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4.6

Some triggers give greater warning time for impending eruption than others.

Not all triggering events result in the immediate eruption of the impacted volcano.  In fact, the amount of time varies from almost instant result to a year or more.  Flank collapse usually occurs seconds before eruptions as in the 1980 eruption of Mt. Saint Helens.  Earthquakes can open cracks which take months for magma to travel through and cause eruptions much delayed from the actual trigger.

It is possible in some cases to detect and predict when the failures will occur.  Instability, which may cause a flank collapse, can be measured and recorded to determine a potential failure point.  At Mt. Saint Helens, a large bulge was monitored for several weeks prior to the flank collapse which occurred there.  Growth rates of up to 7 feet per day were measured implying that the slope would quickly become unstable.  It took a month of this growth to reach a point  where it was ready to fail and an earthquake pushed it past the breaking point.  Also, rainfall and glacial melt rates can be monitored to estimate pore water pressure increases in volcanic surfaces.  It is important to remember, however, that Mt. Saint Helens is only one case, and it occurred in an area easily accessible to scientists. Some volcanoes are remote and minimal resources are devoted to their monitoring meaning a collapse or other trigger could occur with little or no warning.

Earthquake impacts can  be instant (the collapse above was triggered by an earthquake beneath the volcano), or they can take months before an eruption occurs. Volcanic and tectonic earthquakes can encourage magma mixing and instability. Despite scientists best efforts, the moment of eruption is often unpredictable and estimations of when an eruption will occur may only be accurate to days, or months.  As scientific methods and technology continue to improve, eruption prediction is becoming more and more feasible and accurate.  Some volcanologists speculate that as many as 50% of eruptions can be predicted accurately and many more can be forecast within a reasonable time to initiate warnings and evacuations.  Much is this is influenced by the study of volcanic triggers.  For more information on eruption prediction click Here.

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