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ES 10
Extra Credit Problem - Dante's Peak
Answer Sheet

This answer sheet is designed to give a very brief set of answers to the questions in the Dante's Peak extra credit problem. There are a number of very good, detailed web sites which have answers to common questions about Dante's Peak, and I will not bother trying to reproduce what others have already done better than I ever could.

Instead, I will briefly give some answers, and then pointers as to where to go if you want to know more.

Feel free to ask me questions or send me comments via e-mail. My e-mail address is

The maximum number of points possible on this assignment was 50.

Table 1:   Extra Credit Grading Scale


Part A: Important social and political factors

This question could easily be the subject of a very long research paper, but for this assignment, brief was great. There are lots of social, economic, and political factors which need to be taken into account in a potential eruption situation.

First off, nobody wants to see people killed if it can be avoided. So people's safety has to take absolute priority. That said, how do you balance protecting them physically and ruining them economically? If you predict an eruption, and you alert people, and the towns are evacuated, and the volcano erupts, you're a hero -- as happened to David Harlow and Jack Lockwood (two of the technical consultants to the film) at the 1991 Mt. Pinatubo eruption in the Philippines. But how unequivocally can you predict that eruption? If you predict it, and the town freaks, and nothing happens, you will destroy your reputation, potentially the town's reputation, certainly your agency's reputation, and you may end up killing people in an unnecessary panic.

You can see the problem, probably. You need to alert people when there is reason to alert them. You need to give people the best information you can, and make sure they understand it -- simply dumping it on them is unlikely to be a good thing, since most people just don't know how to interpret the potentially equivocal data. You need to take into account the potential harm to a town's economy and to the people's lives. And you sometimes need to do all this in an incredibly pressure-packed environment.

Doing all this takes fortitude, sensitivity, good judgement, and not a small amount of luck.

We had originally wanted to show the NOVA program on the Pinatubo eruption, but we were unable to get a copy quickly enough to show in class. It would have proven interesting for this assignment, because you could easily compare real life to the movies...oh well. But watch it if you ever have the chance. It is a fascinating story.

Incidentally, a couple people expressed surprise when they learned that Mammoth Lakes is in a volcanic region. It is indeed. Mammoth Mountain itself is a large ``plug dome'' built up of very viscous rhyodacitic lava (a composition between rhyolite, the lava with the highest silica content, and dacite, the next highest) from a series of eruptions between 50,000 and 220,000 years ago. It sits at the southern end of a belt of volcanic cones and lava flows which runs all the way up to Mono Lake east of Yosemite. But that's not the most important part: the Mammoth Lakes area sits inside a humungous volcanic caldera (a caldera is a crater more than 1 km in diameter), which is about 17 by 32 km in size and was formed in a huge eruption about 760,000 years ago. This is called the Long Valley Caldera. The most recent eruption near Mammoth Lakes was about 250 years ago, and even today there are still hot springs and other such activity.

In May 1980, there was a massive swarm of earthquakes, including four magnitude six earthquakes in less than 72 hours, near the southern edge of the Long Valley Caldera. This, coupled with information that an area in the center of the Caldera (called the ``resurgent dome'') was rising, got a lot of seismologists, volcanologists, and geologists worried. There was in fact an alert put out saying that an eruption was a distinct possibility. None happened, but unfortunately, the (distorted) word got out that Mammoth Lakes was going to be destroyed. Property values plummeted, and lots of economic trouble ensued for the town. Of course, the eruption didn't happen. Many of the people in the town harbor a lot of resentment toward the USGS as a result of the lost business and the stress they've been put through. Here are a couple of recent news stories from the local Mammoth paper, talking about the situation with the town and its reputation, published on 8 September 1996 and 16 February 1997, respectively.

The problem is that the area is still in a state of unrest, and eruptions will happen -- but volcanology is not yet in a state of being able to say when. Anyway, the point is that the 1980 thing mentioned in Dante's Peak really did happen -- one of the points of realism in the movie.

In case you are interested, here are some Mammoth Lakes references.

Part B: Did Dante's Peak do a good job of discussing these?

While I thought they really oversimplified these issues, if you gave me a reasoned answer either way, you got the full 10 points.

Part C: Volcanic and volcano-related phenomena in Dante's Peak

Dante's Peak showed lots and lots of different volcanic and related phenomena. I asked you to name five. Here's my (probably incomplete) list of the phenomena that I noticed, in no particular order:

I will only touch on the highlights. While earthquakes are a common accompaniment to volcanic eruptions, the size of the earthquake depicted in Dante's Peak during the first (phreatic) eruption is ridiculously large. Buildings don't collapse like the ones in the movie did without a magnitude 7 or so earthquake, but magnitude 7 earthquakes are (to my knowledge) unheard of during volcanic eruptions. The houses collapsing -- that's just Hollywood.

The lava flows really annoyed me. The lava shown in the movie (especially in the scene where they are in Grandma's cabin) is much, much too fluid to be erupted at Cascade volcanoes (with one very specific exception -- Newberry Caldera south of Bend, Oregon). The Cascade volcanoes are generated by subduction of the Juan de Fuca Plate under Washington, Oregon, and northern California, and have much more rhyolite, dacite, and andesite than they do basalt lava flows, like in the movie. It really annoyed me to have Hollywood jazz this up in such a dumb fashion - like the pyroclastic flow sequence was not good enough?

