This eruption has a VEI of 5. The observations you just read describe Mount St. Helens when it erupted on May 18, 1980. It's also the most extensively studied eruption of any in the world to date.
Scientists glean clues to the volcano's future behavior by analyzing the past.
Mount St. Helens alternates between eruptive periods and dormant periods. During its most recent eruptive period in the 1800's, a major explosive eruption was followed by relatively smaller eruptions over the next 57 years. Assuming that Mount St. Helens behaves in the same way, the present eruptive period could continue for years. However, the volcano's past history suggests that a similar eruption might occur before the volcano returns to a dormant period.