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Beneath crumbling walls: how rock glaciers took over the southern rockies

Gabe Allen — Wed, 18 Jun 2025 22:24:17 +0000

Beneath crumbling walls: how rock glaciers took over the southern rockies Gabe Allen Wed, 06/18/2025 - 16:24

Gabe Allen

20,000 years ago, during the last glacial maximum, hulking formations of flowing ice stretched across the Southern Rocky Mountains in present-day Colorado. Most of those glaciers melted away by around 13,000 years ago, but that doesn’t mean Colorado’s glaciers are gone. They’ve just gone underground. Today, the state is home to thousands of rock glaciers — icy formations protected by layers of debris.

“Anybody who climbs the fourteeners of Colorado, whether they know it or not, is climbing across a rock glacier here or there,” INSTAAR fellow and distinguished professor of geologic sciences Robert Anderson explained.

Last month, Robert Anderson and Suzanne Anderson, also an INSTAAR fellow and professor of geology, published a new study documenting how rock glaciers form. According to their analysis, the main ingredients are snow and a protective layer of rocky debris, usually provided by a tall, erosion-prone cliff overhead. Importantly, there can’t be too much ice and snow.

“The speed at which the ice moves away from the base of the cliff is governed by how thick the ice is. The thicker it is, the faster it goes,” Robert Anderson explained. “It can’t be too thick. So, avalanche run-outs are sort of the magic zone for the top of a rock glacier.”

A gap in geologic history

The Andersons’ new model of rock glacier formation led to a second insight — one about the past. According to the study, the rock glaciers we see in the Colorado Rockies today likely formed hundreds, or even thousands, of years after the big glaciers disappeared. That’s because rock glaciers actually require more temperate conditions to establish themselves.

“We argue that you lose almost all of the ice out of the alpine valleys. Then, only later, it comes back in a rock glacier mode,” Robert Anderson said.

The model is also backed by physical evidence collected by the Andersons, their students and a number of other researchers over the past three decades. To determine the age of rock glaciers, these researchers tested samples from boulders on the surface of the glaciers for a rare isotope of the element beryllium. The results indicate how long the boulder has been there, and thus how long ago the glacier formed. According to these analyses, Colorado’s rock glaciers arose around 10,000 to 12,000 years ago, which places them at least a thousand years after deglaciation.

Robert Anderson says that understanding how rock glaciers formed gives us a more clear understanding of their role in the landscape today. It might help us conserve them too.

“It’s an important part of climate history,” he said.

Rock glaciers and water

Suzanne Anderson gathers water samples from a mountain creek near the Mount Sopris rock glacier. Photo by Robert Anderson.

Today, rock glaciers are ubiquitous in Colorado’s alpine landscapes, but the role they play in mountain ecosystems is still poorly understood. According to Suzanne Anderson, the key to further understanding may lie in the unique water rock glaciers provide.

“It’s different from other water sources in the landscape for two reasons,” Suzanne Anderson explained. “It’s cold, even late in the summer, because it's coming directly from ice melt, and its chemistry is different — it’s a little more nutrient-rich.”

Some research has already suggested that certain cold-adapted insects may rely on this meltwater for survival. The Andersons and their students have also found elevated levels of nitrogen, an important nutrient for both plants and animals, in rock glacier meltwater.

One of Suzanne Anderson’s students, M.S. student Maya McDonough, is furthering these investigations. This summer, McDonogh will sample meltwater from a rock glacier near Imogene Pass, between Telluride and Ouray, Colorado and analyze its chemistry.

“We’re testing the water chemistry to see what ions are in rock glacier discharge, because those nutrients might be really important to certain high-altitude habitats,” McDonough said. “I’ll test as many samples as I possibly can.”

Rock glaciers everywhere — at least in the Colorado Rockies. New research from Robert and Suzanne Anderson investigates how they formed, and what benefits they might provide for alpine ecosystems.

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The headwall of Mount Sopris looms above a large rock glacier in the basin below. Photo by Robert Anderson.

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The headwall of Mount Sopris looms above a large rock glacier in the basin below. Photo by Robert Anderson.

Juliana Ruef is awarded the Sarah Crump Graduate Fellowship

Gabe Allen — Fri, 04 Apr 2025 12:00:00 +0000

Juliana Ruef is awarded the Sarah Crump Graduate Fellowship Gabe Allen Fri, 04/04/2025 - 06:00

Gabe Allen

INSTAAR is excited to announce that incoming PhD student Juliana Ruef is the 2025 recipient of the Sarah Crump Graduate Fellowship. Ruef will use the award for snow science research on the Juneau Icefield in Alaska this summer.

The Sarah Crump Graduate Fellowship was designed by Sarah Crump, a beloved INSTAAR alum who passed away in November 2022. Each year, the fellowship provides funding for one graduate student studying earth or environmental science in high-latitude or high-altitude regions.

Juliana Ruef, the recipient of the 2025 Sarah Crump Graduate Fellowship, poses for a portrait.

Though Ruef hasn’t started her PhD yet, she is already at INSTAAR working on a MS degree with INSTAAR faculty Robert Anderson and Bradley Markle. Her PhD research will focus on the evolution and dynamics of rock glaciers and firn—granular ice that forms between snow and glaciers.

