Glaciology Commons^™

Climate On The Blanca Massif, Sangre De Cristo Mountains, Colorado, Usa, During The Last Glacial Maximum, Keith A. Brugger, Eric M. Leonard, Kurt A. Refsnider, Peter Dolan

Geology Publications

Temperature-index modeling is used to determine the magnitude of temperature depression on the Blanca Massif, Colorado, required to maintain steady-state mass balances of nine reconstructed glaciers at their extent during the Last Glacial Maximum (LGM). The mean temperature depression thus determined is ~8.6 +0.7/−0.9 degrees C where the uncertainties account for those inherent in the glacier reconstructions, in model parameters (e.g., melt factors), and possible modest changes in LGM precipitation. Associated equilibrium-line altitudes (ELAs) exhibit a statistically significant directional dependency being lower toward the north and east. Under the assumption that regional temperature change was uniform, required changes in precipitation …

Late Pleistocene Glaciation In The Mosquito Range, Colorado, U.S.A.: Chronology And Climate, Keith A. Brugger, Benjamin J.C. Laabs, Alexander Reimers, Noah Bensen

Geology Publications

New cosmogenic ¹⁰Be surface exposure ages from seventeen moraine boulders in the Mosquito Range suggest that glaciers were at their late Pleistocene (Pinedale) maximum extent at ~21–20 ka, and that ice recession commenced prior to ~17 ka. These age limits suggest that the Pinedale Glaciation was synchronous within the Colorado Rocky Mountain region. Locally, the previous (Bull Lake) glaciation appears to have occurred no later than 117 ka, possibly ~130 ka allowing for reasonable rock weathering rates. Temperature-index modeling is used to determine the magnitude of temperature depression required to maintain steady-state mass balances of seven reconstructed glaciers at …

Pinedale Glacial History Of The Upper Arkansas River Valley: New Moraine Chronologies, Modeling Results And Geologic Mapping, Avriel D. Schweinsberg, Jason P. Briner, Ralph R. Shroba, Joseph M. Licciardi, Eric M. Leonard, Keith A. Brugger, Charles M. Russell

Geology Publications

This field trip guidebook chapter outlines the glacial history of the upper Arkansas River valley, Colorado, and builds on a previous GSA field trip to the same area in 2010. The following will be presented: (1) new cosmogenic 10Be exposure ages of moraine boulders from the Pinedale and Bull Lake glaciations (Marine Isotope Stages 2 and 6, respectively) located adjacent to the Twin Lakes Reservoir, (2) numerical modeling of glaciers during the Pinedale glaciation in major tributaries draining into the upper Arkansas River, (3) discharge estimates for glacial-lake outburst floods in the upper Arkansas River valley, and (4) 10Be ages …

Dye Tracing To Determine Flow Properties Of Hydrocarbon-Polluted Rabots Glaciär, Kebnekaise, Sweden, Caroline C. Clason, C. Coch, J. Jarsjö, Keith A. Brugger, P. Jansson, G. Rosqvist

Geology Publications

Over 11 000 L of kerosene was deposited on the surface of Rabots glaciär on the Kebnekaise Massif, northern Sweden, following the crash of a Royal Norwegian Air Force aircraft in March 2012. An environmental monitoring programme was subsequently commissioned, including a series of dye tracing experiments during the 2013 melt season, conducted to investigate the transport of pollutants through the glacier hydrological system. This experimental set-up provided a basis from which we could gain new insight into the internal hydrological system of Rabots glaciär. Results of dye tracing experiments reveal a degree of homogeneity in the topology of the …

Changes In The Geometry And Volume Of Rabots Glaciär, Sweden, 2003-2011: Recent Accelerated Volume Loss Linked To More Negative Summer Balances, Keith A. Brugger, Latysha Pankratz

Geology Publications

Terminus geometry, ice margins, and surface elevations on Rabots glaciär were measured using differential GPS during summer 2011 and compared with those similarly measured in 2003. Glacier length over the eight years decreased by ∼105 m corresponding to 13 m a−1, a rate consistent with ice recession over the last several decades. Measured changes in surface elevations show that between 2003 and 2011 the glacier’s volume decreased by ∼27.6 ± 2.6 × 106 m3, or 3.5± 0.3 × 106 m3 a−1. This compares favorably with an estimate of −28.1 ± 2.6 × 106 m3 based on a mass-balance approach. The …

Instruments And Methods: A Method For Recording Ice Ablation Using A Low-Cost Ultrasonic Rangefinder, M. Len Keeler, Keith A. Brugger

Geology Publications

We have adapted inexpensive ultrasonic rangefinders to measure ablation rates on the surface of a glacier.While ultrasonic rangers are commercially available for this purpose, our goal was to utilize rangefinders typically used in hobby robotics without significantly compromising performance. To correct for environmental factors that affect the speed of sound we use two ultrasonic rangefinders, one focused on a fixed target. Measurements of ablation correlate well with manual measurements with an uncertainty of about 3 cm, suggesting an accuracy comparable with other non-manual methods of recording ablation. The limitations of our rangefinder include those inherent in commercially available units as …

