General Site Information:(40º 3' N; 105º 36 ' W)
Niwot Ridge is located approximately 35 km west of Boulder, Colorado, with the entire study site lying above 3000 m elevation. There is a cirque glacier (Arikaree Glacier), extensive alpine tundra, a variety of glacial landforms, glacial lakes and moraines, cirques and talus slopes, patterned ground, and permafrost. The research area is bounded on the west by the Continental Divide, with runoff on the two sides being destined for the Colorado and Mississippi Rivers. The alpine study area is reached by an unimproved road from the Mountain Research Station (2895 m) which leads to within 2 km of the main tundra research site, the Saddle (3528 m). The D-1 research site (3739 m), for which climate records are continuous from 1952, lies a farther 3 km from the road head. The Martinelli study area (3380 m) is located 1 km southwest of the Saddle, in the forest-tundra ecotone. The Green Lakes Valley lies immediately south of the western half of Niwot Ridge. It includes the Arikaree Glacier at its head (3798 m), and the wetland, Green Lake 4, and Albion research sites. The Green Lakes Valley and Martinelli sites are all within the City of Boulder Watershed which is closed to public access. Niwot Ridge, including the main alpine study site, is part of the Roosevelt National Forest and has been designated a Biosphere Reserve (United Nations Educational, Scientific and Cultural Organization, UNESCO) and an Experimental Ecology Reserve (USDA Forest Service). A context-sensitive topographic relief map can be used to access the scenic views of the areas indicated above, as well as several others.
A-1: (40º 00' 36'' N; 105º 22' 32'' W; 2199 m)
A-1 is located in a lower montane forest, 29 km east of the Continental Divide. Topographic setting: ridge-top. On US Forest Service land. Climate data begins 1952 with some major gaps. Temperature is most complete, with precipitation and solar radiation data existing during shorter time periods.
B-1: (40º 01' 20'' N; 105º 25' 45'' W; 2621 m)
B-1 is located in an upper montane forest, 22.5 km east of the Continental Divide. Topographic setting: ridge-top. On US Forest Service land. Climate data begins 1952 with some major gaps. Temperature is most complete, with precipitation and solar radiation data existing during shorter time periods.
C-1: (40º 02' 09'' N; 105º 32' 09'' W; 3021 m)
C-1 is located in a subalpine Forest, 9.7 km east of the Continental Divide. Topographic setting: ridge-top. Climate data completeness good from 1953 to present. Climate parameters measured include temperature, relative humidity, solar radiation, barometric pressure, wind speed and direction, precipitation, soil moisture and temperature, and snow depth. At this site are also atmospheric and ecological research operations including the NCRS Snotel site, NOAA CMDL Carbon (CO2) and Halocarbon (anthroponenic greenhouse gases and staospheric ozone depletors, and surface ozone) measurements, National Weather Service precipitation gage, NOAA Climate Research Network (CRN) weather station, Ameriflux tower (forest ecology and atmospheric flux).
Soddie: (40º 02' 52'' N; 105º 34' 15'' W; 3345 m)
The Soddie Laboratory is located below treeline, at 3345 m, in an open meadow surrounded by ribbon forest which prevents lateral inputs of blowing snow. The site is on a 10º southwest facing slope. The meadow has an array of snow lysimeters and a meteorological tower which are connected to an adjacent underground laboratory [Erickson, 2004].
Saddle: (40º 03' 17'' N; 105º 35' 21'' W; 3528 m)
The Saddle site is an alpine tundra site, located 5.6 km from the Continental Divide. Topographic setting: ridge-top, but in a shallow saddle between east and west knolls. There is a 10,000 sq ft tundra laboratory at Niwot Ridge which serves as a staging area for research in all weather conditions. In addition, there is an 80 sq ft subnivean laboratory equipped with snow melt lysimeters that drain into dedicated tipping buckets. These laboratories have year-round motorized access 120-volt line power. There is an Aerometrics wet--chemistry precipitation collector as part of the National Atmospheric Deposition Program (NADP), which has operated continuously since 1984 and is the highest site in the entire NADP network. The timing, duration, and amount of snow cover has been manipulated since 1994 with a 2.6x60 m snowfence, providing a proxy for climate change. There are several meteorological stations at the Saddle site. Climate data completeness is good from 1981 to present. Climate parameters measured include temperature, relative humidity, solar radiation, barometric pressure, wind speed and direction, precipitation, soil moisture and temperature. NOAA measures surface ozone as well.
Soils are Cryochrepts and are approximately 2.0 m in depth over granitic parent material. Soil C in the top 100 mm of soil ranges from 130 to 200 g/kg and soil N pools range from 9 to 15 g/kg [Burns, 1980].
Subnivean: (40º 03' 15'' N; 105º 35' 27'' W; 3535 m)
The Subnivean site is located within the Saddle on Niwot Ridge. The instrument site is located in a relatively flat area above treeline within a broad saddle of the ridge. The high elevation and exposure of Niwot Ridge and typically dry atmospheric conditions result in large clear-sky atmospheric transmissivity, increased solar insolation, low magnitudes of incident longwave radiation, low air temperatures, and high wind velocities. The depth of snow accumulation on Niwot Ridge is extremely variable, being influenced by the interaction of high wind velocities and topography. Windswept areas devoid of snow may be found immediately adjacent to depositional areas with accumulations in excess of 8 m.
