Bad Geology Movies: Dante’s Peak, 1998

Dante’s Peak

1998

Pierce Brosnan, Linda Hamilton

Premise: What if a seemingly dormant volcano in the Cascades suddenly exploded back into life?

As “Bad Geology Movies” go, Dante’s Peak is not the worst. It has some errors, but at least it gets quite a few things right:

1) The Cascades is a great place to have a volcano suddenly go off, because it is volcanically active and it has had volcanoes (relatively) suddenly explode. Mount Saint Helens, in 1980, only gave a few months of warning before it blew its top. Other volcanoes have been known to go from dormant to exploding in even shorter time frames.

2) The killing of plants and fish by carbon dioxide emitted from vents originating from deep magma bodies is also known to happen. But this does not always mean eruption is imminent.

The movie was not without its errors however.

1) I found it troubling that the volcanologist, played by Brosnan, seemed not in the least bit alarmed by a pH of 3.58 in the mountain lake. That’s a pretty low number, which means it’s pretty acid. With a pH so low, the fish in the lake would surely have been affected in some obvious way (especially since the carbon dioxide had already killed trees). I wouldn’t go in that lake.

2) When the volcano first went off, there was a severe lack of lahars. Lahars are fast-moving slurries of ash, mud, and water that tend to take out towns at the bases of volcanoes. Usually, the water comes from the sudden melting of the snow and ice capping the previously quiet volcano. Dante’s Peak had a significant snowcap, but there were no lahars, at least not right away. There finally were some lahar-like flows toward the end of the movie, but I felt like they needed to be earlier on.

3) Brosnan’s character shouts during an earthquake, “They weren’t tectonic! They were magmatic,” suggesting that somehow, by the way the Earth shook he could tell that the earthquake was not from motion on a fault, but from the movement of magma below the surface. In real life, a person experiencing an earthquake first-hand is not going to be able to make such a distinction.

4) The flows! Ah, the flows! They’ve mixed their flows! An eruption such as this is most likely to only have magma (lava once it erupts) of a single composition. The composition of a magma (how much silica, iron, and magnesium it has, for example) dictates how it flows. One of the earlier eruptions of the volcano has smooth, fast-flowing, ropey magma (known as pahoehoe), indicative of what’s called “Mafic” magma. Later, the characters are stopped by a slow-moving, lumpy flow, similar to what we call A’a’. This type of flow is more expected of “intermediate” to “Felsic” magmas. The truth is that one would not expect mafic magma from a volcano in the Cascades. If I recall, I laughed out loud when I saw that fast flow chasing down the main characters. The slow-moving, lumpy flow is more of what we would expect from a volcano in the Cascades.

5) Whatever the composition, it must be said that one would never, ever be able to drive a truck across an active lava flow. The heat would be so intense that the vehicle and its occupants would begin to burn almost immediately. The main characters should have been incinerated. But it’s Hollywood, so that’s ok.

6) Speaking of characters being killed, there were two more ways in which the entire cast should have died. First, inhaling all that ash that was snowing down would be lethal. It’s nothing more that microscopic shards of glass. Any animal inhaling that would die of massive hemmoraging in the lungs. As it happens, this is how some of the most spectactular fossil localities that we have were formed. Second, when they all stopped to look back and watch the volcano explode, they weren’t far enough away to be safe. The ash and debris would have buried them, if a mudslide hadn’t of taken them out.

But all told, the premise of the movie was realistic – much moreso than others I have watched of late. There is definitely some Hollywoodization taking place, but it has to be there.

I liked the movie and only cringed a few times because of bad science.

If you want a different insight into the film, check out this website.

Bad Geology Movies: Deep Impact, 1998

Deep Impact

1998

Robert Duvall, Téa Leoni, Elijah Wood, Morgan Freeman

Premise: What if a comet was discovered that would strike the Earth in one year’s time? What would we do?

The truth is I really thought this would be ‘bad’ in ways similar to have Armageddon was ‘bad,’ but it wasn’t. Deep Impact is much more a human-interest movie than a science movie. The writers glossed over a lot of the scientific details to get to the story. Since I fancy myself a writer, I appreciate this. In truth, a movie or book or whatever can get itself into trouble by trying to be too realistic or accurate when such accuracy isn’t necessary.

On the whole, I liked the movie (except for that it made me cry a little). Nothing in the science made me groan because they omitted most of the science. I’m all right with that.

One thing I did enjoy, however, is at the beginning, when the journalist played by Téa Leoni discovered the meaning of E.L.E. (Extinction Level Event) on the Internet. She found herself on the UC Berkeley Department of Paleontology website. And you know, I think I’ve been there. More than once.

Yay! A nod to the science of paleontology.

That’s really all I have to say.

Bad Geology Movies: 10.5, 2004

10.5

2004

Kim Delaney, Beau Bridges

 

Premise: What if there were a whole series of mega-deep faults under the western coast of the United States that could trigger a magnitude 10.5 earthquake in Los Angeles?

 

 

This was a television miniseries with two episodes, presumably each of two hours duration. This movie has some of the most absurd instances of pseudoscience that I have ever observed. It was bad. I don’t even know where to begin. So I’ll begin at the beginning.

The show opens with a massive earthquake in Washington state. I admit I wasn’t paying attention to where the seismologists were, but what I do remember is this:

1) Somehow the magnitude of the earthquake – a single earthquake, mind you – increased over time. That doesn’t happen. One earthquake comes from a single rupture/break/motion on a fault. The shaking starts, then it tapers off. Now if other earthquakes were triggered, well, they’d be separate earthquakes and have their own magnitudes.

2) You can’t measure magnitude while the earthquake is happening. This is measured after the fact, using the complete seismographic record. You need to know the timing of all the various seismic waves generated by the earthquake and their magnitudes. You can do that pretty quickly after the quake is over, but not while it’s happening.

