In university, I took a grad course in vulcanology. By the end of the semester, I didn’t learn a damn thing about Spock, but I did learn an awful lot about volcanoes. Combined with the knowledge imparted by the various other courses suffixed by -logy or prefixed by geo- that rounded out my degree in Earth & Planetary Science, I came away with a much greater understanding of our planet and the universe it resides in – as well as a bounty of ammunition to pedantically level at Hollywood and its laughable attempts at “science.”
While it often requires no special education to point out absurdity or plot holes in disaster movies, here are five mistakes and oversights I’ve seen in volcano movies that may not be obvious to everyone.
The usual disclaimer: We are analyzing the science in fiction not to take away from the work as a piece of fiction, but simply For Science! Regardless, “because STORY” isn’t an excuse for bad science; that’s a cop-out to avoid having to rework a plot element.
1. Volcanoes don’t form wherever the hell they want to
In the 1997 movie Volcano, Los Angeles is suddenly attacked by a killer volcano! Fortunately for you Los Angelites, that plot is about as realistic as the alien-invasion Battle for Los Angeles flick. Possibly even less realistic.
Volcanoes form in very predictable places: over so-called “hot spots” like Hawaii and Iceland, and in “volcanic arcs” like Japan or the Cascade Range (which includes Mount St. Helen). Hot spots are fixed regions far below the Earth’s crust that give rise to volcanoes on the surface. While the hot spot remains in a fixed position, the drifting of tectonic plates above a hot spot over time results in one active volcano followed by a chain of extinct volcanoes, like the Hawaiian islands.
Volcanic arcs form near “subduction zones.” The Earth’s crust is divided into a number of tectonic plates that are constantly forming, melting, and interacting. Plates can interact in three ways. The Mid-Atlantic Ridge, for instance, is an area where two plates are spreading apart, allowing magma to flow up from the mantle and form new crust (new plate material). The San Andreas fault is a region where two plates are sliding by each other, causing earthquakes due to the friction of the plates rubbing against each other. The third form of interaction is collision between two plates, which results in one plate being “subducted” under the other and back into the mantle.
When the plate is subducted back down into the mantle, the heat and pressures it experiences squeezes water out of it (yes, rocks contain water!), and that water causes melting in the mantle which gives rise to volcanic activity on the surface in an arc-like pattern, when viewed from above. The arc of the islands of Japan are a terrific visualization of this phenomenon.
Los Angeles is located neither near a hot spot nor a subduction zone. It is near the previously-mentioned San Andreas Fault – earthquakes yes, volcanoes no. Mexico’s Paricutin volcano is an example of a volcano that formed very suddenly (by geologic standards), but that region is a subduction zone. All the script writers had to do was place their fictional volcano in any of the world’s many volcano-forming regions for the concept to be plausible.
SIDEBAR: The volcano island
I live in the Canadian city of Montreal, named after the hill in its center known as Mount Royal (Mont Real). A popular misconception around here is that Mount Royal is either a dormant or extinct volcano. No, it is not. Mount Royal isn’t a volcano, it wasn’t a volcano in the past, and it never will be a volcano. The type of rock is inconsistent with it ever having been a volcano. My dear grandmother, who immigrated here from Italy decades ago, lives in fear of it one day erupting. And I don’t know how to say, “it is simply a plutonic intrusion of igneous rock” in Italian.
2. Different lava comes out of different types of volcanoes
Hollywood action movie writers wouldn’t have a 9mm bullet shoot out of a sniper rifle, so disaster movie writers shouldn’t have the wrong type of lava come out of a volcano.
In Dante’s Peak, the lava that initially erupts out of the volcano is the classic type of lava that Hollywood loves to depict: fast-moving and flowing. It makes for more intense action scenes, just like fast zombies, right?
Unfortunately, that kind of lava flow wouldn’t come out of the type of volcano shown in the movie, which is clearly a stratovolcano like Mount St. Helen’s. Shield volcanoes, like Hawaii’s Kilauea, produce very fluid and “runny” flows. The material that erupts out of a volcano is what determines its shape.
Shield volcanoes – which look like overturned bronze-age shields when viewed in profile – are the result of very fluid lava spreading far and wide. The cone-shaped stratovolcanoes, on the other hand, result from the buildup of lava that is much more viscous – it moves slowly, even downhill, and flows much thicker.
Dante’s Peak later depicted the correct type of lava flow, but that makes just as little sense. Now your sniper rifle is firing 9mm and .50 BMG rounds.
