Introduction

There are more than 135 permanent snow or ice bodies mapped in Colorado, but only 7 of these are larger than 0.1 km2. Colorado has 14 named glaciers - all in the Front Range, most significantly in Rocky Mountain National Park. The total area of all the mapped snow and ice bodies in Colorado is about 4.8 km2. The seven regions of Colorado glaciers are examined further below. Note: all statistics here are based on USGS 1:24,000 scale topographic quadrangle maps which are based on mapping photography ranging from 1952 to 1985. The MODIS image displayed on the right illustrates the areas of higher elevation in Colorado in white (late spring snowpack), while the blue areas are glaciers (these blue features have been added to the MODIS image). The glaciated areas of Colorado include all the white areas and locally significant portions of the green forested areas. Most glaciers and snowfields in Colorado occur in east- to north-facing cirques at high elevations near the ridge crests. These locations favor snow accumulation from avalanches and windblown snow in the winter and are well-protected in shade from summer sun. It is highly unlikely that any of Colorado's glaciers could exist today without the benefit of these local topographic effects. Many of the features appear to feed rock glaciers, and the area of debris-covered ice in the state may be significantly larger than that of exposed clean ice.

MODIS image (September 20, 2002) acquired from NASA

History

Glacial History According to Madole (1976), during the latter part of the Pleistocene (~1.8 million years before present - 10,000 years BP) and into the early Holocene (10,000 years BP - present) large valley glaciers were present across most of the higher mountain ranges of Colorado and a small icecap even formed in the northwest part of Rocky Mountain National Park. Valley glaciers in the Front Range were typically 15-25 km long and 1-3 km wide, reaching down to elevations of 2440 to 2745 m. These valley glacier ranged in thickness from 215 to 460 m and the longest was 45 km long (located in the valley of the Cache la Poudre River and fed by the icecap). In Colorado only two Pleistocene glacial advances are recorded on the landscape: Bull Lake and Pinedale (The names come from the Wind River Range where these glacial advances were first identified.). The Bull Lake glaciation is thought to have occurred 125,000 to 50,000 years BP, while the Pinedale glaciation has been dated to 29,000 to 7,600 years BP. Generally the Bull Lake glaciation was more extensive. Additionally there have been three small Holocone (10,000 years BP to present) glacial advances termed, from oldest to youngest, Triple Lakes, Audubon, and Arapaho Peak advances. Collectively these minor advances are termed Neoglaciation, and the largest glacier during these advances was only 1.6 km long. The Arapaho Peak advance is local evidence for the Little Ice Age (the popular name for a period of cooling in the northern hemisphere lasting approximately from the 14th to the mid-19th centuries). Most of the glaciers and perennial ice patches in Colorado today are the tattered remnants of these small Little Ice Age glaciers. Artist's rendering of Rocky Mountain National Park during the late Pleistocene (Rocky Mountain National Park Archives) Early Exploration It was not until late in the 19th century that the presence of glaciers, past or present, in Colorado was recognized. (It is unknown if Native Americans had identified the presence of glaciers in Colorado, but the Ute Indians did made extensive use of high passes in the Rockies (Buchholtz, 1983).) In fact, Mary Dartt (1879), Israel Russell (1885), and Theo Comstock (1886) all made emphatic statements that no glaciers exist in Colorado (Henderson, 1910). Clarence King identified Colorado as having been formerly glaciated, but neither him nor Ferdinand Vandeveer Hayden identified any glaciers in Colorado in their USGS surveys of the American West (Henderson, 1910). The first scientific description of a glacier in Colorado belongs to G.S. Stone of Colorado Springs who described Hallett Glacier (now known as Rowe Glacier) in northern Rocky Mountain National Park in the journal Science in 1887: "The material of the ice-field, though somewhat granular on the surface, is not a mass of snow, but a clear and compact ice. ... The lower parts of the crevasses were filled with snow and broken icicles, ice stalagmites, etc., so that only from twenty to thirty feet can be seen. How much deeper the crevasses really are, is not known; but, from the size and shape of the ice-field, it does not seem probable that the greatest depth of ice exceeds fifty or seventy-five feet." Stone named the glacier Hallett Glacier after W.L. Hallett of Colorado Springs who, in 1883, discovered evidence that he was walking on a glacier and not just a snowfield by stepping into a snow-covered crevasse and nearly falling in. Stone's visit to the glacier confirmed the claims of earlier visits by Hallett and a Mr. Chapin of Hartford, Conn. According to Stone's article, Mr. Chapin was a member of the Appalachian Mountain Club, and first pronounced it to be a true glacier in July 1886. However, according to the National Park Service, Israel Rowe first discovered the glacier while bear hunting in 1880 (Alberts, date unknown). The Park Service renamed the glacier after Rowe in 1932 to avoid confusion with Hallett Peak 15 miles south (near Tyndall Glacier). The first decade of the twentieth century saw an increase in the awareness of glaciers in Colorado. W.T. Lee first described Arapaho Glacier (Colorado's largest) in 1900 in the journal Science. Enos Mills (considered the Father of Rocky Mountain National Park) wrote a guidebook in 1905 that included a map locating Andrews, Hallett, Sprague, and Tyndall glaciers. Isabelle Glacier was discovered by Fred A. Fair in 1908 (Henderson, 1910). Henderson named Fair Glacier after him, which he also discovered. Tyndall Glacier had been identified by 1893 (by Frederick H. Chapin) and Sprague Glacier by 1895 (by Enos Mills). Outside of the Front Range, ice masses or glaciers were described on the northeast side of Blanca Peak in the Sangre de Cristo Range (Siebenthal, 1907) and in various places in the San Juan Mountains (Cross and Whitman, 1905; Hills, 1883). Interestingly, none of these features are present on the USGS topographic maps of the 1950s. Enos Mills, "Father of Rocky Mountain National Park" (Photographer: W.T. Lee; USGS Photo Archives) Explorer and crevasse on Rowe Glacier, August, 25, 1916 (Photographer: W.T. Lee; USGS Photo Archives) Explorers and crevasse on Rowe Glacier, August, 25, 1916 (Photographer: W.T. Lee; NSIDC) Photographs Arapaho Glacier in 1898 (R.S. Brackett, published in Waldrop, R.S. (1964) Arapaho Glacier: A Sixty Year Record. University of Colorado Studies, Series in Geology, No. 3; from NASA Earth Observatory) Arapaho Glacier in 2003 (Tad Pfeffer; from NASA Earth Observatory) Rowe Glacier, August, 25, 1916 (Photographer: W.T. Lee; NSIDC) Rowe Glacier, September 18, 2004 (Photographer: Andy Leach; leachfam.com) Back to Contents

