It is a normal morning in Los Angeles and everyone is going through the usual routine on the busy
streets. Before going to work, the new director of the city's Office of Emergency Management Mike is
making breakfast for him and his thirteen-year-old daughter Kelly, who has been having some attitude
problems because of her parents’ recent divorce. Father and daughter are supposed to be leaving
on vacation today, but suddenly, an earthquake strikes the city. It is short but quite strong,
and at the hospital, Doctor Calder has to hold onto her patient to stop him from falling off the
stretcher. Mike still decides this is an emergency and he will go to work instead of vacation,
so Kelly will stay with a babysitter. When he makes it to the office, his coworker Emmit
informs him that no serious damage was caused by the earthquake so he should go back to vacation.
However Mike takes a look himself and discovers that the water main ruptured and the gas is gone
too. Meanwhile at the park, a few construction workers are working on the Red Line Subway
extension but also betting on the magnitude of the earthquake. Suddenly they hear a noise and
are shocked to see some strange yellow gas coming out from the tunnel. They rush to help a worker
out of the tunnel and discover half of his body is covered with burns. Hearing the report, Mike goes
to the park and learns that several bodies have suffered these burns. Everyone blames it on steam,
but Mike does not believe it. He attempts to suspend the subway lines that run parallel to
where the killings occurred, but MTA Chairman Olber declines because he does not think the
trains are in any danger. Olber is so proud of his project that he even ignores the requests to pause
the railway construction. Meanwhile the bodies are brought to medical forensics to be examined,
and Calder is shocked to smell something strange about the burns of the victim which indicate this
definitely was not steam or gas. Moments later, Emmit shows up at the park too to try to get
Mike off the case, since gas leaks are not their thing, but Mike is stubborn. Breaking the rules,
Mike and his coworker Gator decide to go down into the sewers to find clues. They wander around
for a while and notice that the air is becoming hotter, making it harder to breathe because of
the fumes. Since the tunnel is right next to the subway, it shakes every time a train passes by.
When Gator looks down, he finds a bunch of burnt rats, and they realize their rubber gloves are
slowly melting as well. Suddenly scorching gases being pouring out of a fracture in the concrete
and flood the tunnel, so the duo has to run away as fast as possible not to be burnt alive. Having
found evidence, Mike orders Emmit to shut down the park. Sometime later, Olber brings Amy, a
geologist that says the whole city is geologically unstable and they should not blow up tunnels under
it. Mike brings her to the park and she uses some machines to run a few studies. The conclusion she
reaches sounds a bit crazy: she believes a volcano is fast growing beneath the city,
with lava streaming underground. Unfortunately it is still a theory and she lacks the evidence to
convince Mike, who finds the idea of lava in LA ridiculous. Meanwhile nobody notices that
the statue in the park fountain is slowly sinking. Later in the evening, Amy and her assistant Rachel
inspect the accident scene in the storm drain, where they locate a fracture in the ground that
released the gases earlier. The duo wanders the underground tunnels taking samples and looking for
an explanation when suddenly another earthquake hits the area. This one is stronger and cuts
down power in the whole city. At home, Mike rushes out of bed to find his daughter and takes her to
a safe spot. Underground, the night train driver tries to stop the vehicle, but it still crashes
against falling debris. The quake cracks a hole in the tunnel where the scientists are, and Rachel
falls, leaving her hanging off the edge. Amy tries to save her, but the smoke is getting stronger and
the tunnel is becoming hotter by the second. A burning explosion of steam hits Rachel and
burns her to death, leaving Amy in shock. When she comes out of the tunnel, she notices the fountain
water is boiling. Little by little generators are turned on in the most important buildings
in town. Mike leaves home and brings Kelly with him, thinking he can keep her safe at the office.
Suddenly huge steam geysers begin coming out from every manhole on the streets. Cars stop to wait,
but it only keeps getting worse and now there is smoke and rocks falling all over the place. Mike
watches a huge smoke curtain in shock before the little rocks are replaced by actual lava bombs,
which begin causing fires whenever they land. Some houses explode, and buildings and other structures
like traffic lights get destroyed as the falling debris causes accidents for the citizens that try
to drive away in panic. At the MTA office, Olber hears about the train stuck in the tunnels and
decides to lead a team to rescue them. Meanwhile the driver calms down the terrified passengers and
tries to get out, but the doors are stuck. Back on the streets, Calder is stuck in traffic too,
and she watches how the lava bombs hit one of the arriving fire trucks. Mike stops the car to try to
calm citizens down, but many people are already looting stores. Someone steals Amy’s equipment
while she is distracted by the fact there is ash falling everywhere. As firefighters do their best
to deal with the disaster, Mike tries to reach the office, but he stops the car again when he sees
Calder taking care of an injured person. She tells him about the fallen fire truck and Mike rushes to
try to help the firefighters out, but everyone freezes when the city begins rumbling. Suddenly
another earthquake hits the area, destroying a building that drops broken glass all over them.
Mike shockingly watches Amy’s theory come true when a freshly created volcano erupts from the
city tar pits and lava begins to flow freely down Wilshire Boulevard, incinerating everything in its
path. The lava soon begins taking down vehicles, and a terrified Kelly leaves the car as she cries
to her dad for help. A lava bomb falls near her and her pants catch on fire, so Mike runs to her
and helps her put the flames out before picking her up. Finding themselves surrounded by lava,
Mike escapes by jumping onto his car and then to a safe spot right before the lava swallows
his vehicle down. The lava then goes after the fallen fire truck and a fighter tries
to rescue his trapped coworker, but he doesn’t make it in time and the lava kills them both.
