This week marks the 40th anniversary of the Mount St. Helens volcanic eruption in southwestern Washington. According to NASA, small earthquakes beginning in mid-March marked the beginning of what would become the deadliest eruption in United States' history. Fifty-seven people lost their lives. NASA notes that this was not the mountain's largest or longest-lasting eruption, but the first to occur (in the continental U.S.) during the era of modern scientific observation.
NASA reports that on May 18th, the eruption peaked as an earthquake caused the collapse of the mountain's northern flank. The collapse resulted in the most massive landslide in recorded history, burying the North Fork Toutle River for 23 kilometers and up to 180 meters deep in some places. The subsequent explosion blasted rocks, gas, and steam over 600 square kilometers. Additionally, as reported by NASA, the explosion decimated more than 4 billion board-feet of timber. The eruption melted remaining snow and ice, releasing devastating lahars. In just four minutes, the blast cloud reached 30 kilometers in altitude. USGS reports that the ash cloud reached the central U.S. by May 19th, and some traveled around the globe within two weeks.
The recovery of the surrounding landscape would be long and challenging. Fortunately, The Landsat Program from NASA and USGS has been using satellites to acquire images of the volcano before this significant eruption event. This allows scientists to know what the area looked like before the event and track recovery since 1980. NASA considers this an "unprecedented opportunity to witness the intricate steps through which life reclaims a devastated landscape."
According to NASA, the first noticeable recovery occurred in the late 1980s, in the northwestern quadrant farthest from the volcano. Landsat images show green vegetation returning to the region and getting closer to the mountain by the late 1990s. The most recent article from NASA regarding the eruption states that changes are slow and are now appearing less dramatic in annual images as recovery continues. Steve Self, professor at the University of California, Berkeley, stated, "I think these long-time series will be useful for decades to come, possibly out to a century after the eruption, as change is very slow."