultimately rescued from the mine, reuniting with Harry’s team, and airlifted to safety as the film's final scenes reveal the once-thriving town now in ruins, reduced to a caldera left in the volcano's aftermath.