Glaciated Regions

• Front Range

About 48 snow and ice bodies are found in the Front Range with a minimum elevation of 3294 m and maximum elevation of 4068 m, a mean of 3671 m and an area of 2.1 km2. The Front Range contains all of Colorado's 14 officially named glaciers (including Arapaho and Rowe glaciers pictured above). The largest glacier in Colorado is Arapaho Glacier (0.24 km2), located in the central Front Range. The Front Range has 11 of the state's 26 glaciers larger than 0.05 km2and five of the ten largest. It is the only place in Colorado where glaciers have been studied, and to many glaciologists, the only place in the state with true glaciers. Rocky Mountain National Park contains 32 of the Front Range snow and ice features, including 8 of the named glaciers. The remainder of Front Range snow and ice features are in or near the Indian Peaks Wilderness. The tiny St. Mary's Glacier is located southeast of James Peak near I-70. (Glacier outlines in Front Range from USGS 1:24,000 scale topographic maps, created from 1951-1958 aerial photographs) Most of the glaciers and snowfields of the Front Range occur in cirques on the east side of ridges - only 3 features are on the west side of the Continental Divide, all of which are in protected north to east facing cirques. Interestingly, there are also a number of icefields on relatively flat ridgetops. Aerial photo of ice feature on flat ridge above Icefield Pass (north of Hagues Peak). This is the largest feature in Rocky Mountain National Park and the 6th largest in the state. (Photo: Rocky Mountain National Park, September 2001)

Glaciers and snowfields in the Front Range shown in blue.