3)Speaking of seismic waves, you’d never have “s-waves off the chart!” as exclaimed by one of the movie’s characters in reference to this first quake. S-waves tend to be pretty small compared to the surface waves (which are the ones that do all the damage). Maybe the writers thought that s-waves and surface waves were the same thing… Not.

4)The claim is made by the main character that the earthquake hypocenter (the point in the Earth’s surface where the fault movement is actually taking place) is ‘sub-asthenosphere.’ She later asserts that the earthquake hypocenter must be about 700 kilometers down. Rocks at that depth do not fracture and form cracks or faults. It is solid rock (part of the lower mantle), but temperatures and pressures are so high that the rock will stretch, atom-by-atom, rather than actually fracture and form a fault.

As the movie progressed, there were still references that baffled me.

1) The main character talked about side-to-side motion from the earthquake, later getting excited when she realised it wasn’t side-to-side, bu lateral-skip. Seriously, I have no idea what that is…

2) They made measurements of the magnetic field, for radon gas, and collected soil samples to “prove” these 700-km-down faults. I have no inkling of how that would work. I mean, maybe a magnetic anomaly is something that could happen. Actually, no. I don’t think so. And what about those ruptured pockets of poisonous gasses? Where are those coming from? No idea.

3) There were these wierd thermal activity maps (or something) with which they were identifying the stresses building up prior to a quake. From this, they were predicting earthquakes heading south down the west coast. Again, I have no idea what that was. No such thing exists. And we can’t predict earthquakes.

The funniest part of the movie is when they proposed to fuse the San Andreas Fault using nuclear warheads. Why must all the ‘bad geology movies’ involve nuclear weapons? Anyway, you can’t fuse a fault. You can’t. You can relieve some stress, and maybe mitigate a potential earthquake, but you can’t fuse a fault. Sorry.

The second episode was nearly as funny as the first. (I don’t think it was supposed to be funny, by the way.)

They were drilling their seven (or was it five, or six) perfect holes for the nuclear warheads. The director of FEMA was overseeing each one (why?!). The drilling was slow though. You know why? “Solid layers of rock, all the way down.” What did they expect? Caves? Marshmallows? Of course, the drill they used was also ridiculous, but we’ll let that go.

There’s this river that changes direction after a massive earthquake. I questioned our seismologist’s cognitive abilities after she suggested that a magnetic field could have caused the river to change directions.

The climax of the film is where the San Andreas fault opens up – complete with crazy gas fissures – causing part of southern California to become an island. This follows the misconception that activity along the San Andreas fault will cause part of California to slip into the sea. That’s simply not true. The San Andreas slips such that western California will simply move northward along coast of North America until if finally hits Alaska. It is not going to sink into the sea!

Nor would any fault (even one rooted in the mantle, 700 km down) suddenly open into a vertical-walled chasm over the course of only a few minutes. Though I suppose it does make for good TV. Provided you know NOTHING about geology.

Sigh.

There are other glaring errors and weirdnesses in the movie, but I think I’ll stop there. This movie has its problems. Of all the recent movies (1990’s and newer) I’ve watched and reviewed thus far, this one seems to have the most scientific errors. I think I was actually yelling at my computer as I watched it. It was that bad. Maybe the personal stories in the movie were cute and touching, but I couldn’t get to that, because the science was so awful. That’s my curse.

By the way, there’s a sequel to this: 10.5 Apocalypse. I won’t be seeing that.

Beware of Movies! Earthquakes and Tectonics

The Beware of Movies! series is meant to point out some of the scientific inaccuracies of popular movies, specifically in points related to the geological sciences.

This post will point out the major inaccuracies portrayed in movies about earthquakes, and the mistakes that are made regarding how the important theory of Plate Tectonics works.

 

Let’s start with earthquakes. Earthquakes are shaking of the earth, typically due to motion along a fault. There are other things that can cause earthquakes, but we won’t worry about those here. Not yet, anyway.

FAULTS

So, what’s a fault?

Most of us have a general sense of what a fault is. It’s a big crack in the Earth’s crust, across which motion (or slip) can occur. Americans usually think of the San Andreas Fault, which cuts California from the northwest to the southeast.

There are tons of misconceptions about faults, some of which are carried into the movies and TV that we watch. Let’s first talk about how faults work, and then address these misconceptions.

TYPES OF FAULTS

Faults are divided into to main types: Strike-slip and dip-slip. Strike slip faults are those where the rocks on each side of the fault slide past each other in a horizontal fashion, to the right or to the left. Dip-slip faults occur when one side of the fault moves up or down relative to the other.

The San Andreas Fault is a strike-slip fault. The rock on the west side of the fault is moving northward with respect to the rock on the east side. If you stood on the Sierra Nevada mountains and looked to the West, across the fault, it would look like the west side was moving to the right. Hence, the San Andreas fault is a right-lateral strike-slip fault.

A right-lateral strike slip fault. The dark band was once continuous across the fault. The cat is wondering how is food bowl moved

A right-lateral strike slip fault, similar to the San Andreas Fault. This is looking down on the fault from above. The dark band was once continuous across the fault. The cat is wondering how is food bowl moved

Beware of Movies: In the TV movie “10.5” (and in other movies like the original “Superman”), it was portrayed as if activation of the San Andreas fault would cause California to sink into the ocean. In fact, lots of people still seem to think this. The truth is that more likely, western California would slide up the western edge of North America and collide with Alaska. But don’t worry. That would take millions of years!