Ruef will use the fellowship funds to pay herself and an undergraduate research assistant to gather data for firn evolution research project this summer. The funding will also help pay for travel to and from the Juneau Icefield as well as essential supplies for data collection in the field.

Ruef’s advisors cited her focus on community-building and her high research standards in a recommendation letter.

“We can think of few students who so closely embody Sarah’s passion for scientific understanding of the alpine world as well as her commitment to making science a better community,” Markle and Anderson wrote.

You can visit this link to learn more about the Sarah Crump Graduate Fellowship or donate to the fund.

Juliana Ruef processes a freshly-drilled "firn core" on the Juneau Icefield in 2024.

If you have questions about this story, or would like to reach out to INSTAAR for further comment, you can contact INSTAAR Communications Specialist Gabe Allen at gabriel.allen@colorado.edu.

Ruef is the third recipient of the summer fellowship created in honor of a now-passed INSTAAR alum. She will use the funding for snow science research on the Juneau Ice Field in Alaska this summer.

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Juliana Ruef on the Juneau Ice Field in Alaska.

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Kirk Bryan Award goes to a team of INSTAARs, colleagues

Anonymous — Thu, 19 Oct 2023 21:34:00 +0000

Kirk Bryan Award goes to a team of INSTAARs, colleagues Anonymous (not verified) Thu, 10/19/2023 - 15:34

Shelly Sommer

A team of researchers that included several INSTAAR scientists received the prestigious Kirk Bryan Award from the Quaternary Geology & Geomorphology Division of the Geological Society of America (GSA). The prestigious award honors the authors of a recent paper that advances the science of geomorphology.

Led by former INSTAAR PhD student Simon Pendleton, now an Assistant Professor of Practice at Plymouth State University, the team of researchers included INSTAARs Gifford Miller, Scott Lehman, Sarah Crump, and Robert S. Anderson and colleagues Nathaniel Lifton from Purdue University and John Southon from the University of California, Irvine.

Their paper in Nature Communications, “Rapidly receding Arctic Canada glaciers revealing landscapes continuously ice-covered for more than 40,000 years,” was published in 2019. The study looked at the ages of ancient plants preserved by now-receding ice caps in Arctic Canada. It found that the summer warmth of the past century now exceeds any century in within the past 115,000 years. In an acceptance speech at the GSA annual meeting, Pendleton described a long and collaborative process that led to the paper’s publication, involving, “the chance collection of preserved plants nearly 60 years ago, some not insignificant improvements in radiocarbon dating, the invention of an entirely new surface dating technique (cosmogenic exposure dating), and the perseverance of individuals in the pursuit of understanding these landscapes and the climate secrets they hold.” The researchers spent hours walking ice margins on Baffin Island and processed hundreds of preserved plants in labs to date the plants and place them in a context stretching for thousands of years. He added, “In many ways, this paper encapsulates the theme of the Kirk Bryan award: the innovations made by others over past decades enabled our team to continue to advance the field and our understanding of these glacier-climate systems.”

“It was only recently that I fully appreciated the irony of this particular project,” said Pendleton. “The irony that the warming of the climate—the very thing we are attempting to quantify and characterize—is revealing to us, through ice recession, the data we need to do it. These newly exposed materials are ephemeral, and once they are gone, the record is lost forever.”

The award comes with a monetary prize, which the authors will donate to the Sarah Crump Graduate Fellowship. Sarah Crump was an author on the paper who contributed significantly to the field and lab portions of the study. She passed away in 2022 after a battle with cancer, leaving a legacy of outstanding paleoclimate science paired with a strong commitment to inclusion and community building.

Previous Kirk Bryan Award winners from the University of Colorado Boulder include John Andrews in 1973 and Peter Birkeland in 1988.

Simon Pendleton and Giff Miller collect ancient plant remains melted out of the edge of an ice cap on Baffin Island. Photo by Matt Kennedy, Earth Vision Trust.

Giff Miller holds a clump of ancient moss, recently melted out of the edge of an ice cap on Baffin Island. Photo by Matthew Kennedy, Earth Vision Trust.

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Two ��Ҵ�ý�ƽ�� profs elected to National Academy of Sciences (Colorado Arts and Sciences Magazine)

Anonymous — Fri, 07 May 2021 06:00:00 +0000

Two ��Ҵ�ý�ƽ�� profs elected to National Academy of Sciences (Colorado Arts and Sciences Magazine) Anonymous (not verified) Fri, 05/07/2021 - 00:00

Geologist (and INSTAAR) Robert S. Anderson and astrophysicist Fran Bagenal recognized for ‘distinguished and continuing achievements in original research’.

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Anderson R

Beneath crumbling walls: how rock glaciers took over the southern rockies

A gap in geologic history

Rock glaciers and water

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Juliana Ruef is awarded the Sarah Crump Graduate Fellowship

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Kirk Bryan Award goes to a team of INSTAARs, colleagues

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Two ���Ҵ�ý�ƽ������ profs elected to National Academy of Sciences (Colorado Arts and Sciences Magazine)

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Two ��Ҵ�ý�ƽ�� profs elected to National Academy of Sciences (Colorado Arts and Sciences Magazine)