If you look at almost any volcano, it might have a bout of eruption for days to months at a time, then go quiet for decades, centuries or more. So when you think about the activity at any given volcano, you should not only concern yourself with what might be happening when the volcano is actually coughing stuff up (erupting), but also when, at the surface, things look perfectly calm.
Mount St. Helens Is Recharging Its Magma Stores
