"One big 'Aha!' for geologists was that an entire mountain could collapse." (Peter Frenzen) "Mount St. Helens certainly reminds us of the power of nature, and we can certainly see that in the evidence of the 1980 eruption that's all around us. And here we just have an opportunity to see sort of another chapter in its history and to understand the forces that lie beneath our feet." (Peter Frenzen) In 1980, the United States suffered the deadliest and most destructive volcanic eruption in its history when Mount St. Helens literally blew its lid off, the result of seismic activity during the eruption. What made the eruption all the more remarkable was that a fair amount of preparations had gone into anticipating it, after an earthquake in the area a few months earlier alerted federal geologists to the possibility of activity there. In fact, Mount St. Helens had been the cause of the earthquake itself, the result of its own lava flows under the surface.