Downed Tree Samples Aid Research Of Epic Avalanche Cycle
Mike Cooperstein and Jason Konigsberg maneuvered a 6-foot long cross-cut saw with menacing teeth into position Tuesday on a hulking spruce trunk that was ripped out of the ground by an avalanche in March 2019.
"It makes a ringing sound when you get a groove going," said Konigsberg, who had prior experience as a sawyer while working on U.S. Forest Service trail crews.
Indeed, the two-person cross-cut saw did emit a ring as they sliced into the dried wood. Before long they completed the cut through the 42-centimeter diameter trunk, then immediately started another just inches away from the first. Their work produced a disk or cookie of wood that exposes the tree rings.
The men were part of a four-person crew from the Colorado Avalanche Information Center along with Brian Lazar and Brandon Levy, and they harvested 12 cookies recently 2 miles up the East Snowmass Creek Trail outside of Snowmass Village.
A massive, D5 avalanche started at Garrett Peak and continued roughly 2 miles of the ridgeline toward Willow Pass at the end of a historically significant avalanche cycle in March 2019. The slide rolled down about 2,200 vertical feet. D5 is the highest on the destruction scale. It is a landscape-altering event.
The Garrett Peak/East Snowmass Creek slide was one of three D5 slides known to have occurred during the cycle, according to Lazar, CAIC's deputy director and a Carbondale resident. Another of the most destructive slides occurred in Conundrum Valley southwest of Aspen.
CAIC recorded about 1,000 avalanches in the Colorado mountains during the cycle. Lazar previously said in presentations that the total number could easily be five times greater.
"To put it into perspective, there's nobody alive today who has been in a cycle quite like this in Colorado," Lazar said. "These are less than once in a lifetime cycles. They're quite rare."
And, thus, the cycle makes for a goldmine of research opportunities.
"It provides a rare opportunity to get insights into a few things. One is what is the set-up necessary to produce these kind of events?" Lazar said. "We can try to get some insights into the frequency or return intervals of these events."
Other research will be in avalanche flow dynamics and impact pressures.
The cookies cut from the tree trunks are the key to that research. Dendrochronologists with the U.S. Forest Service and U.S. Geological Survey will extract clues about Colorado's climate from the tree ring growth.
They will also look for the presence of "reaction wood," abnormal growth on the lower side of trees positioned on an incline. It can signal impacts from major events like avalanches or small incidents like a boulder crashing down. The presence of reaction wood can tell a dendrochronologist if the trees that were felled in the 2019 avalanche cycle suffered major, prior impacts and how long ago.
CAIC has harvested 730 tree disks or cookies so far over the past two summers for research by its partners. They target Engelmann Spruce and other conifers, which grow slow and therefore provide a longer picture than faster growing aspen trees. By providing lots of samples, researchers can look for longer-term trends in climate and avalanche activity.
In the field, the CAIC workers measured the length of the tree trunks and diameter at human breast level. They noted factors such as a "broken butt" and "broken tip" and whether the subject tree was in place where the force of the avalanche knocked it down or if it was swept away.
The information is entered into an app on their smart phones. Once they returned to cellular service, it automatically downloaded into the CAIC database.
After the cookies are carved from the trees, the workers use a Sharpie to label the location. They will be placed in storage until they can be delivered to the Forest Service's Fraser Experimental Forest in Fraser, Colorado. There, the cookies will be sanded, labeled with metal tags and mounted on material before they are shipped to a U.S. Geological Survey facility in Bozeman, Montana, where they will be analyzed.
Lazar and company didn't have to look hard for appropriate samples on East Snowmass Creek. The massive slide felled thousands of conifer and aspen trees. The trunks lie in a mixed jumble on the valley floor. The force of the avalanche was so great that snow and debris swept up the opposite valley wall and knocked over hundreds of additional trees.
Once cleared of tree cover, the valley floor came to life with fireweed, arnica, paintbrush and multiple other varieties of wildflowers. In the slide paths, thin aspens that bent rather than broke when the slide thundered down now dot the landscape. A few bedraggled conifers remain standing where the slide struck.
"They got hammered," Lazar said of the standing trees. "They got branches ripped out 50 feet high."
Small core samples will be taken from the standing trees for analysis.
Lazar said that at first glance, it appeared some of the trees in the Garrett Peak slide were more than 100 years old and possibly up to 150 years, but he cautioned that was a guess.
"Dendrochronology is really not our area of expertise," he said. "That's why we bring in folks from the Forest Service and U.S.G.S. who are a lot more experienced doing this kind of stuff."
Avalanche center crews previously harvested cookies from areas that were easier to access and where chainsaws could be used. The avalanche carnage in East Snowmass Creek is within the Maroon Bells-Snowmass Wilderness, so handsaws must be used. Mechanized and motorized uses are prohibited in designated wilderness except for medical emergencies.
Cookies were also cut in the Aspen area from the massive slide in Conundrum. In East Snowmass Creek, CAIC crews also harvested cookies from a previous trip and would likely return for another two to create a total of 20 samples, according to Lazar.
His goal is to also get up Lincoln Creek drainage east of Aspen to collect samples from multiple slide paths.
CAIC will share results of the studies in coming years.
"We couldn't sample every avalanche path because so many ran," Lazar said. "It's been kind of triaging which ones we can do, looking at some of the bigger avalanches events, looking at ones that impacted highways. We have a list of avalanche paths we'd like to get to. Garrett was certainly on the list not because of an impact to a roadway but because of the sheer size of the avalanche in East Snowmass Creek."
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