Fossil finds in Snowmass lead to earthquake theory
Earthquakes might have led to the death of the more than 30 mastodons whose remains were recovered from Ziegler Reservoir near Snowmass Village during an excavation that wrapped up last summer.Scientists are testing the quake hypothesis even as more Ice Age species emerge from muck that was carted from the reservoir to the Denver Museum of Nature & Science. Thirty-four species have now been documented, and Dr. Kirk Johnson, leader of the excavation team and vice president of the museum’s Research and Collections Division, expects the list to grow, even as Ziegler Reservoir refills with water.”I think we’re going to keep adding species to the list for many months to come,” said Johnson in a telephone interview Thursday from Denver. Several tons of dirt were hauled back to Denver when the dig wrapped up July 1; crews are sifting carefully through it, finding evidence of various animals, including lizards, bats, trout and rodents – most recently a lemming, Johnson reported.While scientists continue to piece together the history of Ziegler Reservoir, an artist has captured perhaps the most telling story of the lake’s evolution, starting with its formation some 130,000 years ago when a glacier spilled out of the Snowmass Creek Valley, to its present-day appearance.Shortly after the first discoveries at Ziegler, a little more than a year ago, Johnson summoned Minnesota muralist Jan Vriesen to paint the scene. Vriesen returned again in June.”It’s a tricky thing for an artist to do – you’re asking them to paint something they can’t see,” Johnson said. “A picture really is worth more than a thousand words when you talk about prehistoric landscapes because no one can see these things.” The series of five paintings includes a representation of what the lake would have looked like about 120,000 years ago, when the area was dominated by mastodons, giant ground sloths and bison; and one depicting the scene 60,000 to 45,000 years ago, when mammoths, camels and deer were prominent. A painting of the drained reservoir when the fossils first were found, and one with the lake restored, complete the series.Vriesen’s paintings share the same vantage point – from the north side of the lake looking south, with what is now the Snowmass ski area visible to the left, and the Snowmass Creek Valley and Mount Daly visible to the right. The landscape that exists today was in place when mastodons walked the earth, Johnson said. Fossils and pollen grains recovered from the reservoir dictate the plants and animals that appear in the 38-by-57-inch acrylic paintings.”The place hasn’t changed dramatically in topography for the last 150,000 years,” Johnson said. “We were able, very quickly, to come to very plausible scenarios.””This is very close to what it looked like,” he said of the paintings, noting that the taller vegetation in the depiction of the lake 120,000 years ago, versus what is seen in the more recent scene, of life 60,000 to 45,000 years ago, when the lake was filling in and the area was less lush.Scientists have determined, from the evidence they’ve collected, that the climate was warmer than it is today when mastodons roamed the area, but colder when mammoths appeared, Johnson explained.But it was a modern-day tip that led to the earthquake theory. It was during the enlargement of Ziegler Reservoir, a project that included construction of a new, earthen dam, that the Ice Age fossils were discovered. Engineers saw the need to remove silt from the ancient lake bed before building a dam because documented seismic activity would make silt a potentially unstable base.”The silt was in the lake when the mastodons were there, too,” said Johnson, leading to a theory first proffered by mastodon expert Dr. Dan Fisher from the University of Michigan.Fisher, among the first wave of scientists summoned to Ziegler in 2010, is helping test the hypothesis that mastodons were trapped in the lake sediment by an earthquake or series of quakes that would have, in essence, turned the silt to quicksand, Johnson explained. Saturated sediment will turn to liquid when it’s shaken, he said.”It happens very rapidly – it’s one of the big hazards in earthquake areas,” he said.If a group of animals was stuck suddenly, they would have died over time and begun to decay where they stood. A subsequent earthquake could have caused the debris flow that scientists believe scattered the bones.”The bones were beautifully preserved, but they weren’t attached to each other,” Johnson said. “Pretty elaborate theory … it’s one of the few ways we have to explain the pattern we see.”The age rings in the recovered mastodon tusks allows Fisher to determine if the animals died during the same season of the year. That appears to be the case for a number of the adult animals, helping further the theory, Johnson said. On another front, two DNA labs are attempting to extract the genetic material from the fossils and have recovered some short strands of DNA.”We’ve got it, but we can’t do anything with it,” Johnson said. With longer strands, scientists could compare the fossils to mastodon finds elsewhere. DNA also is the material scientists use to clone animals.In all, some 40 scientists throughout the country and beyond continue to study the Ziegler story.Johnson’s focus at the museum remains the so-called Snowmastodon Project. In Denver, the museum staff continues to examine and log the thousands of bones retrieved from Ziegler Reservoir, including huge skulls and other fossils that were encased in plaster at the site for transport to the Front Range. About half of the 76 plaster jackets have been opened, yielding new discoveries, he said.Often, protruding bones and the dirt around them were quickly jacketed without any real examination at the reservoir early last summer.”In many cases, we’re seeing these for the first time,” Johnson said.Work on a book is also under way – Johnson expects “Digging Snowmastodon” to be published in the spring. And, when he’s not in Denver, Johnson’s talking about the Ziegler finds at speaking engagements.”It’s a big deal, and it’s got a lot of national interest,” he said.Meanwhile, Ziegler Reservoir, no longer in the media spotlight, is slowly refilling with water.”It’s been filling for about 10 days. We’re making good progress,” said Kit Hamby, director of Snowmass Water and Sanitation. The lake, surrounded by private property, should be refilled by January, he said.The museum dig focused on the area where a new dam was built to ensure that no fossils were destroyed. Whatever lurks in the rest of the reservoir sediment will remain protected, as it has for hundreds of thousands of years, according to Johnson.firstname.lastname@example.org
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