blue marble adventure

#2:  Dante’s Peak

Look Mom, a pyroclastic flow!

Geologic Sin Meter:  Volcanoriffic


This rating system seems to be getting more stupid and vague with every post, so let’s just say that this rating means that this movie is actually pretty cool and relatively scientifically accurate (aside from a few hilariously foolish gaffs)

Movie Background:


This is mid-90’s geological disaster movie at its finest.  A large, dormant volcano in the Pacific Northwest is showing signs of coming back to life, and will threaten the summer tourism activities of a small Washington State town.  Mayor Rachel Wando (Linda Hamilton) has a town that has just been voted “the second most desirable place to live in America”; quite the distinction.  However, when volcanologist Dr. Harry Dalton (Pierce Brosnan) arrives at the behest of his USGS superiors to check out unusual seismic activity, that idyllic moniker is threatened.  


To add some spice to the mix, the first scene in the movie (spoiler alert) shows Dr. Dalton and his girlfriend studying a volcano in Colombia.  She is tragically killed as they try to escape an eruption, which may explain Dr. Dalton’s anxiety and caution regarding this new threat and the evacuation of the small town.


Not unexpectedly, a romantic bond forms between Mayor Wando and Dr. Dalton, and it is left to them to warn the townspeople, save lives, and outrun an erupting volcano with two kids and a stubborn grandma/mother-in-law in tow.

Geology Background:


The town depicted in this movie is in the Northern Cascades of Washington State.  The Cascades are a chain of volcanically-active mountains that run from northern California through Washington into Canada and include Mt. Rainier, Mt. Hood, Mt. Lassen. Mt. Shasta, and of course most famously (or infamously) Mt. St. Helen’s that erupted in 1980.

General Map of the Cascades and its volcanoes. (Courtesy natural history.si.net)

The best thing to do here is start with the basics.  What is a volcano?  Well, a volcano can be counted as any landform that is capable of extruding lava from the mantle onto the Earth’s surface.  This lava, which is called magma when it is under the surface, finds cracks and spaces in the lithosphere (crust) from which to escape, and upon these cracks is where the volcanoes are typically found.

They come in many shapes and sizes, and can be found all over the world in both active and extinct forms.  The most famous volcanoes are the Hawaiian Island Chain, Mt. Fuji, Mt. St. Helens, The Yellowstone Caldera, Mt. Pinatubo, Krakatoa, and Mt. Vesuvius.  The Cascades are a chain of mountains that are known as composite or stratovolcanoes.  Stratovolcanoes are the stereotypical image that one conjures up when thinking about what a volcano looks like.

This shows the varying forms and types of volcanoes found in the world (Courtesy schoolworkhelper.net)

They are generally tall in elevation, and have a distinct cone shoes with relatively steep sides.  This is due to their propensity to extrude more viscous lava that builds a tall cone, then explodes the top off.  This is in contrast to shield volcanoes that extrude less viscous lava that flows outward, creating a large dome-like structure.

The Cascades are the product of subduction, where the Juan de Fuca and Gorda plates are moving southeast and under (subducting) the North American plate which is moving to the northwest.  This tectonic action is the perfect setting for a north-south trending chain of active stratovolcanoes that explode from time to time, such as the Cascade Range.  

Simple rendering of a subduction zone.  As tectonic plates slide under and

over each other, they create pressure and build volcanically-active mountains (Courtesy livescience.com)

The mountain range is but a small part of the larger “Ring of Fire”, which is the 5,000 mile ring of active volcanoes that follow the Pacific tectonic plate as it transforms and subducts other tectonic plates circumventing the Pacific Ocean.  Roughly 85% of the world’s volcanic activity happens along this margin, and it has produced some of the largest eruptions and earthquakes in modern history including the explosion of Mt. Pinatubo in 1974, and the Japan earthquake and tsunami of 2011 that registered as a 9.0 on the Moment Magnitude Scale.  

Map of the famed Ring of Fire, the chain of active volcanism

at the margins of the Pacific tectonic plate (Courtesy livescience.com)

Geologic Sin QnA:


Could a dormant volcano “wake up”?


Absolutely.  The activity of volcanoes fall into two categories, active and extinct.  If a volcano has erupted within the last 10,000 years, it is considered active, and when it is not actively erupting it is considered dormant.  Also, if a volcano shows sigs of active volcanism (i.e. geysers, fumaroles, hot springs, mud pots, gassing, etc), it is considered active even if it has not erupted in more than 10,000 years.  Hood, Shasta, Rainier, and even now Mt. St. Helen’s are all examples of dormant volcanoes.  As we saw in 1980 when Mt. St. Helen’s erupted, a dormant volcano can quickly and violently spring back to life.


The real question here is why a town is built in the shadow of an active volcano?  The townsfolk seem to be aware, as one quips “yeah, just like Pompeii” in response to Dr. Dalton commenting on the cozy mountain town feel (Mt. Vesuvius erupted in 79 AD, wiping out the village of Pompeii and killing 16,000 people, many of whom were entombed in various living poses by the pyroclastic flow).  Hmmmm…


Is the eruption portrayed in the movie accurate?


There are several questions encased in this question.  Are the signs before the eruption accurate?  Is the timeline accurate?  Are the effects of the eruption accurate?  


The simple answer here is that yes, the eruption itself and the general ideas of the events leading put to it are an accurate depiction of a stratovolcanic eruption.  Although volcanoes are very unpredictable as to when or if they might erupt, they rarely erupt without any signals.  These signals are typically increased gas flows, increased seismic activity up to and including earthquakes, acidification of nearby bodies of water, rising temperatures in those bodies of water, small-scale eruptions, small lava flows, etc.  



