When a strong earthquake triggered Mount St. Helens’s colossal volcanic explosion on May 18, 1980, the blast obliterated every object within a six-mile radius. It remains the United States’s most powerful, and the world’s fifth most destructive, volcanic event in recent history. Here are more facts to mark the 40th anniversary of the Mount St. Helens eruption. 

1. Mount St. Helens is part of the Pacific Ring of Fire.

Mount St. Helens is part of the chain of 160 active volcanoes around the Pacific Rim known as the Ring of Fire. It sits on top of the subduction zone where the oceanic Juan de Fuca tectonic plate slips under the North American plate. It’s a stratovolcano, also known as a composite volcano: a steep-sided volcano with a cone made up of layers of lava, ash, and debris. Stratovolcanoes are considered more dangerous than shield volcanoes, which are created by slow lava flows and feature more gentle slopes. (The Hawaiian islands are a chain of shield volcanoes.) Stratovolcanoes tend to erupt explosively, and their steep sides are prone to landslides, avalanches, and sometimes even collapse.

2. Mount St. Helens was named for a British diplomat.

Mount St. Helens as it appeared before the May 18, 1980 eruption.Rick Hoblitt, USGS // Public Domain

Mount St. Helens isn’t named after a saint—it was named by George Vancouver, the British naval explorer who charted the Pacific Northwest in the 1790s, for his friend, Baron St Helens. The baron, whose given name was Alleyne Fitzherbert, served as a diplomat for the British government in Brussels, Paris, Russia, Spain, and elsewhere. Among some of the indigenous people of the Pacific Northwest, the volcano is known as Louwala-Clough (Smoking Mountain), Lawetlat’la (Smoker), and Nsh' Ak'w (Water Coming Out).

3. Mount St. Helens has been erupting for a long, long time.

Mount St. Helens has gone through a number of eruptive stages over its lifetime, beginning 275,000 years ago. That’s relatively young for a volcano—a number of volcanoes formed by the Hawaiian hot spot are tens of millions of years old. However, volcanoes change drastically over their lifetimes: Most of the modern Mount St. Helens cone that is visible now formed during the last 3000 years, according to the U.S. Geological Survey.

4. Mount St. Helens is the most active volcano in the Cascade Range.

Mount Baker, Mount Shasta, Mount Rainier, Mount Hood, Glacier Peak, and Lassen Peak are also active volcanoes in the Cascades, but the most recent activity among them was at Lassen Peak in the early 1900s. Mount St. Helens is the youngest among the Cascade volcanoes, too, which is why it shows fewer signs of erosion than neighbors like Mount Rainier or Mount Hood.

5. The cataclysmic 1980 explosion of Mount St. Helens was the volcano’s first major eruption in more than 100 years.

Mount St. Helens erupts on May 18, 1980.Robert Krimmel, USGS // Public Domain

Prior to 1980, the last major explosive eruption of Mount St. Helens on record occurred in 1800. There were several minor explosions throughout the early 19th century up until 1857, when the volcano became dormant once again. This period of volcanic activity created what became known as the Goat Rocks Dome, which was part of Mount St. Helens’s distinctive silhouette until it was destroyed in the 1980 eruption.

6. The 1980 Mount St. Helens eruption is still the most powerful volcanic eruption in U.S. history.

On the morning of May 18, 1980, a 5.1-magnitude earthquake caused a massive landslide—the largest debris avalanche in history—on the north face of Mount St. Helens. In the volcanic eruption that followed, the lateral blast destroyed every living and non-living thing within six miles of the volcano. The deadly pyroclastic surge—a fast-moving, super-hot cloud of ash, rock, and volcanic gas—traveled as much 18 miles away from the blast. The hot lava, gas, and debris mixed with melting snow and ice to form massive volcanic mudflows that surged down into valleys with enough force to rip trees from the ground, flatten homes, and completely destroy roads and bridges. Rivers rose rapidly, flooding surrounding valleys. Ash fell from the sky as far away as the Great Plains. Two-hundred-and-fifty miles away, ash blanketed Spokane, Washington, in complete darkness.

7. A Mount St. Helens volcanologist likely saved hundreds of lives.

Fifty-seven people died as a result of the eruption, though the number could have been much higher. Volcanologist David Johnston was an advocate for restricting access to the volcano when, in early 1980, an increase in seismic activity signaled that an eruption might be imminent. Johnston died when the observation post from which he was monitoring Mount St. Helens was destroyed. “The volcano-monitoring effort of which Dave was part helped persuade the authorities first to limit access to the area around the volcano, and then to resist heavy pressure to reopen it, thereby holding the May 18 death toll to a few tens instead of hundreds or thousands,” according to the authors of the 1982 U.S. Geological Survey professional paper about the disaster.

8. The eruption changed the appearance of Mount St. Helens forever.

Prior to the 1980 eruption, Mount St. Helens had a symmetrical, snow-covered cone that gave it the nickname the “Mount Fuji of America.” The peak stood 9677 feet tall. But the lateral blast changed its appearance considerably: The top 1300 feet of the summit was destroyed by the eruption and landslide. Now, the volcano sports a north-facing, horseshoe-shaped crater that contains a lava dome and a glacier.

9. Mount St. Helens was made into a national volcanic monument in 1982.

Ash from the May 18, 1980 eruption of Mount St. Helens covers the ground at a farm located 180 miles from the volcano.Lyn Topinka, USGS // Public Domain

Two years after the devastating eruption, Congress turned the area around Mount St. Helens into a 110,000-acre national volcanic monument for research and recreation. Located within the Gifford Pinchot National Forest, it’s managed by the U.S. Forest Service. Visitors can hike, camp, fish, and more, though hikers need a special permit to climb up to the summit. (This isn't permitted when the volcano is experiencingunusually high activity, of course.) They can also tour the Johnston Ridge volcanic observatory and Ape Cave, a lava tube formed almost 2000 years ago.

10. Mount St. Helens has been shrinking.

A 1982 survey measured the summit of the volcano at 8365 feet tall. As of 2009, it measured 8330 feet. The shrinkage is probably the result of erosion and collapses of crater walls.

11. Mount St. Helens is not done erupting.

The U.S. Geological Survey still rates Mount St. Helens’s threat potential as “very high” because of the potential for eruptions and the number of nearby communities that those eruptions could impact. The volcano is just over 50 miles from Portland, Oregon, and less than 100 miles from Seattle. The 1980 eruption destroyed all structures around the nearby tourist destination of Spirit Lake, including more than 200 houses and cabins. Mount St. Helens’s most recent volcanic activity stretched from 2004 to 2008, during which the volcano grew a new lava dome and periodically released plumes of steam and ash. There were few significant explosions before the volcanic activity died down in 2008.

While the U.S. Geological survey warns that Mount St. Helens will likely explode again during our lifetimes, the agency predicts that an explosion of the magnitude of the 1980 eruption is unlikely. However, scientists from the U.S. Geological Survey Cascades Volcano Observatory and the Pacific Northwest Seismic Network carefully monitor seismic data, gas emissions, changes in the ground surface, and other factors around Mount St. Helens to forecast potential volcanic activity.