1. Provide an appropriate introduction to plate tectonics and volcanic activity. The following is a suggested introduction.
The most important geological phenomena, volcanoes and earthquakes, occur because the earth’s crust is broken into eleven large and five smaller tectonic plates that move relative to each other. This happens in geological timescale, from thousands to millions of years. Because each of the tectonic plates move in relation to those surrounding them, there are three possible types of boundaries between plates: (1) convergent boundaries where the plates move towards each other with the plates grinding against one another or one plate overriding the other; (2) divergent boundaries in which the plates move apart and separate; and (3) transverse boundaries in which tectonic plates slide past each other without separating or overriding. The areas near these borders are prone to geological activity; however, in some locations, volcanoes can occur in the middle of a plate, over what is called a hot spot. The Hawaiian islands are located over a hot spot in the middle of the Pacific Plate.
Subduction zones are those parts of a convergent boundary in which one plate is being pushed under the Earth’s surface by another plate, which rises up or folds onto itself, lifting up the land. The energy accumulated by this process in the form of tension on the edges of the plates builds up and is often released in sudden bursts of energy. The resulting shock waves are called earthquakes. The long-term result of this process can be a ridge of islands on the ocean floor or a mountain chain on the land.
The movement along transverse boundaries, in which plates slide past each other is not smooth either. Tension builds up as the pressure for movement increases on rocks that are holding movement back. Suddenly, there is a fracture and the release of energy causes an earthquake. Along the boundaries where the plates move apart, divergent boundaries, there are earthquakes too, but they are significantly weaker because the shock waves are caused by superficial fractures in the surface of the earth as it stretches above the separating plates.
Volcanoes form when the hot molten rock from the interior of the earth, known as magma, on which the plates float, finds a way to the surface through the cracks and seams that are produced by tectonic plate movement. The mechanisms are different, and so are the resulting eruptions. It is even hypothesized that it is the magma pushing upwards that drives the motion of the earth’s tectonic plates. Volcanoes form along convergent and divergent boundaries. Transverse boundaries, where the plates slide past each other, do not generally cause volcanoes.
A volcano is usually depicted as a cone-shaped mountain with a crater at its top. But there are a variety of shapes that volcanoes can take. They range from the steepest cones that are produced by the most explosive eruptions and formed by the piling up of cinderlike materials, to the broad shield cones with gentle slopes made up of solidified lava from very fluid flows that can travel for hundreds of miles.
Los Angeles lies near a border zone between tectonic plates that are sliding past each other. The city is moving in a northwest direction relative to San Francisco at a speed of 5 centimeters per year along what is known as the San Andreas Fault. This sliding does not happen smoothly, and rock is twisted and torn, resulting in earthquakes too, but volcanoes are unlikely.
The strength or intensity of a volcano is measured in a scale called the Volcanic Explosivity Index which runs from 0 to 8, with 0 being non-explosive and 8 being mega-colossal, the type of explosion that created the Yellow Stone Caldera in Yellow Stone National Park. The caldera measures 34 miles (55 km) by 45 miles (72 km).
2. Introduce segment #1 by providing the following introduction to the movie:
Dr. Amy Barnes, a geologist, is asked to come to Los Angeles to provide scientific advice on an earthquake and the unusual deaths of seven city workers from excessive heat underground. This scene begins in the LA City emergency management center. As the scene opens Dr. Barnes is arguing with Stan, an official of the Metropolitan Transit Authority (MTA) the agency that runs subways in the city. MacArthur Park is a large park near downtown Los Angeles. This segment shows the conversations between Dr. Barnes, Stan, and city emergency management director, Mike Roark. The scene then shifts to MacArthur Park where Dr. Barnes and Mr. Roark continue their discussion. Note that Dr. Barnes says something about certainty. We’ll talk about what she says later.
3. Play segment #1, the conversations between the city officials and the scientists. This will take approximately 4 minutes.
4. Engage students in a class discussion. First, ask why Dr. Barnes was unwilling to state with any certainty that a disaster would happen. The conversation should include the following concepts: (1) she only had early warning signs and (2) scientists don’t talk about certainty; even well-established scientific theories are considered subject to being challenged by experimentation and later discoveries.
