Live Science, Planet Earth, Mount St. Helens Eruption: Facts & Information, https://www.livescience.com/27553-mount-st-helens-eruption.html
NASA, Earth Observatory, Devastation and Recovery at Mount St. Helens, Lindsey, Rebecca, https://earthobservatory.nasa.gov/Features/WorldOfChange/sthelens.php
Oregon State University, Volcano World, What Were the Effects on People When Mount St. Helens Erupted, http://volcano.oregonstate.edu/what-were-effects-people-when-mt-st-helens-erupted
The Atlantic, The Eruption of Mount St. Helens in 1980, https://www.theatlantic.com/photo/2015/05/the-eruption-of-mount-st-helens-in-1980/393557/
USA Today, ‘I’m going to stay right here.’ Lives Lost in Mount St. Helens Eruption, https://www.usatoday.com/story/news/nation-now/2015/05/17/mount-st-helens-people-stayed/27311467/
USGS, Impact and Aftermath, https://pubs.usgs.gov/gip/msh/impact.html
The USA Today article has insightful stories of some of the people that died during the eruption, such as Harry Truman who lived on Spirit Lake and refused to leave. Mr. Truman and his lodge was buried in the avalanche. But the article that gave the best information on the human impact was the last article that is listed from the USGS website. It puts into perspective the massiveness of the devastation that occurred from the landslide, lateral blast, and the lahars. Spirit Lake, where Harry Truman lived, and all of the buildings in the area were completely buried from the debris avalanche and lateral blast. There was extensive damage to land and civil works, more than 200 homes and cabins were destroyed and many more were damaged leaving many families homeless.
Thousands of acres of prime forest, totaling more than 4 billion board feet of salable timber, were destroyed mostly from being blown down by the lateral blast. During the timber-salvage operations, 600 truckloads of timber were transported from the area each day. Fifteen miles of railways, 57 bridges and 185 miles of highways were extensively damaged or destroyed along with recreational sites and trails.
Nearly seven thousand big game animals such as deer, elk and bear died during the eruption along with all the birds and small animals in the area. Fish hatcheries were destroyed killing approximately twelve million Chinook and Coho salmon fingerlings and 40,000 young salmon.
Fifty-seven people died, mostly from asphyxiation from inhaling the hot ash. Loggers, campers, fisherman, and families on outings were included in those numbers as well as the USGS Volcanologist David Johnston. Over three billion tons of ash was spread across the surrounding areas, covering streets, buildings, interfering with communication systems, airports, and spreading across 11 states.
A couple of sites that I looked at had some conflicting information with numbers, but I feel confident that the numbers and information coming from the USGS are the most accurate especially since the Cascades Volcano Observatory is part of the USGS Volcano Hazards Program. As I looked at many different resources, it seems I always gravitate back to the USGS website to see if the information is the same. They also have great photos documenting the unbelievable devastation.