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4.5

Eruption prediction is complicated by the complexity of triggering events.

In order to better understand when a volcano might erupt, it is critical to examine all of the possible triggers of each volcano independently. This is mostly accomplished through volcanic monitoring and the study of previous eruptions. Volcanic monitoring techniques are covered in-depth in Big Idea #10.  Monitoring can be done on site or through remote sensing techniques using satellites. Much can be learned from studying past eruptions also. By examining ash and lava flow deposits, a volcanologist can get a good understanding of magma composition and average time between eruptions. Study may implicate a certain triggering event is more common than others at a specific volcano as well.

It is also important to consider non volcanic triggers which may often be overlooked by a volcanologist solely concerned with the geology of the system.  A major factor in volcano destabilization can be the addition of pore water pressure to a slope.  This results most dramatically from glacial or snow-cap melt triggered by a rising magma body.  Read more about this Here.  This is an area which requires interdisciplinary knowledge since volcanologists may not have a good understanding of groundwater properties and slope stability.  To fully understand volcanic triggers requires knowledge of volcanic geology, earthquakes and seismicity, slope stability, groundwater flow and properties, climate and weather, fluid mechanics, physics, chemistry, and other more scientific fields.  There is also a great deal required in social and cultural understanding when working with local populations on monitoring, warning, and evacuation procedures.  Since it is impossible for one person to grasp all of these concepts, communication between scientists is critical in proper event prediction or forecasting.

The case of Mt. Saint Helens has been explored in depth in this Big Idea and fits into this sub-idea as well.  Close monitoring began months before the eruption occurred as internal earthquakes signaled the mobilization of magma.  As this magma moved toward the surface, the surface bulged and it was clear to volcanologists that the volcano was becoming unstable and nearing eruption.  The surrounding area was evacuated under the assumption of local residents that the volcano would erupt very soon. After a month with no major eruption, and a few weeks of quiet from the volcano, some returned home to gather belongings despite warnings from scientists that the volcano was still unstable.  The following day (May 18, 1980) an earthquake inside of the volcano triggered the flank collapse and within seconds the eruption of Mt. Saint Helens.  Another escort of residents to their homes was planned for later that day. Despite intense monitoring by experts throughout the world, the eruption could not be predicted to within a time frame acceptable to the general population and in this case it resulted in the loss of 57 lives.  Many triggers cannot be predicted with enough time to evacuate or they may take too long to keep an area evacuated completely.  For a complete log of the events leading up to the eruption read the USGS page Here.

This does not mean, however, that volcanic eruptions cannot be predicted.  Eruptions at the volcano Hekla in Iceland can be predicted within minutes.  In 2000, volcanic precursors were noted by volcanologists and a warning was given that the volcano would erupt in 15 minutes.  17 minutes later a moderate sized eruption occurred. This case is not because of volcanic triggers, but instead volcanic precursors such as micrseismic earthquakes (very small magnitude earthquakes inside of the volcano).  Read more about eruption forecasting and Hekla Here.

2000 eruption of Hekla, Iceland with ash cloud rising 13km which was predicted successfully.

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