41st anniversary of Mount St. Helens eruption spotlights improvements in volcano monitoring 41st anniversary of Mt. St. Helens eruption spotlights improvements in volcano monitoring Tuesday marks the 41st anniversary of the deadly Mount St. Helens eruption. Since then, scientists have taken big steps in monitoring volcanoes. SEATTLE - Tuesday marks the 41st anniversary of the deadly Mt. St. Helens eruption. Since then, scientists have taken big steps in monitoring volcanoes. Of call the Cascade volcanoes, Mt. St. Helens is monitored the closest. "Just based on its history of being so active recently, we would expect it will most likely be active again in the near future," said Cascades Volcano Observatory research geologist Emily Johnson.