Then turn the discussion to the practicalities of the situation faced by Rourk early in the film, before it was clear that a disaster had struck. Ask the class to provide relevant factors that city officials would have to consider in determining whether to take action in a situation in which there were only early warning signs of a possible problem and no certainty that the unusual events were the beginning of something catastrophic. Write a short title for any appropriate comments on the board. The list should include, at least:
a. Cost to the city government of emergency actions (such as calling out police to manage an evacuation);
b. Economic and personal costs of the disruption (businesses will lose money; people who depend on subway service to get around will be inconvenienced; children who can’t be picked up from day care on a timely basis will be upset, etc.);
c. Risk of not calling for such actions (cost in human lives and property damage if the feared catastrophe ensues);
d. Degree of certainty necessary to justify emergency actions;
e. Whether excessive caution could be counterproductive (for example, making it less likely that the public will react positively in the next emergency if this turns out to be a false alarm); and
f. Whether a low likelihood is equivalent to impossibility.
At the conclusion of the discussion, describe for the class the following example of effective risk management and cooperative communication between scientists and authorities. In 1991, nearly 75,000 people were evacuated before the eruption of the Pinatubo Volcano in the Philippines. Experts estimate that the timely evacuation saved between 5,000 and 20,000 lives and prevented at least $350,000,000 in property losses. A large U.S. Air Force base was heavily damaged in the eruption, but due to the prediction and prompt action by the Air Force, the planes and some expensive machinery were moved to another location before the eruption.
5. Discuss briefly the two warning signs that emerged in the segment: (1) heating of underground pipes and of the water in the lake at MacArthur Park, and (2) small earthquakes (tremors). It is a popular belief that animals, and particularly birds, are the first to notice such tremors and to flee. Not depicted in the movie are other effects that forecast an upcoming eruption, such as the release of sulfur dioxide gas that could also contaminate underground water and the bulging of the ground as magma pushes toward the surface. At high altitudes melting snow and ice can also be a sign of hot magma coming closer to the surface. All these effects can be monitored and detected by scientific instruments, sometimes years in advance. However, precise forecasting is still a major challenge for scientists and may never be achieved in full.
6. Introduce the typical locations of volcanoes in relation to tectonics and plate subduction zones. See Plate Tectonics and the “Ring of Fire” from the USGS.
7. Discuss the historical event of Paricutín, Mexico, mentioned by Dr. Barnes’ assistant in the movie.
8. Introduce segment #2 by telling the class that Dr. Barnes has been exploring underground tunnels with her assistant who fell down a chasm into lava and died.
9. Play segment #2 in which lava eruptions, ash clouds and volcanic bombs cause havoc in Los Angeles. Ask students to note down in two columns which effects shown are realistic and which they consider creations of the filmmakers.
10. Once the segment is completed, make a single list on the board of the four volcanic effects shown in the movie. Note that all effects are realistic, just not at this rapid succession and not all in one volcanic eruption of a single kind. Volcanic bombs are associated with more explosive eruptions. The very fluid lava, on the other hand, corresponds to gentle eruptions of the Hawaiian type (VEI 0-1)
11. Ask students to point out similarities and differences between the situation depicted in the movie and the historical event of Paricutín. The discussion should include the following points: The eruption in Paricutín occurred in a rural area where light tremors and the possible heating of groundwater would go unnoticed. The eruption was discovered when the ground opened and lava started to pour out. In the movie, underground heating affected pipes and caused burn injuries in workers before a volcanic eruption was considered as a possibility. On the other hand, in both instances, the eruption happened in unexpected locations where no previous eruptions had taken place and the whole process, from the first signs of lava to the formation of a large volcanic cone, could be witnessed and monitored by the population and scientists alike. In Paricutín, as in almost every other volcanic eruption, the lava could not be stopped and the village was covered under a thick layer of lava, above which only the famous church spire remains visible.
12. This step may occur at any point after Step #10 and after the class has had an opportunity to do the Homework Assignment found below. Decide upon an appropriate class activity so that all students will benefit from what students in the various groups have learned through their homework assignments. Steps 13 – 17 should not take more than about 20 minutes. For example, you can have one student from each numbered homework group give a 3-minute report on what was learned in the homework assignment. You can have the students from each numbed group caucus for a few minutes and then present a short report on what they learned in the assignment. If there isn’t time, this step, or any of the others, can be eliminated.
13. Help students classify the four volcanic effects referred to in the introduction and seen in the film into two columns, one for each type of eruption: explosive eruptions and gentle eruptions: