We report detailed chemical and isotopic data from a subglacial siliceous deposit on andesitic be... more We report detailed chemical and isotopic data from a subglacial siliceous deposit on andesitic bedrock recently exposed by glacier retreat. Whereas a single, <1 μm, Si-rich layer covers the highly polished bedrock on the up-glacier (stoss) surfaces, distinct, lithified deposits commonly occur at the lee of small bedrock protuberances, on a scale <0.1 meter. The deposit is millimeters in thickness and consists of laminae tens to hundreds microns thick that differ from one another in color, rock-fragment abundance and chemical composition. Ca-rich laminae that are sufficiently enriched in uranium (~2–50 ppm) to permit U-series isotopic analysis suggest that the subglacial deposit formed 10–20 ka, much earlier than previously assumed. We conclude that (1) the siliceous deposit persisted for at least 10 000 years despite the intervening erosion and weathering, (2) distinct episodes of formation due to significant changes in hydrology and water chemistry are recorded in the deposit...
Subsurface temperatures in polar environments control geomorphic, hydrologic, and biologic proces... more Subsurface temperatures in polar environments control geomorphic, hydrologic, and biologic processes and ground ice stability. Most studies of the thermal regime in permafrost areas have been developed for the Arctic where interest and concern focus on permafrost thawing. In contrast, this study focuses on soils in the McMurdo Dry Valleys of Antarctica where conditions are much colder and drier, and long-term persistence of ground ice is of interest including as an analog site for Mars. The soil temperature in Beacon Valley, one of the McMurdo Dry Valleys, has been modeled using the surface temperature, measured heat capacity, and temperature-dependent thermal conductivity and compared to continuous, high-resolution measurements of temperatures for a decade down to 19.6-m depth. For the temperature range of À47.9 to 7.5°C at our study site, the heat capacity of the dry soil ranges from 580 to 690 J • kg À1 • K À1 , thermal conductivity from 0.22 to 0.27 W • m À1 • K À1 , and the calculated thermal diffusivity from 0.23 to 0.25 mm 2 /s. Both the finite difference method and the finite volume method are used to solve the 1-D heat diffusion equation; the finite volume method-modeled temperature most closely approximates the measured temperature at all depths with average differences ranging from 0.01 to 0.03°C. The latent heat contribution of documented episodic snowmelt events and of modeled changes in ice content due to condensation or sublimation is negligible. This study can be applied readily to thermal regimes of similar systems where subsurface temperature measurements are not available such as on Mars.
Recent micrographs of smooth, glacially abraded silicic bedrock reveal an amorphous coating layer... more Recent micrographs of smooth, glacially abraded silicic bedrock reveal an amorphous coating layer adhering to the bedrock, with structures that tie its formation to glacial abrasion. What remains unclear is whether this coating is formed by the physical comminution of bedrock, resulting in amorphous material with a bedrock composition, or by chemical dissolution of silicate minerals followed by precipitation of an amorphous layer enriched in silica and depleted in cations relative to the bedrock. Here, we report the composition and formation age of the amorphous coatings in Yosemite National Park, California, USA. The coatings are depleted in base cations (50%-90%) and enriched in silica (10%-50%) as well as trace Fe and U (4-to 100fold) relative to the bedrock, reflecting dissolution by and precipitation from subglacial waters. The 234 U/ 238 U activity ratio of the amorphous layer is 200%-600% above secular equilibrium, reflecting a surficial U source enriched by α-recoil processes and consistent with the 234 U enrichment observed in subglacial waters. The 230 Th/ 238 U activity ratio is 30%-100% below secular equilibrium and records Th-U fractionation in subglacial waters at 30-10 ka, consistent with coating formation during the Last Glacial Maximum (LGM). These amorphous coatings are subglacial precipitates that record the chemical weathering of silicates beneath glaciers during the LGM. Collectively, these observations link silicate dissolution and amorphous silica production to physical processes at the glacier bed, a result that may have significant implications for the global Si and CO 2 budgets on glacial-interglacial time scales.
Mars Science Laboratory (MSL) Curiosity rover data are used to describe the morphology of desicca... more Mars Science Laboratory (MSL) Curiosity rover data are used to describe the morphology of desiccation cracks observed in ancient lacustrine strata at Gale crater, Mars, and to interpret their paleoenvironmental setting. The desiccation cracks indicate subaerial exposure of lacustrine facies in the Sutton Island member of the Murray formation. In association with ripple cross-stratification and possible eolian cross-bedding, these facies indicate a transition from longer-lived perennial lakes recorded by older strata to younger lakes characterized by intermittent exposure. The transition from perennial to episodically exposed lacustrine environments provides evidence for local to regional climate change that can help constrain Mars climate models.