A left-lateral strike slip fault. This is looking down on the fault from above. The dark band was once continuous across the fault. The cat is wondering how is food bowl moved

A left-lateral strike slip fault. This is looking down on the fault from above. The dark band was once continuous across the fault. The cat is wondering how is food bowl moved

Many other faults in western North America are dip-slip faults. The fault surface or plane on dip-slip faults tends to be tilted, rather than vertical as in a strike-slip fault. If one were to open up such a fault and try to climb up it, on one side, a person could walk up and on the other a person would need ropes to hang off it. For this reason we call one side of a dip-slip fault the ‘footwall’ and the other side the ‘hanging wall.’

For a dip-slip fault, the motion of the hanging wall relative to the footwall is how we know what caused the fault to form. In faults where the hanging wall moved up with respect to the footwall, we know that compression caused the faulting. This is called a ‘reverse’ fault. If the hanging wall moves down with respect to the footwall, the faulting was caused by stretching, and the fault is called a ‘normal’ fault.

A reverse fault. The cat is standing on the hanging wall. The dark band was once continuous across the fault. The hanging wall has moved up relative to the footwall.

A reverse fault. The cat is standing on the hanging wall. The dark band was once continuous across the fault. The hanging wall has moved up relative to the footwall.

The Wasatch Fault, that runs through Salt Lake City, for example, is dip-slip. It is an example of a normal fault that formed as the continent of North America was stretched out on the west side. All of the mountains of the Basin and Range in the West are bounded by normal faults.

A normalfault. The cat is standing on the footwall. The dark band was once continuous across the fault. The hanging wall has moved down relative to the footwall.

A normal fault. The cat is standing on the footwall. The dark band was once continuous across the fault. The hanging wall has moved down relative to the footwall.

Reverse faults are common in big mountain belts like the Rocky Mountains and the Appalachians. These mountains formed by tremendous forces of compression. There is a special category of reverse faults called ‘thrust’ faults.  Thrust faults are very low angle (close to horizontal) and can slip for hundreds of kilometers. Thrust faults can stack on top of each other (called duplexing) and take up tremendous amounts of shortening of the Earth’s crust.

A thrust fault, a special case of a reverse fault. The cat is standing on the hanging wall. The dark band was once continuous across the fault. The hanging wall has moved up relative to the footwall.

A thrust fault, a special case of a reverse fault. The cat is standing on the hanging wall. The dark band was once continuous across the fault. The hanging wall has moved up relative to the footwall.

These terms for faults are general. It is important to be aware that most faults don’t fall exactly into one of these categories. For example, there is a little bit of compression that occurs across the San Andreas Fault. The Wasatch Fault has a bit of horizontal motion. Faults are categorized by the type of faulting (strike-slip versus dip-slip) that dominates the motion. If a fault’s motion is between strike-slip and dip-slip (it has components of both kinds of slip), a fault might be called oblique-slip. One such fault might be described as “normal right-slip.”

EPICENTER/HYPOCENTER

When there is an earthquake along a fault, the whole fault doesn’t move at once. Parts of it move, while other parts remain stationary. A fault will remain stationary for a long time as stress builds up across it, then SNAP! It goes.

Earthquakes have epicenters, which most people understand to be where the quake originated. More specifically, the epicenter is the spot on the surface of the land directly above the part of the fault that actually moved. There’s a similar term, hypocenter, which refers to the actual spot, deep under the surface, where the fault moved.

To find the epicenter and hypocenter, a geoscientist looks at the seismic waves from the earthquake as recorded by at least three independent seismic stations. There are several types of waves generated by earthquakes, most importantly p- and s-waves. p-waves are “primary” waves, and arrive at seismic stations first. These are compressional waves. s-waves (“secondary waves”) arrive next. s-waves are shear waves, so they won’t pass through liquids. The separation in time between the s- and the p-waves tells the geoscientist how far away the earthquake happened, but not what direction. With several seismic stations, the actual point (the epicenter) of the earthquake can be found.

Beware of movies: The movie “10.5” had all sorts of gems about epicenters, hypocenters and seismic waves. One quote was “the s-waves are off the chart!” which is interesting because it’s not the p- or the s-waves that are the big sweeping squiggles on a seismogram. The big squiggles are from the surface waves, which come much later. The characters also became excited as they looked at seismograms shouting about side-by-side motion. Honestly, I don’t even know what that is. The characters were delighted that the hypocenter was deeper than they could measure (“sub-asthenosphere” even), which is bizarre. Read on about that.

EARTHQUAKE INTENSITY

Intensity of earthquakes is usually measured on the Richter scale, where greater numbers mean a bigger quake. The Richter scale is logarithmic, meaning that a magnitude 5 quake is 10 times as powerful as a magnitude 4 quake. It is measured in reference to how large the surface waves generated by the quake actually are. The first surface waves are usually the biggest, and then they taper off. The fault moves one time – suddenly – then stops. Aftershocks (renewed motion) might occur, but each of those come with their own seismic signature with p-waves, s-waves, and intensity.

Beware of movies: Here’s the thing: Magnitude of a quake is calculated after the quake is over. In 10.5, they’re measuring (somehow) the intensity of a quake as it is happening. What’s more, the intensity of the quake (in the movie) increases over time. That does not happen with real earthquakes!

WHY ARE THERE FAULTS AT ALL?

Obviously, something has to be driving all this compression and stretching and shearing that causes faults to exist at all. The theory of Plate Tectonics provides the best explanation for the existence of faults and the forces that drive their motion.

As mentioned in a prior Beware of Movies! post, the Earth’s surface (lithosphere – down to about 100 km depth) is broken into several plates, which move around. These plates can be divided into two categories depending upon their thickness and composition. Oceanic plates are under the oceans. They are much thinner but are made of very dense material. Continental plates are the continents, and are thicker but not all that dense (as rocks go). Some plates, like the North American plate, have parts that are continental (all of North America) and parts that are oceanic (the North American plate extends halfway across the Atlantic Ocean).

