Our studies tell us a lot about how Mount Shasta has behaved in the past, going back as far as an older volcano that was destroyed by an enormous landslide about 300,000 years ago and coming up to our own experiences of recent debris flows. Have we come to some conclusions about whether Mount Shasta is dangerous? Yes, we have.

It seems fair to assume that Mount Shasta's most likely future activity will be similar to its past behavior. We know that it has undergone periods of major cone building; these were periods of nearly continuous lava-flow eruptions and associated explosive and other disruptive events that lasted for centuries or millennia. If some of these events were to occur in the future, they are likely to affect nearby communities, air routes and other transportation corridors in the area, and rivers that head on the volcano. Clearly, future eruptions pose a potential danger to people. We also know the volcano generates debris flows every now and then and these are capable of causing serious damage along streams draining the volcano even without an eruption. At the same time, we think that repetition of the most drastic past event that we know about—a catastrophic landslide that destroyed ancestral Mount Shasta—while possible, is rather unlikely.

Finally, we know that Mount Shasta is an active volcano—it erupted only about 200 years ago and has erupted many times in the past few thousand years. According to our studies, the volcano has erupted on average at least once every 600 years in the past 4,500 years. With such an active record of recent volcanism, we have every reason to think it will erupt again.

We can use the knowledge gained from our studies at Mount Shasta to estimate the probabilities that certain types of events will occur again in the near future. Probabilities can be used for making decisions about land use, insurance, and other long-term needs. Based on the geologic mapping of the volcano, we've prepared hazard-zonation maps that identify areas most likely to be affected by different types of volcanic activity (see examples for Mount Shasta and other volcanoes). These maps can help people and emergency-response professionals plan how to respond to renewed activity of the volcano (learn more about basic elements of a response plan).

Monitoring of the volcano by USGS scientists can detect signs that the volcanic system gives about impending changes–things like swarms of earthquakes, deformation of the ground surface, or changes in the composition of fumaroles or ground water (learn more about volcano-monitoring techniques). Armed with these types of information, the citizens of Mount Shasta's surrounding communities and the authorities responsible for managing the land resources or maintaining the infrastructure of modern transportation, communications, and emergency-response planning can be informed about activity at Mount Shasta to help them make wise decisions, both for the long range and in the event of a return to activity by the largest stratocone volcano in the Cascade Range.