On May 18, 1980, at 8:32 a.m. Pacific Daylight Time, a magnitude 5.1 earthquake shook Mount St. Helens. The bulge and surrounding area slid away in a gigantic rockslide and debris avalanche, releasing pressure, and triggering a major pumice and ash eruption of the volcano. Thirteen-hundred feet (400 meters) of the peak collapsed or blew outwards. As a result, 24 square miles (62 square kilometers) of valley was filled by a debris avalanche, 250 square miles (650 square kilometers) of recreation, timber, and private lands were damaged by a lateral blast, and an estimated 200 million cubic yards (150 million cubic meters) of material was deposited directly by lahars (volcanic mudflows) into the river channels. Fifty-seven people were killed or are still missing.
Credit: USGS, Austin Post, Public Domain
When Mount St. Helens erupted in 1980, lava incinerated anything living for miles around. As an experiment, scientists later dropped gophers onto parts of the scorched mountain for only 24 hours. The benefits from that single day were undeniable—and still visible 40 years later.
Once the blistering blast of ash and debris cooled, scientists theorized that, by digging up beneficial bacteria and fungi, gophers might be able to help regenerate lost plant and animal life on the mountain. Two years after the eruption, they tested this theory.
"They're often considered pests, but we thought they would take old soil, move it to the surface, and that would be where recovery would occur," said UC Riverside microbiologist Michael Allen.
They were right. But the scientists did not expect the benefits of this experiment would still be visible in the soil today, in 2024. A paper published in the journal Frontiers in Microbiomes details an enduring change in the communities of fungi and bacteria where gophers had been, versus nearby land where they were never introduced.
"In the 1980s, we were just testing the short-term reaction," said Allen. "Who would have predicted you could toss a gopher in for a day and see a residual effect 40 years later?"
In 1983, Allen and Utah State University's James McMahon helicoptered to an area where the lava had turned the land into collapsing slabs of porous pumice. At that time, there were only about a dozen plants that had learned to live on these slabs. A few seeds had been dropped by birds, but the resulting seedlings struggled.
After scientists dropped a few local gophers on two pumice plots for a day, the land exploded again with new life. Six years post-experiment, there were 40,000 plants thriving on the gopher plots. The untouched land remained mostly barren.
An unhappy gopher and plant near the gopher enclosure fence, 1982.
Credit: Mike Allen/UCR
All this was possible because of what isn't always visible to the naked eye. Mycorrhizal fungi penetrate into plant root cells to exchange nutrients and resources. They can help protect plants from pathogens in the soil, and critically, by providing nutrients in barren places, they help plants establish themselves and survive.
"With the exception of a few weeds, there is no way most plant roots are efficient enough to get all the nutrients and water they need by themselves. The fungi transport these things to the plant and get carbon they need for their own growth in exchange," Allen said.
A second aspect of this study further underscores how critical these microbes are to the regrowth of plant life after a natural disaster. On one side of the mountain was an old-growth forest. Ash from the volcano blanketed the trees, trapping solar radiation and causing needles on the pine, spruce, and Douglas firs to overheat and fall off. Scientists feared the loss of the needles would cause the forest to collapse.
That is not what happened. "These trees have their own mycorrhizal fungi that picked up nutrients from the dropped needles and helped fuel rapid tree regrowth," said UCR environmental microbiologist and paper co-author Emma Aronson. "The trees came back almost immediately in some places. It didn't all die like everyone thought."
On the other side of the mountain, the scientists visited a forest that had been clearcut prior to the eruption. Logging had removed all the trees for acres, so naturally there were no dropped needles to feed soil fungi.
"There still isn't much of anything growing in the clearcut area," Aronson said. "It was shocking looking at the old growth forest soil and comparing it to the dead area."
These results underscore how much there is to learn about rescuing distressed ecosystems, said lead study author and University of Connecticut mycologist Mia Maltz, who was a postdoctoral scholar in Aronson's lab at UCR when the study began.
"We cannot ignore the interdependence of all things in nature, especially the things we cannot see like microbes and fungi," Maltz said.
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