Great but difficult question.

Volcanoes rarely form and become extinct in one eruption, rather they are formed through sequences of eruptive cycles over thousands to millions of year.

Just like a book is made of many pages, volcanoes are built through many eruptions. If you open a book at random, what are the chances that it opens to the last page? Very low. More likely you pick a page somewhere within the book, meaning that many more pages follow. By the same token, what are the chances that Mount St. Helens' most recent eruption was its last? Most volcanologists would say, very low.

So, it's almost certain that Mount St. Helens (MSH) will erupt again. The question is when? That's tough to predict. Part of the problem is the shortness of the human lifespan compared to the time it takes for most geological phenomena to occur. As people, we'd be really worried if it was certain that a volcano was going to form in our neighborhood sometime over the next 20 years; we'd worry less if we knew that this would happen sometime in the next million years. Nature doesn't care whether the eruption happens tomorrow, or 100,000 years from now--but to people, the timing makes a huge difference.

Scientists consider another eruption of MSH in the next century likely enough that they're actively monitoring it, searching for signs of eminent danger. So...the probability that MSH will "explode again" is almost 100%. What we'd like a better understanding of is when that explosion is going to happen. Regrettably, we're a long way away from making such predictions accurately, just as we are with predicting earthquakes.

Stay curious!

There is currently no way to predict a volcanic eruption. Volcanologists can "forecast" an eruption, but with a LOT less accuracy than a weatherman (yeah, it's really, REALLY hard). You're probably thinking about the famous 1980 eruption of Mt. St. Helens. But, did you know there's been a LOT of activity on Mt. St. Helens since then? Since May 1980, there have been both explosive & non-explosive eruptions at Mt. St. Helens (the explosiveness of an eruptions is controlled by many factors, the most important of which is the amount of dissolved gases in the magma). In fact, from 2004 - 2008, Mt. St. Helens was erupting, and most people didn't even notice! There's a lava dome that's slowly growing inside of the Mt. St. Helens crater, and as of 2013, the crater has been ~7% filled with lava.

Mt. St. Helens also has a volcano monitoring network ( here ) that measures earthquakes, gas flux from the volcano, and ground deformation. Generally, an increase in these measurements could indicate an increase in eruptive activity. But, even with all of that equipment, it's impossible to tell exactly what's going on underneath the volcano.

Most of the volcano "forecasting" techniques we volcanologists have learned come from actively erupting volcanoes (e.g., Etna or Kilauea) - although Mt. St. Helens is active, it's not actively erupting. This makes it hard for us to understand what certain signals underneath the ground mean - it's like being blind and trying to learn what things look like without being able to touch them.

Rest assured, the USGS is well on watch at Mt St Helens (and the 50+ other volcanoes we have in the US)! You can watch too, if you'd like - the US Forest Service has a 'VolcanoCam' that looks at the MSH crater: ( watch here ), or you can find more information on Mt. St. Helens at Mt. St. Helens .

I hope this has answered your question, and that you continue to find volcanoes just as fascinating as I do!

Another eruption by Mount St. Helens is likely, some would say essentially guaranteed, but an exact number cannot be assigned. A change in seismic activity often indicates a start to new activity, so scientists are continually monitoring such events occurring in the vicinity of Mt. St. Helens.

Besides Mount St. Helens, many other volcanoes in the Cascade mountain range of the US Pacific Northwest could potentially erupt, such as Mount Hood and Mount Rainier.

Yes, it is extremely likely that Mt. St. Helens will erupt again. The average eruption recurrence interval is every 100-300 years. No, this eruption will have little or no effect on the likelihood of an eruption of the nearby volcanoes, which have not erupted in historic times.

We're reasonably sure that Mount St. Helens will erupt again and will do so explosively, since it has done so many times in the past and shows no signs of becoming inactive. We know that Mount St. Helens, like other volcanoes of its type, will give us plenty of warning in the form of earthquakes and possibly also changes in the shape of the mountain before it undergoes another major eruption, and the National Park Service has teams of geologists monitoring it continually to give us as much warning as possible. As such, we know that no large eruption is imminent, but beyond that, all we can say is that sooner or later it will happen again.