Major tectonic plates of the world.

TYPES OF BOUNDARIES BETWEEN PLATES

There aren’t gaps between the plates, so something has to happen so that the plates can move. There are three general types of plate boundaries: convergent, divergent, and transform. Convergent boundaries exist where two plates are coming toward each other. Divergent boundaries occur where plates are moving apart. When plates slide past each other, we have transform boundaries.

Three types of plate boundaries.

Convergent boundaries involve compression, so it’s no surprise that faults associated with such boundaries are usually reverse faults. The nature of the boundary itself is dependent upon whether the convergence is between two continental plates, or if oceanic plates are involved. If two continental plates are converging, there will be a collision, just like when India hit Asia millions of years ago resulting in the Himalayas. The Appalachian Mountains of North America are remnants of an ancient collision between Africa and North America (which have since moved apart).

An oceanic plate can sink under another plate, resulting in subduction, where one plate overrides another. A subduction zone is like a colossal reverse fault, though we don’t generally call it as such. Subduction also results in mountain ranges, like the Rocky Mountains and the Andes. Subduction is also associated with volcanoes. The volcanoes of the Cascades and of the Andes are related to subduction.

When plates move apart, stretching and thinning of the plates occurs, along with lots of normal faults. The lithosphere gets so thin that magma comes up from the mantle (below the lithosphere) causing a line of volcanoes. When such stretching begins, especially in the middle of a continent, it is called ‘rifting.’ The East African Rift system is a prime example of this.  Lake Victoria sits in the depression caused by the rifting.

At some point the rift becomes so deep that it is filled with ocean water. New oceanic crust is formed by the volcanic eruptions. This is happening in the Red Sea today. As this continues, a whole new ocean forms. The entirety of the Atlantic Ocean was once just a little rift between North and South America and Europe and Africa.

When plates slide past each other, we get transform faults. These are strike-slip faults. Sometimes there’s a bit of volcanism associated with these but usually the big activity there is earthquakes. The San Andreas Fault is a transform boundary between the Pacific plate and the North American plate.

Beware of Movies: The movie “Volcano” is based on the premise that the plate boundary between the Pacific Plate and the North American plate could spawn a new volcano, similar to those in the Cascades. The problem is that there is no subduction along the San Andreas Fault. There is subduction below the Cascades, but it’s not the Pacific Plate that’s being subducted. It’s the small Juan de Fuca Plate. The Juan de Fuca plate is a remnant of a once much larger plate (the Farallon) that has been completely subducted under North America.

WHERE DO FAULTS OCCUR?

Plate tectonics explains that most faults occur due to motions of the lithospheric plates, resulting in a limitation of where faults might be seen on the Earth’s surface. Faults also are limited to the lithosphere, or the upper 100 km or so of the Earth. The lithosphere – the crust especially – tends to deform in a brittle fashion. That is to say, if you put pressure on the rock, it will likely crack and snap. Below the lithosphere, heat and pressure are so high that rock (though it is still solid rock) deforms in a ductile or plastic fashion. It bends slowly or flows, due to individual motions of atoms. Big cracks and fissures do not exist below the lithosphere.

Beware of movies: In the made-for-TV movie “10.5,” the geologist claims that the massive earthquakes are being caused by faults existing 700 km down. Not only is that below the lithosphere, it’s in the lower mantle! Faulting cannot exist at such a depth.

The take-home message here is that earthquakes do not occur willy-nilly all over the surface of the Earth. They are most often associated with plate tectonic boundaries or mountains. There are a few that pop up in unexpected places. Some are even devastating, like the New Madrid earthquake that hit the mid-western United States in 1812. In that case, the earthquake resulted from the re-activation of an extremely ancient fault system that is no longer active, but had accumulated some stress over millions of years. I hasten to mention that the New Madrid fault is still in the crust!

Beware of movies: We don’t know where every fault is. We can’t predict earthquakes. Don’t believe it when characters in movies (like “Earthquake” or “10.5”) claim to be able to do so. It can’t be done. Not yet, anyway.

Geology Movies: John Carter, 2012

John Carter isn’t about geology at all, so it’s really not a “Bad Geology Movie.” However, it’s worth inclusion here because it was filmed in a place that has some really darn awesome geology.

Those aren’t (all) matte paintings folks. That stuff is real! Features might have been added, but the settings are real.

Shiprock

Shiprock. Learn more about this here.

This is the area where I studied geology, all those years ago. Watching John Carter took me home. If you want to see some spectacular geology while watching a movie, you should check out this movie!

Beware of Movies! The Interior of the Earth

The Beware of Movies! series is meant to point out some of the scientific inaccuracies of popular movies, specifically in points related to the geological sciences.

This blog post will point out the major inaccuracies portrayed in movies about the structure and composition of the Earth.

One might think that we have no way to know what the interior of the Earth is like. The Earth is over 6000 kilometers in diameter, and we’re doing good to drill a few kilometers into the crust.

Here’s the reality of the Earth’s structure. At first pass, the Earth is composed of the crust, the mantle, and the core. The mantle and the core are each divided into two parts, the upper and lower mantle, and the inner and outer core.

Structure of the Earth

The crust is the part that we live on. It is very, very thin compared to the rest of the Earth, going down only to about 7 to 70 km (depending on where you are). The base of the crust is marked by the Moho (which is short for the Mohorovičić discontinuity). Below that is the upper mantle down to a depth of about 660 km, followed by the lower mantle down to about 2900 km. It is a common misconception that the mantle, being very hot and under pressure, is molten. This is absolutely untrue. The mantle is solid rock, with one tiny exception in the upper mantle that we’ll get to in a moment.

