When Science Goes Wrong by Simon Levay Page A

visited the caldera in 1988, they did not descend into the central crater, because it would have meant death to do so: the crater floor was incandescent with heat. Obviously, something very serious was going on inside Galeras. They returned to Pasto and reported their findings to the director of the Colombian National Institute of Geology and Mines, or INGEOMINAS. He called in turn for help from the United States. A few weeks later, David Harlow, of the US Geological Survey (USGS) in Menlo Park, California, brought a small team of scientists to Galeras. They installed several more seismographs around the volcano.
    In the spring of 1989, a larger group of Colombian and foreign volcanologists met in Pasto. Two eruptions took place that spring, and though they had both been very small, they got the attention of the people of Pasto. The local government began issuing colour-coded warnings, and as so often happens, these induced more confusion than comprehension. Furthermore, the city experienced serious economic problems, as banks stopped issuing loans to local businesses and tourism dried up.
    Soon after the 1989 meeting, Galeras quieted down. Then, in the autumn of 1991, eruptions began again. A lava dome rose slowly from the floor of the crater, eventually reaching a height of 150ft. In response to this alarming development, the governor of Nariño called for yet another meeting of scientists, which took place later that month. Among the attendees was Marta Calvache, a young Colombian volcanologist who grew up in the shadow of Galeras and who had been at Nevado del Ruiz during the deadly 1985 eruption. In the aftermath of that event she had met Stanley Williams, an expert in volcanic gases at Louisiana State University. Calvache later went to LSU and did a master’s thesis with Williams. (Williams moved to Arizona State University in 1991.) The relationship between Calvache and Williams was an obvious and immediate benefit to Calvache, furthering her expertise and her career. But, as it turned out much later, it was an even greater benefit to Williams, for it was Calvache who saved his life while his colleagues died.
    Another attendee at the 1991 meeting was Bernard Chouet, a Swiss-born geophysicist with the USGS in Menlo Park. Chouet’s speciality was the interpretation of the seismic signals emitted by active volcanoes. Over the course of a few years before the meeting, Chouet had come to believe that he had discovered a hitherto unknown method for using these signals to predict eruptions.
    The seismic signals generated by volcanoes are of two basic kinds. The more common kind are basically little earthquakes: they are produced by the fracturing of rock as magma creates passageways for its ascent to the surface. On seismograms, these events look quite like the common, nonvolcanic earthquakes that are generated by the motion of geological faults: brief, jittery signals that, if sped up and played through a loudspeaker, sound like bangs, pops, rips, crunches, roars or other unattractive noises. They are assigned magnitudes just like regular earthquakes and, though most are tiny, a few range up to magnitude 5 or so, and are thus easily felt by people living in the vicinity of the volcano. They are called volcano-tectonic earthquakes.
    The other, less common seismic signals are quite different. They are low-pitched (infrasonic) vibrations that may continue for half a minute or longer. When sped up and converted into sound, they have an eerily musical quality – they may be reminiscent of whale song, a dirge played on trombones, or Tuvan throat-singing.* Unlike volcano-tectonic earthquakes, these events confine most of their energy to a single, very low frequency – a deep-pitched tone – along with some higher-pitched harmonics that add to the musical quality of the sound. They are called long-period events – ‘long-period’ in this context means the same thing as ‘low-pitched’.
    Prior to Chouet’s work, much more