Andrews Glacier, 2001 (Photographer: John Achuff)

• Medicine Bow Mountains

About 10 snow and ice bodies are found in the Medicine Bow Mountains with a minimum elevation of 3384 m and a maximum elevation of 3793 m, a mean of 3564 m and an area of 0.17 km2. There are no named features, and the largest feature is 0.04 km2. These features were mapped by the USGS from photos taken in 1958. (Glacier outlines in Medicine Bow Mountains from USGS 1:24,000 scale topographic maps, created from 1958 aerial photographs) The glaciers and snowfields of the Medicine Bow Mountains all occur in east-facing cirques near the ridge crest, like most glaciers and snowfields in the state. Presumably all of these features are permanent snowfields or stagnant ice and no active glaciers exist in the Medicine Bow Mountains. However, 9 of the mapped features contain ice on September 13, 1999, USGS air photos, and the feature above Rockhole Lake shows what may be a small crevasse (see lower right). Most features have shown either a modest decrease or little change in area from 1958 to 1999. The two features in the figure below are typical. Many of the features seem to feed rock glaciers as seen in the image below. Two of the larger 1958 mapped ice features in the Medicine Bow Mountains are shown in blue outline on this air photo. Extensive rock glaciers can be seen flowing out of these features. (Photo: USGS, September 13, 1999)	Glaciers and snowfields in the Medicine Bow Range shown in blue
	Snow/ice feature typical of the Medicine Bow Range. This feature is located in the north cirque of Clark Peak and was not mapped by the USGS. (Photographer: Andy Leach; leachfam.com)
	Air photo of possible crevasse on ice feature above Rockhole Lake (Photo: USGS, September 13, 1999)

• Park Range

About 18 snow and ice bodies are found in the Park Range with a minimum elevation of 3256 m and a maximum elevation of 3647 m with a mean of 3462 m and an area of 0.49 km2. There are no named features, and the largest feature is 0.06 km2. These features were mapped by the USGS from photos taken in 1952. (Glacier outlines in Park Range from USGS 1:24,000 scale topographic maps, created from 1952 aerial photographs) The glaciers and snowfields of the Park Range all occur in east- to north-facing cirques near the ridge crest. Presumably all of these features are permanent snowfields or stagnant ice and no glaciers exist. However, most of the mapped features contain ice on 9/13/1999 USGS air photos, and have shown only a modest decrease in area from 1952 to 1999 . No crevasses are visible on the September 13, 1999, USGS air photos. Many of the features seem to feed rock glaciers. The Park Range receives some of the highest annual precipitation in the state (Daly and others, 2003).

Glaciers and snowfields in the Park Range shown in blue.

• Gore Range

About 35 snow and ice bodies are found in the Gore Range with a minimum elevation of 3388 m and a maximum elevation of 4013 m with a mean of 3710 m and an area of 1.49 km2. There are no named features, and the largest feature is 0.20 km2. There are 11 features larger than 0.05 km2. These features were mapped by the USGS from photos taken in 1969 or 1975, depending on location. (Glacier outlines in Gore Range from USGS 1:24,000 scale topographic maps, created from 1969-1975 aerial photographs) The glaciers and snowfields of the Gore Range generally occur in east- to north-facing cirques on the east side of the ridge crest. Presumably most of these features are permanent snowfields or stagnant ice and few, if any, active glaciers exist. However, most of the mapped features contain ice on October 12, 1999, USGS air photos, and have shown only a modest decrease in area from 1969 or 1975 to 1999. No crevasses are visible on the October 12, 1999, USGS air photos, but early season snow covers most ice features. Some of the features seem to feed rock glaciers, and there are extensive rock glaciers found in the Gore Range. The northern Gore Range has more and larger glacier/snowfield features while the southern Gore Range has more and larger rock glaciers. Two ice features on north face of Mount Powell (Photographer: Theron Welch; theronwelch.com) Three ice features on north face of Mount Powell (Photographer: Theron Welch; theronwelch.com)

Glaciers and snowfields of the Gore Range Typical glacier/snowfield change in the Gore Range. Outlines are original USGS mapping (lower feature mapped from 1969 photo, rest of features from 1975). Aerial photo was taken October 12, 1999. Note that early season snowfall has obscured the edges of the ice features. Ground photos show green tint to lake below Peak F, suggesting presence of glacial flour.