Below the mantle is the core. The outer core, from 2900 to 5155 km in depth, is the only part of the interior of the Earth that is fully molten. It is composed of molten iron and nickel. It is here where the Earth’s magnetic field is generated. This is one of the few things that were correctly attributed in the movie “The Core.” From 5155 km to the true center of the Earth is the solid inner core, which is composed mostly of iron and nickel.

This simplistic, three-part division (crust, mantle, core) is the extent of the description of the interior of the Earth provided by the movie, “The Core.” Equally, “Journey to the Center of the Earth” (2008) is no better. Both are over-simplifications.

 

Before we move forward, it is probably worthwhile to explore how we can possibly know this much about the interior of our planet. As I already pointed out, we haven’t actually drilled completely through the crust. How can we possibly know the structure or the composition of the interior of the Earth.

The movie “The Core” actually begins to show us how this is done. Solid rock can transmit seismic waves. Every time there is an earthquake somewhere on Earth, it sets off waves that pass completely through the Earth and can be recorded at seismic stations throughout the globe. Some waves pass through the Earth, others can only move along the surface. Seismic stations record both types and seismologists can determine when and where the earthquakes happened based upon when the waves are recorded.

The way that waves pass through the Earth are affected by the types of rock. Some rocks speed up the waves, others slow them down. Waves bounce around inside the earth, too. So a seismic wave might bounce off of the core-mantle boundary. These properties, combined with multiple seismic stations, make it possible for us to know the composition of the Earth and the approximate position of any important boundaries within the Earth.

Furthermore, one type of seismic wave, shear waves, won’t pass through liquids. So if a seismograph recording an earthquake shows no shear waves, we know that the seismic waves went through a liquid. This is how we know that the mantle is solid rock and that the outer core is molten.

Beware of movies: In “The Core,” the terranauts find huge open cavities in the mantle. If such open spaces existed, they would have been evident from seismic studies. No seismic wave could pass through an empty space like that, and we would know about them. Similarly, in “Journey to the Center of the Earth” (2008), the main character discusses the existence of tubes that bypass the mantle and go straight to the core, which in the movie is hollow. Again, seismic waves would have shown such tubes and caverns.

Since earthquakes occur all around the Earth all the time, one needs only to have a global set of seismic monitoring stations, and we can learn all about the Earth’s structure. Such a global network exists. Because of that, we know that the Earth is actually far more complex than just crust, mantle, and core.

 

Many people are aware of the important concept in geology called “Plate Tectonics.” At a first pass, Plate Tectonics explains why it seems like South America and Africa would fit so well together, like puzzle pieces. That’s because they did once fit together and have since moved apart. The moving units on the Earth’s surface are called ‘plates.’ There’s a South American plate and an African plate. They were once together and have since moved apart.

Individual plates are not just pieces of crust moving around on top of the mantle (a common misconception). The plates are pieces of the “lithosphere,” which includes the crust plus the uppermost part of the mantle down to about 100 km. Crust plus the uppermost mantle (called the lithospheric mantle) equals the lithosphere. The crust and lithospheric mantle move as one big piece called a plate.

The structure of the Earth, including the lithosphere.

Below the lithosphere, is the asthenosphere, which goes down to about 400 km in depth – basically much of the rest of the upper mantle. It’s in the asthenosphere that flow occurs.

But wait! The mantle is solid rock! How can it flow?

Two things happen: 1) Just like wax is a solid that can flow, so can the mantle. Individual atoms within the minerals of the mantle can move causing very, very slow flow. 2) Because of temperature and pressure gradients, between 100 and 200 km in depth there is the tiniest bit of melting. The whole rock doesn’t melt, just a few of the minerals. This slows down shear waves, but doesn’t stop them completely, which is how we know this slight melting exists. We call it the low velocity zone, because it slows down the shear waves.

 

The various layers of the Earth have fairly specific compositions. The core is mostly nickel and iron, as previously mentioned. The rest of the Earth’s composition can be explained using Bowen’s reaction series. Read more about it here.

Bowen’s Reaction Series

The basic rocks of the universe are ultramafic rocks, so we would expect that the bulk of the Earth is composed of ultramafic rocks, which are primarily the mineral olivine. Ultramafic rocks are characterized by having high iron and magnesium and low silica.

The crust of the Earth has some mafic rocks and minerals, but most are intermediate to felsic in composition, meaning that there’s high silica, potassium, aluminum, and sodium. These compositions are attained when the mafic rocks of the mantle are melted and erupted, then cycled through the rock cycle multiple times. Every time a rock is re-melted, the most mafic parts of it tend to be last to melt, and might not erupt, resulting in rocks that become more and more felsic over geologic time.

Beware of movies: In “The Core,” the terranauts discover huge amethyst crystals in the upper mantle. Amethyst is a type of quartz, which is a felsic mineral. The mantle is ultramafic. What this means is that quartz would not be stable, it could not exist, in the mantle. This is a big mistake.

Beware of movies: Both “The Core” and “Journey to the Center of the Earth” make the mistake of thinking that diamonds would be abundant in the mantle. The reality is that there are diamonds in the upper mantle, where conditions of temperature and pressure are suitable to form diamonds. And, “Journey to the Center of the Earth” never really specifies where they are in the mantle – probably fairly high, so maybe that’s ok (although there’s an additional problem with muscovite in that movie). In “The Core,” however, they discover huge diamonds presumably in the lower mantle, at least fairly close to the core-mantle boundary. Conditions aren’t suitable for diamonds low in the mantle, lack of carbon notwithstanding. The giant diamonds are bogus.

 

This is the general understanding of the interior of the Earth, and how we know what we know. On this topic, movies are typically either pretty-darn-good or completely wrong. As always, extreme caution needs to be used when trying to apply the science of movies to real life.

*****Added January 15, 2013*****

I’ve discovered that I left some things out of this post. Please visit this post to learn more about what meteorites and magnetism have to do with our understanding of the Earth’s interior.

Bad Geology Movies: The Core, 2003

The Core

2003

Aaron Eckhart, Hilary Swank

Premise: What if the Earth’s liquid outer core stopped spinning, resulting in total catastrophe? Can it be set spinning again?

One thing this movie got right: the Earth’s magnetic field is generated in the liquid outer core. The rest, well—

I enjoyed the opening scene with the main character giving a geology lecture about using seismic waves to understand the interior of the Earth. I’ve given that very lecture. I’m just glad my students aren’t so lethargic. It’s pretty amazing actually, since my classroom is considerably darker. I do have one student who’s often working on his nails, but that’s ok. He plays classical guitar.

Moving on to the geological problems with this movie, and there are many…

1) The whole movie oversimplifies the structure of the Earth, dividing it only into crust, mantle, and inner and outer core. It’s substantially more complex than that. The mantle is divided into two parts (upper and lower), and the movie fails to distinguish between the lithosphere (crust and uppermost mantle) and asthenosphere (part of upper mantle). That’s fine though, I guess. If they keep it simple, they can’t be wrong.

The structure of the Earth

2) As our intrepid terranauts are drilling toward the core and about to pass from the crust to the mantle, one of the ground crew comments that passing through the crust is different than the mantle as “the crust is just rock.” Last I checked, the whole planet was ‘just rock,’ with the only possible exception of the liquid outer core.

3) Our explorers find great empty spaces in the mantle, filled with amethyst crystals. Two problems here: a) Any empty spaces would have been most likely recognized by the behavior of seismic waves through the mantle. Shear waves won’t pass through liquids and NO waves would pass through an empty void. There are no empty spaces in the mantle. B) These (impossible) empty cavities are filled with huge amethyst crystals in the movie. Amethyst is a variety of quartz. If one takes a moment to look at Bowen’s reaction series, one would find that quartz is common in felsic rocks, like continental crust. The mantle is ultramafic rock. There isn’t enough silica to make quartz. Quartz would not be stable there. Quartz does not exist in the mantle. But, to give credit where credit is due, at least they got the shape of the crystals right!

4) Somewhere low in the lower mantle, our terracraft bumps into (literally) a bunch of enormous diamonds. I can see the movie-maker’s thinking here: Diamonds form under intense pressure, thus there must be huge diamonds near the Earth’s core. One problem though. Diamonds are composed entirely of carbon. There just isn’t enough carbon in the mantle to make diamonds. At all. Certainly not the gigantic ones portrayed in the movie. That point aside, I have no idea on what basis the identification as ‘diamond’ is made. They certainly don’t have the proper octahedral shape of diamonds. I guess because they show up as black and are thus impenetrable, then they can only be diamonds.

5) They set off the nukes and achieve “full rotation” of the liquid outer core (whatever that means). As I understand the flow of the outer core, it’s not quite as simple as shown in the movie. We call the flow of the liquid outer core, and how it generates the Earth’s magnetic field, the magnetic geodynamo. This link will take you to several other pages that will explain better how this works.

6) The final facepalm of the movie was when the terracraft finds itself launched out from the core and back to the sea floor through a “space between tectonic plates near Hawaii.” Hawaii is smack-dab in the middle of the Pacific Plate. There are no plate boundaries there. Now it is a hot spot, and the crust might be thin, affording an easy exit for our terranauts, but there is no plate boundary.

So these are the major geologic problems with the movie “The Core,” or at least the ones I spotted in the feverish state I was in while watching the film. Read my review of “Journey to the Center of the Earth,” for a completely different yet equally incorrect perspective on what Earth’s interior might be like.

Be careful should you start to think that what’s portrayed in movies has any basis in reality (at least as is understood by science).

Bad Geology Movies: Armageddon, 1998

Armageddon

1998

Bruce Willis, Ben Afflek, Liv Tyler

Premise: What if a Texas-sized asteroid were careening toward Earth and we only had 18 days to stop it?

The idea is an interesting one. We know that there was an asteroid impact on Earth at the same time the dinosaurs went extinct and there is a lot of evidence to suggest that the impact itself was a huge factor causing the extinction. So, what if it were about to happen again, only now we were able to detect the oncoming asteroid and could (potentially) do something about it?

In the opening sequence, the narrator describes the dinosaur-killing asteroid as six-miles wide. That may be right. It seems reasonable, anyway. The narrator goes on to describe a global dust cloud which lasted for 1000 years, through which the sun could not penetrate. For the sake of the movie, that’s as good as anything. But do be aware that there are plenty of competing hypotheses about what happened after the impact. Some involve incinerating the Earth, not coving it with dust. Or triggering volcanoes. Or all of the above. But, that there was an impact is no longer debated.

Since this is about bad geology movies, I won’t go into the details of problems with the rest of the movie aside from the geology. The movie was fairly fun… until they were on the asteroid. Then I started having problems.

1) Our characters miss their landing site by 26 miles. They wind up in a region of “compressed iron ferrite.” They also describe it as a compressed iron plate. Iron ferrite is not any mineral or rock that I’ve heard of. “Ferrite” as a word on its own, is another word that means ‘iron.’ So iron ferrite is an iron-bearing iron rock (or mineral, they never clarify). So it’s redundant. You see the phrase “Iron Ferrite” on google, but I suspect people put the two together because most folks don’t realize that the ‘ferrite’ part already says ‘iron.’

2) All over the place (on the asteroid) are huge crystals jutting all around. It’s reminiscent of Superman’s home planet of Krypton, or perhaps his Fortress of Solitude up in the Arctic. Such crystals aren’t going to form in the vacuum of space, especially not in an area composed entirely of iron ferrite. They looked like gypsum crystals, which wouldn’t make much sense on an asteroid.