Incidentally, the scenes with Harry and his cohorts flying around in the helicopter around the lava dome were all filmed at Mt. St. Helens. Lava domes are typical in Cascade volcanoes, because the types of lava erupted in most Cascade volcanoes is pretty thick, gooey stuff, and tends to make domes pretty easily.

And here's what the USGS has to say about Harry's (Pierce Brosnan) attempt to drive across a lava flow:

A: No. Any attempt to drive across an active lava flow, even one that has partly solidified to form a thin crust, is likely to lead to disaster. With a temperature of 1,700 degrees Fahrenheit or higher, fresh lava will quickly melt rubber tires and ignite gas tanks. And if a vehicle gets stuck in moving lava, well, you know the rest of the story.
In other words, don't try this at home, kids.

Hot springs are common in volcanic areas, such as Mammoth Lakes, but while they can undergo changes in an eruption, they don't heat up like in the movie. You wouldn't get parboiled in seconds - you'd have plenty of time to notice it was hotter than usual and get the heck out. But of course the couple in the movie were having a quick tryst, and all disaster/horror movies are required to have the ``couple who messes around'' killed in some horrible way, so...

Carbon dioxide can actually kill trees and wildlife near volcanoes, even when they aren't in an active eruption. There are large areas in the Mammoth Lakes basin (south of Mammoth Mountain) where trees have died off due to high carbon dioxide levels in the ground. This is particularly prevalent near Horseshoe Lake.

While lakes in volcanic craters can be highly acidic, they don't eat aluminum boats or engines. And they don't change acidity anywhere near as quickly as in the movie. Plus the lake in the movie isn't even a crater lake. And the lake is acid enough to eat the boat and the boat's engine, but not to eat the flesh off the dead fish? All of this adds up to a big fat ``yeah, right, I don't think so.''

Now, this is not to say they didn't get somethings very right. I thought that the depictions of ashfall, landslides, lahars (which of course offs the boss who doubted Harry), and the pyroclastic flow at the end were pretty good, myself. Well, if you ignore the fact that pyroclastic flows move one whole hell of a lot faster than any Forest Service truck, anyway.

There certainly have been ashfalls similar to those shown when the dumbo wonder kids are driving up to Grandmas; for example, Yakima, WA was pretty well buried by ash after Mt. St. Helens blew. Lightning is a pretty common occurrence in volcanic eruptions, largely due to static electricity building up in the ash column. There is a really nice picture of volcanic lightning on the cover of the 28 February 1997 issue of Science; for those of you who don't have access to Science, there's another nice one below.

  Figure 1. Volcanic lightning generated during the 18 May 1991 eruption of Sakurajima Volcano in Japan.


Image by SVO.

Landslides along the sides of volcanoes are common occurrences. Lahars can be extremely dangerous and destructive, and are easily capable of taking out bridges as shown in the movie. Some lahars from Mt. Rainier have reached as far as Puget Sound, moving through what is now an area populated by close to 350,000 people. These mudflows are considered a major hazard at Mt. Rainier.

Pyroclastic flows are incredibly destructive and certainly capable of doing the sorts of damage they show in the movie. The lateral blast from Mt. St. Helens in the climactic 1980 eruption completely destroyed the forest north of the mountain for a range of up to 18 miles. These flows are highly dangerous -- if you're ever in an area where a pyroclastic flow is potentially going to happen shortly, get the hell out of there!

Overall, the movie was a balance of good stuff and some really awful stuff as far as the phenomena described in it.

Part D: What kind of lava is shown in the movie?

The lava in the movie is pahoehoe lava, very fluid and basaltic (remember that basaltic lavas are pretty unusual in Cascade eruptions). You can tell this especially clearly when it breaks down the wall in Grandma's cabin. However, I can see where you might have been confused when they tried to drive over the flow. In that scene, the lava looked pretty rough and blocky, and you could easily have mistaken it for a'a.

Because of this confusion, I just gave everyone 5 points for that question.

Part E: What is a phreatic eruption?

The folks at Volcano World have a good answer to this question.

Part F: What is a pyroclastic flow?

Again, Volcano World to the rescue! Here's their answer.

One sidelight, though. Pyroclastic flows can travel upwards of 200 km/hr. You can't outrun 'em and you can't outdrive 'em at those speeds. The movie got it wrong.

Part G: How many dead squirrels did the kids find, and did the dog live?

The kids found two dead squirrels on the trail to the hot springs, though Grandma said that dead ones were popping up all over the place. And yes, the damn dog lives.

Just for once, couldn't we have the damn dog die? I mean, the dog lives in every bloody disaster flick I've ever seen (and I've seen a lot of them). The damn dog even lives through the destruction of LA in Independence Day! (OK, so at least the aliens did us all a favor and got rid of LA, but still, couldn't they have also killed the damn dog?)

Where to go for more information

There are lots of good references for Dante's Peak-related stuff. Here's a few of the more interesting ones, but it's a very incomplete list:

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Greg Anderson
Sat Mar 15 19:39:56 PST 1997