Effect Of A Cold Margin On Ice Flow At The Terminus Of Storglaciaren, Sweden: Implications For Sediment Transfer, Keith A. Brugger, Peter L. Moore, Neal R. Iverson, Denis Cohen, Thomas S. Hooyer, Peter Jansson

Geology Publications

The cold-based termini of polythermal glaciers are usually assumed to adhere strongly to an immobile substrate and thereby supply significant resistance to the flow of warm-based ice upglacier. This compressive environment is commonly thought to uplift basal sediment to the surface of the glacier by folding and thrust faulting. We present model and field evidence from the terminus of Storglaciaren, Sweden, showing that the cold margin provides limited resistance to flow from up-glacier. Ice temperatures indicate that basal freezing occurs in this zone at 10⁻¹ –10⁻² ma⁻¹, but model results indicate that basal motion at rates …

Climate In The Southern Sawatch Range And Elk Mountains, Colorado, U.S.A., During The Last Glacial Maximum: Inferences Using A Simple Degree-Day Model, Keith A. Brugger

Geology Publications

Equilibrium-line altitudes (ELAs) were determined from reconstructions of 22 paleoglaciers at their extent during the local last glacial maximum (LGM) using the accumulation-area method. LGM ELAs thus derived ranged from 2980 to 3560 m and follow a statistically significant regional trend of rising ~4.5 m km^-1 to the east. Two approaches using a degree-day model were used to infer LGM climate by finding plausible combinations of temperature and precipitation change that (1) would be required to lower ELAs to their mean LGM values in both the Taylor Park/eastern Elk Mountains region and western Elk Mountains, and (2) provide steady-state …

Cosmogenic 10be And 36cl Ages From Late Pleistocene Terminal Moraine Complexes In The Taylor River Drainage Basin, Central Colorado, U.S.A., Keith A. Brugger

Geology Publications

Cosmogenic surface-exposure ages from boulders on a terminal moraine complex establish the timing of the local last glacial maximum (LGM) in the Taylor River drainage basin, central Colorado. Five zero-erosion ¹⁰Be ages have a mean of 19.5±1.8 ka while that for three ³⁶Cl ages is 20.7±2.3 ka. Corrections for modest rates (∼1 mm ka⁻¹) of boulder surface erosion result in individual and mean ages that are generally within 2% of their zero-erosion values. Both the means and the range in ages of individual boulders are consistent with those reported for late Pleistocene moraines elsewhere in the …

The Non-Synchronous Response To Rabots Glaciar And Storglaciaren, Northern Sweden, To Recent Climate Change: A Comparative Study, Keith A. Brugger

Geology Publications

Rabots Glaciar and Storglaciaren, two small valley glaciers in the Swedish Arctic, have not behaved synchronously in response to recent climate change. Both glaciers advanced late in the 19th century and then began to retreat in response to an approximately 1 degree C warming that occurred around 1910. By the mid-1980s the terminus and volume of Storglaciaren had essentially stabilized, so it may have completed its response to the earlier warming. In contrast, ongoing thinning and retreat of Rabots Glaciar are substantial and suggest its response time is considerably longer. A time-dependent numerical model was used to investigate each glacier’s …

Rock Glaciers In Central Colorado, U.S.A., As Indicators Of Holocene Climate Change, Kurt A. Refsnider, Keith A. Brugger

Geology Publications

We measured thalli diameters of the lichen Rhizocarpon subgenus Rhizocarpon on 48 individual lobes of 18 rock glaciers and rock glacier complexes in the Elk Mountains and Sawatch Range of central Colorado. Cumulative probability distribution and K-means clustering analyses were used to separate lichen thalli measurements into statistically-distinct groups, each interpreted as representing a discrete episode of rock glacier activity driven by an interval of cooler climate. Lichen ages for these episodes were assigned using a growth curve developed for Rhizocarpon geographicum in the nearby Front Range. An early Neoglacial episode, ca. 3080 yr BP, is correlative to other glacial …

Late Pleistocene Climate Inferred From The Reconstruction Of The Taylor River Glacier Complex, Southern Sawatch Range, Colorado, Keith A. Brugger

Geology Publications

Ice surface topography of a late Pleistocene glacier complex, herein named the Taylor River Glacier Complex (TRGC), was reconstructed on the basis of detailed mapping of glacial landforms combined with analyses of aerial photos and topographic maps. During the last glacial maximum (LGM), the TRGC covered an area of 215 km² and consisted of five valley or outlet glaciers that were nourished by accumulation in cirques basins and/or upland ice fields.

Equilibrium-line altitudes (ELAs) for the glaciers of the TRGC were estimated using the accumulation-area ratio method, assuming that ratio to be 0.65 ± 0.05. ELAs thus derived ranged …

Variation In Glacier Length And Ice Volume Of Rabots Glaciar, Sweden, In Response To Climate Change, 1910–2003, Keith A. Brugger, Kurt A. Refsnider, Matthew F. Whitehill

Geology Publications

Historical records, photographs, maps and measurements were used to determine changes in the length, geometry and volume of Rabots Glaciar, Sweden, in response to a warming that occurred early in the 20th century.