3) The topography of the asteroid was bizarre. One would expect craters, with steep slopes and whatnot, but not a “Grand Canyon.” A canyon like that is an erosional feature, that you wouldn’t expect on an asteroid. But maybe it was a great big crack in the asteroid. Why then did they not drill there, where the rock was already fractured and weak?

4) One more thing bothered me, but maybe it’s not so bad. This asteroid seemed to have an atmosphere. There were the random fireballs which made no sense to me. And then the wind blew, slightly, at the end when Bruce Willis’ character picks up some of the dust and let it fall from his hand.

There was just a lot wrong with the asteroid, which spoiled the movie for me, mostly. The movie was enjoyable otherwise, with some fun and charming characters.

Beware of Movies! Foundations of Geology – Minerals and Rocks

Beware of Movies! will be a series of blog posts discussing important concepts in geology while making reference to scientific errors in movies and TV regarding geological concepts. These posts go in concert with a lecture series I’m preparing with the same idea. It seemed fun.

This is the first post in the Beware of Movies! series.

A common misconception about geology is that it is a science ONLY about minerals and rocks. Well, and oil. But that’s it. Geology is a tiny bit more complex than that. However, it does include rocks (and minerals) as an important fundamental basis. A person can’t say much in any field of the earth sciences without first knowing quite a bit about minerals.

MINERAL:

1) Naturally occurring

2) Inorganic

3) Solid

4) Specific crystalline structure

5) Specific chemical composition

Any compound that fits the above definition is a mineral. Ice (frozen water) is a mineral because it satisfies these criteria.  Bismuth hopper crystals do not satisfy these criteria because they’re synthetics, so, while quite lovely, they do not constitute a mineral.

CHEMISTRY:

When I start to talk about chemistry, my Introductory Geology students always groan. But I’m always able to assure them that what matters here is pretty basic and that it’ll be over soon. Chemistry matters because minerals have a specific chemical composition. This means that the individual atoms that go into a mineral are specified. The atoms are specific elements, like carbon and oxygen, and certain numbers of each of them combine (bond) to form the minerals. I will spare you the details of how the atoms bond. What’s important is that atoms have size. They’re like little spheres of differing sizes depending on the elements. When you try to stack the elements together, they stack in very specific ways. That is what causes the crystalline structure of minerals.

The stacking of the elements forming a mineral also results in all the recognizable properties of minerals that we use to identify them, including:

Color – what color is it?

Luster – how would we describe the shininess of the mineral? Metallic, earthy, glassy.

Specific gravity – how dense is it?

Crystal form – what shape are the crystals?

Cleavage and fracture – how do the crystals break? Do they break along specific planes or along random surfaces?

Hardness – is the mineral soft, like talcum powder, or hard like diamonds?

MINERAL GROUPS:

Minerals are grouped by their basic chemistry:

Oxides – have oxygen (O) like Fe2O3, hematite (rust).

Sulfides – have sulfur (S) like PbS, galena.

Sulfates – have sulfate (SO4) like CaSO4 H2O, gypsum.

Carbonates – have carbonate (CO3) like CaCO3, calcite (chalk).

Native elements – gold, silver, carbon like diamonds!

Silicates – have silica (The silica tetrahedron – SiO4) like SiO2, quartz

Beware of movies: In Armageddon (1998), our heroes are forced to drill into an asteroid to implant a nuclear device. Where they wind up setting down, so claim the characters, is composed of “iron ferrite.” That’s not any mineral I’ve heard of. It’s a redundant name, actually, because the ‘ferrite’ part, like ‘ferric’ or ‘ferrous,’ refers to iron. So iron ferrite is an iron-bearing iron rock.

SILICATES:

This is the most important group of minerals on Earth, in that they constitute most of the Earth. Therefore, oxygen and silicon are the most abundant elements on Earth. Life is carbon-based, but we’re just a think veneer on a very, very large sphere. But if silicon is so common, why are there not silicon-based life forms?

Silicate minerals are categorized by how the silica tetrahedra relate to each other in the mineral. They can be isolated, or bonded to one another by sharing the one or all of the oxygens on the tips of the tetrahedra, to form chains, sheets, or complex networks. While this sounds like there’d be lots of silicate minerals, it turns out that there are relatively few that a person needs to know to be able to identify most minerals in ordinary rocks. We’ll get to that in a moment.

ROCK:

A rock is an amalgamation of individual mineral grains. Often there are several minerals in a rock, like granite that contains quartz, biotite, and two types of feldspars. But a rock can be composed of grains of all one mineral. The best example of this is a nice clean sandstone which can be made of only quartz grains.

Beware of movies: In Journey to the Center of the Earth (2008), Muscovite is called a “thin rock formation.” Muscovite is a mineral, not a rock. It does make nice thin sheets (because of its cleavage), but it’s not a rock.

BOWEN’S REACTION SERIES:

Bowen’s reaction series describes the stability of silicate minerals under different temperature regimes. Minerals at the top of the reaction series, form under conditions of extreme heat, but are not stable at the lower temperatures at the Earth’s surface. Minerals at the bottom of the series are more stable at low temperatures (like those on the Earth’s surface).

Understanding Bowen’s reaction series will help anyone identify minerals in a rock. See, the minerals that go together in a rock aren’t just randomly selected. Certain minerals occur together. Some minerals are never found together in a rock. The minerals that can occur together are those that are stable at the same temperature ranges. So Olivine and Quartz will never occur in the same rock, for example.

The minerals that are stable at high temperature are the mafic minerals, which are high in magnesium, iron,and calcium, and low in silica. The minerals that are stable at low temperatures (and are common on the Earth’s surface) are called felsic minerals, and are high in silica and hight in sodium, potassium, and aluminum. This doesn’t matter now, but will matter later when we think about volcanoes.

