Previous bad eruption calls are the main reason that Harry's boss, Paul, is so worried about a wrong call. He mentions that in 1980 he was sure that Mammoth Mountain was going to erupt, which it didn't, but the tourism and everything of the town was destroyed due to the bad call. As previously listed that was one of the worse case scenarios.
Mammoth Mountain is a real volcano located within the Long Valley Caldera of California. It is similar in composition to Mount St. Helens except that it has more of a basaltic magma (Oregon State). Most scientists figured that if the mountain were to erupt that the resulting eruption would be extremely minor. In 1980 the region was hit with four magnitude 6 earthquakes along with 25 cm of dome uplift of the caldera floor. In recent years more activity followed with groups of trees being killed (pictured in the CO2 Gas Levels section above) and more gas emissions (USGS). So it seemed likely that an eruption was possible in 1980, but I can find nothing about any evacuation of the region around that time.I have been "recently" contacted by a couple of people (Micah Kipple and Craig Jones) commenting on my analysis of Mammoth Lakes so I figured I would go ahead and update that information. I may have been unclear before but in the movie it was never mentioned that an evacuation of Mammoth Lakes was called for. What is said is that Paul was in talks with the USGS in 1980 for a possible alert of the town when word was leaked that the USGS expressed concern so tourists stopped showing up and the town went bankrupt. This caused him to be much more cautious when it comes to putting a town on alert.
On the real life side of things, I was presented with more information regarding the possible alert that the USGS was actually putting on Mammoth Mountain (thanks Craig). One of my previous problems was that the year was wrong, which didn't help my search before. It turns out that the earthquakes under the mountain started in 1978 and continued through 1982 when the possibility of an alert by the USGS was discussed (Kerr, 1982). The USGS was in initial talks about the alert and didn't get the local government involved yet. The main problem was that the alert was leaked out by a reporter for the LA Times, who released the information just before the Memorial Day weekend causing concern before a local festival (The Free Library). This caused anger among the town's government who felt blindsided and caused tourism to decline rapidly. After the leaked story the USGS quickly issued their own alert, a notice of potential volcanic hazards, the lowest alert level (USGS Open-File Report 82-583, "Preliminary assessment of potential volcanic hazards in the Long Valley-Mono Lake area," by C. Dan Miller et al.), which described potential volcanic hazards and areas that could be effected. The alert levels increased as more earthquakes hit the town in 1983 but the mountain never erupted and it took the town several years to recover, all the while never forgiving the geologists who ruined their town. This event made the USGS rethink how they would issue alerts on volcanoes and dropped the system they were using shortly after in 1983 (NY Times).
Another problem that was pointed out to me from this post where I state:
Previously mentioned in the movie are laser beams that measure the amount of growth on the volcano. This can be produced in 2 ways. One is uplift of the crater floor and the other is actually producing what is called a lava dome. The growth of the crater bottom is also called bulging or swelling and lasers are not typically used in measuring this. Usually what is used is Electron Distance Meters (EDM), which uses infrared to bounce a beam off of the ground. This measures the change in distance between the sensor and the crater surface, similar to a laser but not quite. Some other methods include GPS which also can measure the change in height and tiltmeters which measure the change in angle of the surface (AVO).I wanted to make a clarification point that was mentioned to me in an email by Micah Kipple. The crater floor is not the only part of the volcano that is being measure but most of the measurements are actually made on the flanks of the volcano. Not only are those areas easier to get to, provide a larger surface area to monitor, for could potentially give you safer and just as reliable results.
Thanks to both Micah and Craig for bringing this to my attention and I welcome anyone else who finds out something I missed or made a mistake on to contact me with the correct information.