The eruption itself, despite one flaw, is visually accurate and the damage that results is more than true to life.  The flaw is that the audience sees fast-flowing lava (the protagonists actually drive over it) extruding from a vent mid-mountain.  Stratovolcanic lavas are typically andesitic (intermediate) or rhyolitic (felsic) in composition, meaning that they have higher relative silicon oxide content.  SiO2 tends to make lava more viscous, meaning that it is more resistant to flow.  


This is actually one of the main drivers behind a stratovolcanic eruption.  As pressure builds, a liquid magma that is more resistant to flow is likely to explode more violently.  This is in stark contrast to a basaltic lava eruption, which will flow quickly and without much resistance.  The Hawaiian volcano Mauna Loa, which has been steadily erupting since 1984, erupts fast-flowing basaltic lava in a non-explosive fashion.  Bottom line here: large stratovolcanic eruptions with lahars and pyroclastic flows are almost never seen in concert with flowing lavas as they are depicted in the movie.  


Other than that flaw, everything else is geologically accurate including the eruption plume cloud, the pyroclastic flow, the lahar (volcanic mud flow) resulting from melted snow on the mountain, the earthquakes, the suddenness of the eruption, and the resulting devastation of the quaint mountain town.

Could a Jeep drive over a lava flow?


Um, no.  First, please see the previous question as to why rapidly free-flowing lava would not be seen in this type of eruption.  Second, even if there was flowing lava extruding during this eruption, the notion that a car could drive across it with minimal damage (popped tires) is flatly ridiculous.  Extruding lava can reach temperatures in excess of 2000F, which is not only enough to burn and melt the tires, but is frankly hot enough to melt the entire vehicle, which would likely just simply burst into flames.

Would a lake near the volcano turn highly acidic?


Yes.  The pH levels in lakes near volcanoes have been recorded as dropping to close to 0, which is extremely acidic.  Often sulfuric acid will bubble up through soils into water, causing lakes, ponds, streams, springs, etc. to become highly acidic.


In the movie, one of the more gut-wrenching scenes occurs on a lake of this type.  During their escape, Brosnan, Linda Hamilton, the two kids, and the stubborn grandma must cross a lake near Grandma’s house.  As they paddle desperately, the lake begins to eat their boat and Grandma jumps out to heroically push them to safety, sacrificing herself for the greater good.  This eats her clothes and skin rapidly and she perishes, quite painfully I imagine.


The issue with this is not that it would not happen, but that it would certainly not happen this quickly.  Although sulfuric acid is highly corrosive, dangerous stuff, it will not eat through metal in a matter of seconds or even minutes.  It may take roughly a day for a 5mm metal rod to dissolve in pure sulfuric acid, so the speed at which the acidified lake, which would still likely not be pure acid and therefore less corrosive, corrodes the boat is slightly (cough, cough) exaggerated.


Could people be boiled alive in a hot spring as a precursor to an eruption?


Again, this question encompasses a few things in this movie.  It alludes to the dead animals, trees, shrubs, and of course, the boiled-to-death teenage couple in the hot springs.  This is all supposedly related to CO2 seeping from the ground as an effect of the awakening of the volcano.


Phenomenon such as this has been documented as a precursor to volcanic eruptions.  Often, as a byproduct of gases that are escaping from the magma chamber as the pressure from the rising plume pushes them outward will contaminate the atmosphere above the chamber.  Elevated CO2 levels in the air can suffocate animals, and CO2 saturation in the soil can lead to suffocation of plants.


The one thing here that is quite hokey is the boiling hot spring.  Although some springs and other bodies of water have displayed increased temperatures prior to an eruption, they are not nearly hot enough to boil someone to death.  The movie depicts this phenomenon as happening quite quickly as well, as the spring is nice and inviting when the teens show up.  As they are swimming and enjoying themselves, the spring suddenly heats up to boiling temperatures and cooks them alive.  Bummer dude.


This would not only likely not happen at all, but it would certainly not happen that quickly.


How might one outrun a pyroclastic flow?


In short, you would not.  These monsters can travel at speeds up to 450/mph, So no, just no.

Final Word:


I saw Dante’s Peak around the time it came out in 1997.  I was about 12 years old and it was randomly on television at my grandparents’ house in Cincinnati.  I remember being very intrigued by Dr. Dalton and his crack team of volcano scientists and their tools, lingo, and ultimate heroism.  This movie may be one of those deep-seeded reasons why I ultimately became a geologist (although I study sedimentary rocks and have been known to abhor volcanics).


I remember feeling the frustration that the USGS scientists felt as they tried to decipher the message that this living, breathing, beast of nature was encoding.  I remember being exasperated at the Mayor, her townspeople, and even one of the USGS honchos that were far more concerned about the potential economic harm of evacuating the town rather than the potential harm of the town being wiped out and everyone killed (“Gasp!  But this is our tourist season!”).   Such is the life of a volcanologist: always chasing “The Big One”, being everyone’s hall monitor in the face of resistance and economic concern, and risking your life to measure sulfuric gas emissions…..sigh.  


What I also remember, as both an adult and child, is that I really enjoyed this movie.  The science is generally solid (save for a few nonsensical Hollywoodisms), the acting is good, the special effects around the volcano are well executed and realistic, the plot is believable, and it is overall very entertaining.  As a bonus, the final scene in the movie is actually a shot of the Mt. St. Helen’s Caldera (framed as Dante’s Peak), a foreboding reminder of the destructive power of nature.  The movie itself was filmed in the mountains of Idaho, which are some of my favorite stomping grounds (although they have no relation to the Cascades).  All things considered, even as a scientist it is easy to enjoy and be entertained by this movie, even as you smile wryly during their drive over flowing lava.  Enjoy it Rockheads!

May The Goat be always with you

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