3. Lava is HOT
Lava is hot. Real hot. We’re talking between 1,292 and 2,192 °F (700 and 1,200 °C). Your household oven tops out at 500 °F, and you wouldn’t want to keep your hand in there for any significant amount of time.
There’s a scene in Dante’s Peak in which our intrepid heroes drive a truck over an active lava flow. The top of the flow has cooled enough through contact with the air to form a crust, but you can tell the flow is still active by the FLAMES EVERYWHERE. Lava is so hot that even the heat radiating from it into the air is enough to make nearby vegetation burst into flames. People approaching too close to lava flows will see their skin blister in moments, and depending on the wind direction, burns and singed hair can follow. While flying a helicopter 600-1200 feet above a lava flow, a geologist was able to feel the heat through the windows.
What would have actually happened to that truck driving over the lava? The tires would have instantly melted, the fuel in the gas tank would have rapidly boiled and exploded, most of the car’s chassis would have melted away, the passengers would have caught fire, and the movie would have had an abrupt ending. Or something close to that.
4. Lava is DENSE and VISCOUS
Dante’s Peak at least got one thing right: viscosity. Lava is very viscous – you may say it’s “thick,” like honey.
As a frame of reference, honey is between 2,000 and 10,000 times as viscous as water, chocolate syrup is between 10,000 and 25,000 as viscous, molten chocolate is 45,000 to 130,000, lard is about 100,000 as viscous, and peanut butter is about 250,000 as viscous. Even the smoothest flowing lava can be 100,000 more viscous than water – about on par with tar. So when we see Gollum fall into Mount Doom at the end of the Lord of the Rings trilogy, he probably sinks into the lava too quickly for such a viscous material.
But that’s assuming his bones are made of adamantium. In fact, no human being (or similar living being) could possibly sink in lava. When a drop of oil falls into a glass of water, it doesn’t sink – it floats on the surface, because oil is less dense than water. Similarly, a human body – which consists mostly of water – is much less dense than liquid rock, and would float.
Also, Gollum would have burst into flames.
There’s a scene in Volcano (skip to the 50 second mark in this video) in which someone jumps onto a lava flow and sinks right down into it. At least, that’s what seems to be happening, until you realize that the lava is only a couple of inches deep and that the actual situation the screenwriters were trying to depict is far more ridiculous: the man is melting into the lava. Human beings don’t melt. They burn. Lava isn’t some special substance that melts things – it’s just really, really hot.
5. That’s volcanic ash, not fuzzy snowflakes
While it may look scenic, you don’t want to stay in an area in which volcanic ash is raining down on you heavily. It’s not snow, and it’s not dust. It’s tiny particles of rock that have been shattered through the explosive power of an eruption. In other words, it’s dense material. Depending on the type of ash, we’re talking over ten times the density of sawdust, four times the density of flour, or twice the density of dirt.
The weight of two inches of ash is orders of magnitude higher than the weight of two inches of snow. About 10 inches of dry ash would collapse a roof – five inches or fewer is all it takes if the ash is wet, which can often be the case. In Dante’s Peak, the special effects team used shredded newspaper to simulate falling ash. The result was something that looked a lot more like snow – light and fluffy.
Plus, ash is abrasive – depending on the composition, inhaling ash can be the equivalent of breathing in tiny particles of shattered glass. Breathing difficulty, eye and skin irritation, and nose and throat symptoms are common for those exposed to ash falls, and we’re not even talking about the kind of apocalyptic scenarios depicted in the movies.
For three years, I worked in a geochemical laboratory, and part of my job was operating the heavy machinery in the “Crushing and Grinding room” that ground rock into a fine dust for analysis. This invariably led to some amount of rock particles suspended in the air, and after a few hours, I’d be covered from head-to-toe in a fine layer of dust. I had to wear a mask to avoid inhaling the dust, as do any workers in a field that involves cutting rock, such as the granite industry, because silicosis is a very real health hazard – one that can lead to permanent and irreversible lung damage.
But volcanic ash can be even worse, because depending on the eruption, the particles can be so dense and hot that they’ve been known to cause death by burning or asphyxiation. We call the deadliest of these “pyroclastic flows,” or as the French say, nuée ardente – burning clouds. It was pyroclastic flows that killed 16,000 people and buried the towns of Pompeii and Herculaneum under up to 20-60 feet of ash during the 79 eruption of Vesuvius. Currents of hot gas and ash sped away from the volcano at up to 450 mph at temperatures of up to 1,830 °F – roiling, churning, burning death.
Leave a comment letting us know about the Hollywood science mistakes that drive you crazy! Oh, and the one thing disaster movies always get right? Yes, geologists are all dashingly handsome, adventurous hero-types.
