Mount St. Helens, a prominent stratovolcano in the Cascade Range, stands as a powerful symbol of geological change in the Pacific Northwest. The volcano is part of the Pacific Ring of Fire, a zone known for frequent seismic and volcanic activity. Its catastrophic eruption on May 18, 1980, marked a significant geological event, drastically reshaping the landscape and the mountain itself.
Before the Eruption
Prior to the 1980 eruption, Mount St. Helens boasted a majestic, symmetrical cone, often earning it the nickname “Fujiyama of America.” Its summit reached an elevation of 9,677 feet (2,950 meters). The mountain’s pristine appearance had been largely shaped during the Kalama eruptive period, which occurred between A.D. 1479 and 1720. This period saw Mount St. Helens gain approximately 1,000 feet of elevation, contributing to its iconic pre-1980 form.
The May 1980 Eruption and Its Impact
The dramatic change to Mount St. Helens’ height occurred on May 18, 1980, when a magnitude 5.1 earthquake triggered a catastrophic sequence of events. The earthquake caused the entire northern flank of the mountain to collapse in a massive landslide, recognized as the largest subaerial landslide in recorded history. This immense structural failure effectively removed the upper portion of the volcano. The sudden removal of this overlying material rapidly depressurized the volcano’s internal magma system.
This sudden pressure release led to a powerful lateral blast, which surged horizontally from the mountain’s side. The blast consisted of superheated volcanic gases, ash, and pulverized rock, traveling at speeds that outran the initial landslide. The combination of the landslide and the lateral blast removed approximately 1,300 to 1,370 feet (396 to 400 meters) from the mountain’s summit. This event transformed Mount St. Helens from a symmetrical cone into a mountain with a colossal, horseshoe-shaped crater opening to the north.
Mt. St. Helens Today
Following the dramatic 1980 eruption, Mount St. Helens now stands at an elevation of approximately 8,363 to 8,366 feet (2,549 to 2,550 meters). The mountain’s profile is distinctly different, characterized by the large horseshoe-shaped crater that resulted from the collapse of its northern flank. Within this immense crater, a new lava dome has been forming and continues to grow.
While the dome has undergone periods of growth, its steep sides tend to crumble, which can result in a reduction of its overall height over time. Mount St. Helens remains the most active volcano in the Cascade Range, and ongoing monitoring efforts track its seismic activity and any changes in the lava dome.