As another lava eruption causes one more huge explosion, Mike hands Kelly to Calder so she can
take her to the hospital with the other injured people. Kelly asks her father to come with him,
but once again Mike puts work first and leaves her behind. Soon helicopters full of reporters
are flying all over the area, showing the lava is slowly making its way through the main LA avenue.
People are abandoning their homes as they start to crumble, and a cute dog makes sure to grab its
bone before joining its owners. Moments later, Amy joins Mike in his efforts to help the cops
and the firefighters to organize a safe evacuation and try to control the lava. Mike wants to build a
corridor that can stop the lava from reaching the rest of LA, so everyone pushes a bus away and then
shoot the tires to use the vehicle as a wall. Then Mike and Amy try to rescue an unconscious body to
safety, but at that moment, a flaming tree falls and blocks their way. The firefighters lower their
ladder and the duo puts the body on it before hanging on the edge to get away. As the ladder
moves above the lava, the victim’s legs catch on fire, and three of them start panicking to put it
off. The movement shakes the ladder and makes it break, but luckily they fall to a safe spot
outside the lava and the firefighters immediately help. Amy is starting to think they should give
up on the city and concentrate on evacuating, but Mike keeps on planning. Soon cops, city workers,
and firefighters are grabbing jackhammers and other tools to hit the streets and try to guide
the lava away from important places. Meanwhile the lava is starting to fill the Red Line tunnels
as well while Olber leads his squad to the crashed train in search of survivors. Everyone
is unconscious and has to be dragged out of the vehicle, but at least they are safe. As
the lava comes closer, Olber notices that the train driver is still missing and returns to
find him. The driver is alive but unconscious so Ober has to pick him up to leave, shoes melting
with every step as the lava reaches the train and begins to melt it down. Feeling guilty for how he
handled the situation, Olber jumps into the lava and flings the driver at his team before he dies.
Back to Amy, she grabs a basketball from a store and puts it on the ground, where it starts to roll
on its own. This indicates an inclination on the ground that will take the lava in the direction of
a gas station. The workers continue to push cars and other vehicles to try to guide the lava away,
but it is not very efficient. Eventually a bunch of emergency trucks arrive and Mike and
Amy create a plan to erect concrete barricades at the intersection of Wilshire Boulevard and
Fairfax Avenue, forming a cul-de-sac in which to pool the lava while helicopters spray water on it
to produce a crust. Soon every person available, even a few remaining civilians, is pushing every
piece of debris available while Mike guides them with well-organized orders to keep the
barricade in the right direction. Meanwhile at the medical tents, vets are starting to save animals
too. Calder helps a few kids with their burns and asks Kelly to keep them entertained until
they find the parents. Back to the streets, the barrier is finished and the firefighters proceed
to shoot water with hoses and truck cannons. Soon helicopters also join the team to spread
more water and they manage to harden enough to make it stop. Everyone rejoices and celebrates,
assuming the eruption has stopped. However Amy still worries and enters the subway tunnel to
double-check. Using a gadget, she confirms that lava is still moving underground. She calls
Mike and explains they didn’t stop the lava, it just moved somewhere else, and she compares the
incoming eruption to the Hiroshima bomb. The lava is traveling through the Red Line subway
extension, and her calculations indicate that the main eruption will occur at the end of the line at
the Beverly Center, where the medical tents are. Mike immediately joins Amy at the end of the line
and they lower a video camera into the tunnel to observe it, only to have it incinerated by
a fast-moving flow of lava. Mike has to push Amy away before the flames blow up into the street as
well. They analyze the pace they see in the tunnel and discover that the lava will erupt at the end
of the red line in thirty minutes. After calling Emmit so he can start evacuating the medical
tents, Mike discusses their options with Amy, only to start to lose hope. Fortunately Mike sees
a building and is inspired with an idea: they can use explosives to make channels in the street that
divert the flow of lava into Ballona Creek, which would eventually flow into the Pacific Ocean.
The roadway is sloping in the opposite direction, but they can solve that by demolishing a 22-story
condominium building, which should prevent the lava from entering the city. Mike asks Amy to go
find his daughter while the team begins working on setting up the explosives. However when Amy makes
it to the victim groups, she discovers Amy is gone because she lost one of the kids and is out there
looking for him. Back to the team, they’re running all over the place because they only have twenty
minutes to get it all ready. Gator and his men are placing bombs inside the center, but at that
moment, earthquakes begin hitting the area again. The huge eruption happens sooner than expected and
destroys the street, causing everyone to run away in panic and many patients to catch on fire while
they’re being evacuated. Inside the center, one of the workers gets trapped under a core column that
the earthquake destroyed and Gator isn’t strong enough to push it away. The lava is coming closer,
but Gator refuses to leave the mission and chooses sacrifice in order to detonate the final explosive
charge. One by one the explosives begin going off, but at that moment Mike notices Kelly and
the little boy in the path of the explosions. He runs as fast as he can and pushes his daughter and
the boy down as the entire building collapses. Fortunately the plan goes perfectly and the
resulting tunnel guides the lava successfully to the ocean. While people celebrate the victory,
Amy looks around for her new friend. Suddenly a hand pops out from the pile of debris, and Mike
emerges with Kelly and the tiny child, all alive and well. The kid notices everyone is covered with
ash, making them all look the same regardless of race until rain starts to fall and washes
the ash away. Amy admits that if she had been in charge, she would have sacrificed half the city,
so she thanks Mike for teaching her not to give up. At that moment Emmit arrives with a new
emergency for Mike, but he turns it down, saying he is leaving for a vacation with his daughter.