• Tenmile Range

Only one snow/ice body is found in the Tenmile Range. It has a minimum elevation of 3896 m and a maximum elevation of 4015 m with a mean of 3959 m and an area of 0.03 km2. This feature was mapped by the USGS from photos taken in 1968. Air photos of the feature dated 9/9/1999 and 10/12/1999 show little evidence of any ice, but there may be a small rock glacier in its place. (Glacier outline in Tenmile Range from USGS 1:24,000 scale topographic maps, created from 1968 aerial photographs) The Tenmile Range contains numerous rock glaciers. The Spruce Creek Rock Glacier, one valley north, is one of the more dramatic examples of a rock glacier in Colorado. It has been studied extensively by Eric Leonard at Colorado College. 1968 outline of single Tenmile Range feature in blue. Air photo is USGS September 9, 1999, and October 12, 1999.

Single mapped icefield in Tenmile/Mosquito Range Air photo of Spruce Creek Rock Glacier (courtesy of USDA-Forest Service and Eric Leonard)

• Sawatch Range

About 25 snow/ice bodies are found in three areas of the Sawatch Range. Elevation ranges from 3293 m to 4290 m with a mean of 3811 m and a total area of 0.35 km2. There are no named features, and the only feature larger than 0.05 km2 is located on Mount Massive (0.52 km2). These features were mapped by the USGS from photos taken in 1964, 1968, or 1975, depending on location. (Glacier outlines in Sawatch Range from USGS 1:24,000 scale topographic maps, created from 1964-1975 aerial photographs) The features of the Sawatch Range tend to be very small and located in southeast to northeast facing cirques near ridgecrests. The 19 features in the Holy Cross Wilderness are generally small, isolated ice patches or ice that feeds rock glaciers. Most have shrunk in size from 1968 to 1999, but still show ice. The large feature in the photo below is the largest in the area and has maintained its size. The features in the Holy Cross are similar to those in the nearby Gore Range. The single feature on Mount Massive is the largest in the Sawatch Range. The aerial photo below indicates it is an ice feature and has grown between 1965 and 1999. This feature is somewhat unique in that it exists on a relatively flat ridgetop with very little topographic shading. It shows no evidence of movement, so it would not be classified as a glacier. The 5 features in the Collegiate Peaks Wilderness are all very small. Based on 1999 air photos all of them have all but disappeared since 1975. However, this region shows a particularly high density of rock glaciers (see photo below).	Glaciers and snowfields in the Sawatch Range shown in blue
Icefields on Holy Cross Ridge. Blue outline is from 1968 topo map. Air photo is USGS October 12, 1999. Ground photos show green tint to Upper Tuhare Lake and lake at lower left of photo, suggesting the presence of glacial flour.	Glaciers and snowfields in the northern Sawatch Range (Holy Cross Wilderness) shown in blue
Icefield on Mount Massive. Blue outline is from 1964 topo map. Air photo is USGS October 12, 1999.	Glacier or snowfield in the central Sawatch Range (Mount Massive Wilderness) shown in blue
Icefield on Huron Peak. Blue outline is from 1975 topo map. Air photo is USGS, October 12, 1999. Note that while extent of ice has decreased significantly, the basin is nearly completely covered by active and relict rock glaciers.	Glaciers and snowfields in the southern Sawatch Range (Collegiate Peaks Wilderness) shown in blue

• San Miguel Mountains

Icefields in the San Miguel Mountains. Blue outlines are from 1952 topo map. Air photo is USGS September 9, 1998. Ice extent has not changed significantly.

Glaciers and snowfields in the San Miguel Mountains shown in blue

• Sierra Blanca

Historically, two glaciers were identified in the Sierra Blanca in the southern Sangre de Cristo Range. C.E. Siebenthal described these features located on the north side of Blanca Peak in 1907:

"The width of the glacier is about 800 feet and its greatest length is about 1,000 feet, although the ice probably extends a considerable distance farther beneath the terminal moraine. The glacier lies in a pocket on the mountain side, and the ice is probably quite thick. A prospecting tunnel, starting in the moraine below the edge of the visible ice, went horizontally in the clear ice for a distance of 115 feet without reaching rock, which, taking into account the slope of the surface, demonstrates a vertical thickness of over 80 feet. The slope of the ice surface is very steep, about 42° - quite too steep for climbing without alpinestock and ice-creepers."

These two features were not mapped on USGS topo maps, but are still present on aerial photos. Their areas appear to have changed little over 95 years.

"Blanca glaciers" from the northeast in 1903 (Photographer: C.E. Siebenthal)

Aerial photo of "Blanca glaciers" (Photo: USGS 9/27/1998)

Fun Facts

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References