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Acres of destruction left by Colorado’s historic avalanche season are also delivering climate change evidence

Researchers think secrets hidden in the rings of millions of felled trees may reveal the relationship between climate and avalanche cycles

Two student researchers were sent with chainsaws to a debris field above Silverton, Colorado, to collect tree-ring specimens for dendrochronologists looking for data about the avalanche cycle in Colorado. (Nina Riggio, Special to The Colorado Sun)
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A stunning avalanche season saw thousands of slides snap mature tree trunks like twigs, wipe historic buildings off the map and radically alter Colorado’s mountain landscape.

But the big slides that splintered conifer forests and felled massive aspen groves also delivered an important new scientific resource to the Colorado Avalanche Information Center and U.S. Forest Service: downed trees.

Now a team of researchers is working through the wreckage, collecting cross sections from the fallen trees that they say will help them learn more about the relationship of climate to avalanche cycles.

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It’s difficult and time consuming to take samples from the living forest — researchers usually extract a thin cylinder from a tree trunk. Now, all researchers need is two cuts with a chainsaw to remove a complete disc. With a tremendous sample size available, they think the tree-ring specimens will provide powerful data as they develop a plan for a future that holds potential for more extreme weather, and more risk of avalanche, due to climate change.

“We just decided that we needed to understand this a lot better, so that we understood where this avalanche cycle was in the trajectory of history,” avalanche center director Ethan Greene said. “That was really going to help us, both scientifically because it’s a pretty interesting event, but also in terms of planning.”

Coleman Kane, a recent graduate of Fort Lewis College in Durango, holds a dendrochronology specimen collected on June 2, 2019, from avalanche debris outside Silverton. Researchers are using chainsaws to collect as many samples as they can from avalanche debris statewide, hoping the tree rings will help them better understand the relationship between climate and avalanche cycles since before history was recorded in Colorado. (Nina Riggio, Special to The Colorado Sun)

Colorado hopes to use the research to improve building codes to keep power lines and homes out of harm’s way. The huge sample size also may help other scientists who can examine tree rings to learn about Colorado’s climate long before white settlers began recording information.

While the devastating season claimed lives, roads and property across the state, Greene sees potential in the chaos. Researchers typically must scour the globe to find such an anomalous season.

“We sort of know that those events are possible, but we haven’t really seen them and we really don’t know how likely they are,” Greene said.

Kelly Elder, a research hydrologist for the U.S. Forest Service, helps collects tree-ring specimens in partnership with the Colorado Avalanche Information Center. Researchers wielding chainsaws are collecting as many samples as they can from as many avalanche paths as they can reach before the snow flies again. (Nina Riggio, Special to The Colorado Sun)

This season presented an opportunity that researchers didn’t want to lose, said Kelly Elder, a research hydrologist for the U.S. Forest Service who in early June was collecting samples from trees near Silverton. “A bunch of us came together and realized this is a real opportunity and we should jump on it.”

By dating trees in avalanche paths, researchers can measure the length of time between avalanche cycles. This type of work is known as dendroecology — the study of tree-ring patterns and the ecological factors that create them, which can include climate. 

Extreme events can kill a tree. Elder said some of the trees downed this cycle are at least 250 years old, meaning the areas where they grew hadn’t seen a big avalanche in more than two centuries.

Even if the tree wasn’t killed by an avalanche, Elder says the force of a slide can cause it to develop a distinct ring, similar to scar tissue, that scientists can use to plot the time gap between avalanches. 

So far, the study is confirming what was suspected: this avalanche season was unprecedented, at least in Colorado’s recorded history.

“We don’t know how rare it is because nobody has ever seen anything like it,” Greene said, referencing the historic record that began with mining settlements in the 1800s. “It’s outside of that record. And there are some places where it’s far outside of that.”

In a typical big avalanche season, Greene said 30% to 60% of an area might slide. This year, 80% of many valleys slid, and at even higher percentages in some regions. “Every piece of avalanche terrain in a drainage avalanched — which is something that, you know… I’ve never seen anything like that.”

Tree-ring specimens, collected from avalanche debris are stacked before being taken for analysis by dendrochronologists trying to plot the relationship between climate and avalanche cycles in Colorado. The work is intended to inform planning for such things as building codes and zoning in Colorado’s high country as the climate changes. (Nina Riggio, Special to The Colorado Sun)

Peter Brown, founder of the nonprofit Rocky Mountain Tree-Ring Research, said climate research is one of the main applications of dendrochronology, the broader scientific umbrella under which dendroecology falls. By studying the record of Colorado’s climate stored in tree rings (in cold climates, like Colorado, trees only grow in the summer and grow more in warmer, wetter years) researchers can get a long view of weather history that provides a backdrop for new data as the state begins to see the effects of climate change. 

“A big use of dendrochronology in recent years has been to place global warming,” Brown said. “What’s natural climate variability and what’s unprecedented in the last few centuries?” 

Elder and Greene hope the study will help plan for extreme weather events in Colorado. While the effect of climate on avalanches is a seldom-studied subject, extreme weather is one of the big threats the Intergovernmental Panel on Climate Change warned of in its alarming 1.5-degree report, which concluded the Earth is on track to warm by 1.5 degrees Celsius between 2030 and 2052.

“We’re living in a time right now of increased variability in weather systems,” Elder said. “A lot of the models that we use for climate-related phenomenon are essentially useless because they’re based on a mathematical assumption that the variability is consistent.”

It’s hard to say whether any specific avalanche was caused by climate change. But Greene says that more than any slide path in particular, he fears that avalanche cycles will be affected, which could mean more unprecedented seasons. 

“It’s certainly something that we need to consider and be ready for,” Greene said.

Elder and his team will be out cutting samples until it starts to snow again, and might even continue the project next summer. Both he and Greene hope the new information can help preserve buildings, infrastructure and lives.

“We want to try to make sure that we make the most of this so that as people continue to work, play, build houses, build roads, travel roads in Colorado, we have the best information for them to make good decisions,” Greene said.


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