Beware of Movies: The movie “The Core” seemed to struggle a bit with Bowen’s reaction series. The mantle of the Earth (the layer below the crust, where we’re living), is composed of ultramafic rocks. This means, high iron, high magnesium, and low silica. However, in the movie, the intrepid ‘terranauts’ find themselves in a large empty cavity in the upper mantle that is full of amethyst (quartz) crystals. Quartz is felsic. It would never be stable in the mantle. This is a massive mistake.

ROCK GROUPS:

All rocks on Earth can be divided into three groups (and some might fit into more than one).

Igneous rocks: Those rocks that formed from the cooling of molten rock (magma). In these the crystals that make up the rock form according to Bowen’s reaction series (as well as the composition of the magma itself).

Sedimentary rocks: Rocks that formed from the deposition of bits and pieces of other rocks that have been broken down and (probably) transported elsewhere. Alternatively, sedimentary rocks can form from the precipitation of crystals directly out of water, rather like hard water deposits.

Metamorphic rocks: If pre-exisiting rocks of any kind are subjected to great heat and/or pressure, the minerals present, and their relationships to one another may change. This results in metamorphic rocks.

Beware of movies: Bowen’s reaction series helps explain what silicate minerals might go together. There are similar limitations on what other minerals might occur together by what rock type they will be found in. In Journey to the Center of the Earth (2008), they find rubies, emeralds, and diamonds together in a lava tube. None of these would occur together. Emeralds are usually found in felsic igneous rocks. Rubies are found in metamorphic rocks, and diamonds form deep in the mantle, far away from either of the places where emeralds or rubies might form.

ROCK CYCLE:

Any of the three types of rock (igneous, metamorphic, or sedimentary) can be changed into any other type of rock in what is called the rock cycle. Existing rocks can be melted and cool again to make new igneous rocks. Existing rocks can be broken down, transported, and redeposited into sedimentary rocks. And any existing rock can be exposed to high heat and pressure to form a metamorphic rock. The end result is that there are very few tremendously old rocks on Earth, because most have been recycled.

These are some of the basic concepts necessary to understand further topics in geology. Without this basis, it would be impossible to begin to interpret the Earth’s history from its rock record.

Bad Geology Movies: Volcano, 1997

The first in a series of posts about what’s wrong in movies with geology-related themes.

Volcano

1997

Tommy Lee Jones and Anne Heche

 

Premise: What if a volcano appeared and started erupting under a populated area like Los Angeles?

 

I guess one could suppose that because there’s a plate tectonic boundary (the San Andreas fault) there along the margin of North America that a volcano might arise. There’s volcanoes all around the margins of the Pacific Ocean – along plate boundaries – which are given the apt name of “Ring of Fire.” The Cascade Mountain Range, including Mount Rainier and Mount Saint Helens are such volcanoes.

One problem: These volcanoes occur along subduction zones, where basically the ocean floor is being drawn under the larger continents. The Pacific Plate (under the Pacific ocean) is being subducted under Alaska (the Aleutian Islands) and under Japan and in lots of other places. Under the Cascades, the Juan de Fuca Plate is being subducted. The Nazca Plate is being subducted under South America, resulting in all the volcanoes associated with the Andes.

Alas, subduction is NOT occurring in California. There, the Pacific Plate is moving northward with respect to the continent of North America. The San Andreas fault is what is called a “transform” fault, where the rocks slide past each other, not where some rocks override others (like in a subduction zone). Because of this, we can’t expect huge volcanoes like we see in the Cascades. Usually, if there are volcanoes along transform faults, they’re pretty small. They’re not completely impossible, so the possibility exists.

Of course, the explanation provided by the geologist in the movie, Dr. Amy Barnes (played by Anne Heche) is not like this at all. And in the end, they get a new mountain out of the deal, which is highly unlikely. We’ll just ignore that…

There are lots of things that bug me about this movie, from the stance of a geologist – the likelihood of a volcano in LA aside.

1) I really don’t think the K-rails are going to do much to block flowing lava. And dousing it with water? Well, I guess they do these sorts of things elsewhere with some success. But the movie makes it out like they stopped the flow of lava completely. I suspect that in the real world, the best outcome in such a situation is a diversion of the flow. That stuff’s hot! And there’s a lot of it! Let’s send it somewhere else and we’ll be OK – which is what they did in the end. (And how come no one except for the geologists had any idea what ‘lava’ was?)

2) A greater problem is that they should have all died of massive bleeding in the lungs before they even had a chance to try to block the flow of lava. Ash is basically fine shards of glass. No one was wearing masks, so they were basically inhaling glass. For hours. Not one cough. No sneezing. No gasping. Right.

3) The news report at the end made me facepalm. ‘The volcano is shutting down,’ the reporter said. ‘The lava is subsiding.’ Volcanoes don’t just ‘shut down,’ and lava doesn’t ‘subside.’ Once the lava’s on the ground, it’s solid. There is no subsiding. Maybe they were referring to magma deep within the Earth. Anyway, the idea that a volcano can just turn on and off like that is extremely sketchy, though mightily convenient for a movie.

4) Dr. Barnes mentions that the bible verse Matthew 7:26, “And every one that heareth these sayings of mine, and doeth them not, shall be likened unto a foolish man, which built his house upon the sand,” is very popular among geologists. Strangely, I’ve never heard that one before. Just saying.

I won’t go into the other gripes and hilarious things that happen in the movie, as they are not related to geology. I will say that the movie was clearly pre-9-11, and I loved the giant cell phones. I did get into the story sufficiently that I was engaged with the main characters and glad that everyone came out OK. It’s not the worst ‘bad geology movie’ I’ve ever seen.