D-1: (40º 03' 34'' N; 105º 37' 0'' W; 3739 m)
D-1 is an Alpine Tundra site, located 2.6 km from the Continental Divide. This is the highest continuously operating weather station in North America. Topographic setting: ridge-top. Climate data completeness good from 1953 to present. Climate parameters measured include temperature, relative humidity, solar radiation, barometric pressure, wind speed and direction, precipitation, soil moisture and temperature.
Albion Townsite: (40º 02' 34'' N; 105º 35' 32'' W; 3259 m)
Topographic setting: on the valley floor, on North Boulder Creek. Data begins in 2003 and is comprised of temperature, wind speed and direction, stream flow and stream depth.
Green Lake 4: (40º 03' 17'' N; 105º 37' 7'' W; 3570 m)
Topographic setting: on the valley floor, approximately 400 meters south of Green Lake 4. Climate data begins in 1986. Temperature has been taken continuously and other measurements with shorter records include solar radiation, wind speed and direction, and relative humidity.
T-van: (40º 03' 11'' N; 105º 35' 11'' W; 3523 m)
Topographic setting: ridge-top, but on a south facing slope. Air samples have been taken here, in flasks, for NOAA CMDL since 1963. These flasks are analysed for the same compounds as at C1
Arikaree Glacier: (40º 02' 56'' N; 105º 38' 24'' W; 3814 m)
Topographic setting: at the base of the Arikaree Glacier, on a small moraine, in the valley floor at the head of the Green Lakes Valley approximately 0.5 km east of the Continental Divide. Climate data begins in 1986. Temperature has been taken continuously and other measurements with shorter records include solar radiation, wind speed and direction, and relative humidity.
Green Lakes Valley: (40º 03' N; 105º 37' W; 4084 - 3380 m)
Named for a series of shallow paternoster lakes, the Green Lakes Valley is the headwaters of North Boulder Creek and lies within the City of Boulder Watershed. There are two sections to the catchment, separated by a glaciated valley-step between Green Lake 3 and 4:
The upper basin:
The continental, high mountain climate of Green Lakes Valley has been recorded continuously at the D-1 meteorological station on Niwot Ridge for over 40 years and for shorter periods on the valley floor [Greenland, 1989]. Mean annual temperature at D-1 is -3.7 C [Williams, 1996]. South-facing slopes of the Green lakes Valley are warmer than north-facing slopes, which are underlain by discontinuous permafrost [Ives, 1973].
Almost 80% of the approximately 1000 mm of recorded annual precipitation falls as snow [Caine, 1996]. The bulk snow pack temperature remains below 0 deg. C until late spring, introducing a lag in the hydrological cycle by concentrating the release of melt water in a short, intense period of runoff [Caine, 1996].
The 9-ha Arikaree glacier sits at the head of the valley and is the source of North Boulder Creek. The outflow of the Arikaree glacier drains into Green Lake 5 (GL5).
The lower valley:
The 8-ha Martinelli catchment represents a snow-field dominated catchment
Above Green Lake 5 and extending to the Continental Divide, the Silver Plume quartz monzonite is a light to pinkish gray, coarse-grained, equigranular to porphyritic rock with distinctive white orthoclase phenocrysts up to several cm in length and etched into high relief on weathered surfaces [White, 1981]. Silver Plume quartz monzonite is variable in composition but in general is comprised of microcline, quartz, and feldspar with lesser amounts of biotite and muscovite [Gamble, 1976]. The Audubon-Albion stock, exposed along the north side of Green Lake 5 and extending to the high point of Niwot Ridge, is monzonitic to quartz monzonitic in composition, dark-gray in color, and medium-grained texture consisting of plagioclase, hornblende, pyroxene, quartz, and minor biotite. A fault runs south from the Audubon-Albion stock on Niwot Ridge through GL5 and along the north slope of Kiowa Peak, through and above RG5.
The rocks exposed on the surface of RG5 are angular to subangular, variable in size from cobbles to boulders, and primarily gneissic with minor schistose layers. Gneisses exposed along the active front contain layers that have been propylitically altered and are primarily composed of epidote with minor chlorite, calcite, and pyrite. The origin of the hydrothermal fluids that caused this alteration is unclear, but the rock glacier is located at the edge of the Lake Albion mining district. Within a kilometer of RG5, the Snowy Range vein produced lead, gold, and silver in the early 1900s. Alternatively, the fault that projects under the rock glacier may have been a channel for these fluids, or this mineral assemblage could result from a low grade metamorphic overprinting from the intrusion of the Audubon-Albion stock.
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Diurnal variations in the quality of water draining from an alpine snowpack.
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Streamflow patterns in the alpine environment of North Boulder Creek,
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Zeitschrift fur Geomorphologie, 104:27-42.
Caine, N. 2001.
Geomorphic systems of Green Lakes Valley.
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Ph.D. Dissertation, University of Colorado, Boulder.
Gable, D.J. and Madole, R.F. 1976.
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Types and rates of alpine mass movement, west edge of Boulder County,
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