What's Happening Below Hallett Peak in Chaos Canyon and Lake Haiyaha

Looking up at the south slope of Hallett Peak from Lake Haiyaha, rock debris is seen sliding downhill into Chaos Canyon below.

USGS Photo/M. Morris

Chaos Canyon and Areas West of Lake Haiyaha Have Reopened

Chaos Canyon and areas west of Lake Haiyaha have reopened to all users however, talus slopes and rocks in Chaos Canyon are unstable and may continue to slide much like any other similarly situated exposures in Rocky Mountain National Park. This is a popular area for bouldering.

Rocky Mountain National Park is a wilderness park and there are inherent risks when recreating in wild spaces. Chaos Canyon has been closed since June 28, 2022, due to a significant landslide event that occurred on the south slope of Hallett Peak.

 

Figure 1 from Allstadt and others (2024)

What Led to the Chaos Canyon Landslide?

Following the landslide event, Rocky Mountain National Park staff have been collaborating with the NPS Geological Resource Division and United States Geological Survey (USGS) to investigate the potential causes of this slide and to learn more.

An article focused on this event and what has been learned is titled “The 2022 Chaos Canyon Landslide in Colorado: Insights Revealed By Seismic Analysis, Field Investigations, and Remote Sensing” by Allstadt, K.E., Coe, J.A., Collins, E.A. et al. Landslides 21, 309-325 (2024). This article is available online at https://doi.org/10.1007/s10346-023-02179-4.

Based on initial observations, taken June through August 2022, the Hallett Peak event appeared to be a landslide event. Researchers have found that beginning in the early to mid-2000s deformation of the mountain side on the south slope of Hallett Peak had already occurred and began to accelerate in 2018. This likely led to the slope failure in 2022.

 

Figure 5 from Allstadt and others (2023)

The volume of the slide was estimated to be 2.7 million cubic yards (2.1 cubic meters) of material which reached speeds of up to 11mph (5 meters/second) and slid on a surface ~260 feet (80 meters) deep.

Based on a few lines of evidence found in the debris following the event, researchers hypothesize the slide was prompted by increases in long term air temperatures that thawed permafrost and ice increasing pore pressures. Park staff will continue to assess this area within Chaos Canyon.

 

Why did the Color of Lake Haiyaha Change?

The grinding action of the debris slide in Chaos Canyon transported a lot of silt and clay downhill quickly and into Lake Haiyaha. This process is similar to what happens with glaciers over long periods of time.

Glaciers work to grind and pulverize rocks along valley floors and walls. These processes produce a fine-grained powder of silt and clay called "glacial flour." In the case of Lake Haiyaha, however, the grinding of rock was not from the slow work of glaciers. It occurred quickly during the debris slide resulting in a pulse of "rock flour" transported to the lake. Since the particles are so fine, they are slow to sink to the bottom, remaining suspended in the water column instead.

When sunlight hits the water, these particles absorb the shortest wavelengths, the purples and indigos. Meanwhile, the water absorbs the longer wavelength reds, oranges, and yellows. That leaves mainly blues and greens to get scattered back to our eyes.

This is what makes Lake Haiyaha appear a milky sea-green color.

How Long will Lake Haiyaha be this Unique Color?

It is unknown how long Lake Haiyaha will appear to look this milky sea-green color. Many different factors play a role in this process, such as:

• Whether the debris slide activity in Chaos Canyon continues to transport more rock flour into Lake Haiyaha
• How long it takes for the fine silt and clay particles to sink to the bottom of Lake Haiyaha (this will depend on the particle density and shape, wind turbulence, lake depth, and mixing of the lake's water).

 

NPS

Top Image: Lake Haiyaha as seen before the Hallett Peak debris slide

 

NPS

Bottom Image: Lake Haiyaha as seen after the Chaos Canyon debris slide.