The Mars Science Laboratory Mast camera and Descent Imager investigations were designed, built, a... more The Mars Science Laboratory Mast camera and Descent Imager investigations were designed, built, and operated by Malin Space Science Systems of San Diego, CA. They share common electronics and focal plane designs but have different optics. There are two Mastcams of dissimilar focal length. The Mastcam-34 has an f/8, 34 mm focal length lens, and the M-100 an f/10, 100 mm focal length lens. The M-34 field of view is about 20°× 15°with an instantaneous field of view (IFOV) of 218 μrad; the M-100 field of view (FOV) is 6.8°× 5.1°with an IFOV of 74 μrad. The M-34 can focus from 0.5 m to infinity, and the M-100 from~1.6 m to infinity. All three cameras can acquire color images through a Bayer color filter array, and the Mastcams can also acquire images through seven science filters. Images are ≤1600 pixels wide by 1200 pixels tall. The Mastcams, mounted on the~2 m tall Remote Sensing Mast, have a 360°azimuth and~180°elevation field of regard. Mars Descent Imager is fixed-mounted to the bottom left front side of the rover at~66 cm above the surface. Its fixed focus lens is in focus from~2 m to infinity, but out of focus at 66 cm. The f/3 lens has a FOV of~70°by 52°across and along the direction of motion, with an IFOV of 0.76 mrad. All cameras can acquire video at 4 frames/second for full frames or 720p HD at 6 fps. Images can be processed using lossy Joint Photographic Experts Group and predictive lossless compression. Plain Language Summary Paper describes the Mast cameras and Descent Imager on the Mars Science Laboratory Curiosity rover. Cameras take 2 megapixel color images that can be compressed in both JPEG lossy and predictive lossless format. One of the two Mastcams has a 34 mm lens, equivalent to a consumer camera 35 mm lens, and the other has a 100 mm lens, similar to consumer camera telephoto lens. The descent imager has a very wide angle lens (~90°) and takes wide angle pictures. The Mast cameras are mounted on an azimuth elevation mast so they can scan around the rover and into the sky. The Descent camera always points down. The Mast cameras have different filters to allow for scientific color imaging as well as standard color imaging as performed by consumer cameras.
Glacial quarrying remains enigmatic despite being long recognized as a primary, perhaps the domin... more Glacial quarrying remains enigmatic despite being long recognized as a primary, perhaps the dominant, process by which glaciers erode bedrock. The rate-limiting process appears to be subglacial rock fracture due to ice-induced mechanical stresses. To study this erosional process, a simple model of quarrying is developed for a glacier sliding over a periodic series of bedrock steps. Consideration of the balance of forces at the ice/rock interface and of the rate of cavity closure permits evaluation of ice-induced stresses on bedrock surfaces. The resulting stress distribution where ice loads are most concentrated near the corner of bedrock steps is evaluated using a simple elastic solution for the state of stress in a loaded quarter-plane. It is then used to determine whether fractures in the rock will grow, and to estimate the rate of progressive crack growth. Based on these crack-growth rates, an index of the quarrying rate is then calculated as a function of glaciological variable...
The water and sediment output from Vitus Lake, in Front of Bering Glacier, was monitored starting... more The water and sediment output from Vitus Lake, in Front of Bering Glacier, was monitored starting in July 1994, Instrumentation was placed in the lake outlet to record stage, turbidity, conductivity and temperature and velocity of flow of river water. Two outburst floods punctuated the termination of the 1993–94 Bering Glacier surge in August 1994. The better-documented flood lasted about 10 d, during which the flood discharge averaged 1100 m3s−1, in excess of normal discharge (1550 m3s−1) during this part of the ablation season, and about 9.5 × 108m3of water drained from Bering Glacier. The excess water volume discharged during this flood corresponds to a 0.4 m thick layer of water extending over the 2500 km2of Bering Glacier that was surging in early summer. The suspended-sediment flux from Vitus Lake during the summer of 1994 was two orders of magnitude less than rates of sediment production by other fast-moving glaciers in southern Alaska. This implies that most of the sediment ...
The glacier sliding theory of Nye is modified to include the effect of solutes in subglacial rege... more The glacier sliding theory of Nye is modified to include the effect of solutes in subglacial regelation waters on the sliding process. Motivation for this development stems from studies of subglacially formed chemical deposits that appear to be widespread on rock surfaces recently exposed by retreating temperate glaciers. These deposits indicate clearly that considerable local concentration of solutes commonly occurs subglacially as a result of the selective rejection of solutes into the melt during the freezing associated with regelation sliding. Because solutes accumulate where regelation waters refreeze, they tend to lower the temperature there and hence inhibit the heat transport away from these areas that is essential for regelation sliding. For a simple sinusoidal bed and solute distribution in the regelation water film, the modified theory shows that a maximum excess of solutes of, for example, several millimoles/1 of dissolved CaCo3 along lee surfaces relative to stoss surfa...
The spatial pattern of the formerly active processes of water flow, cavitation, abrasion, dissolu... more The spatial pattern of the formerly active processes of water flow, cavitation, abrasion, dissolution, and precipitation at the base of a small cirque glacier has been reconstructed by detailed mapping of surficial features on recently deglaciated limestone bedrock near the glacier terminus. Our interpretation of these features, which reflect basal conditions averaged over a period of several or several tens of years, leads us to the following conclusions:1.A nearly continuous, non-arborescent network of cavities and incised channels existed and probably acted as the primary drainage of melt waters. This network evolved through time as many channels were filled, perhaps intermittently, by basal ice.2.At least 20% of the glacier sole was separated from the bed by water-filled cavities. The rest of the glacier–rock interface characteristically comprises a very thin water film.3.Abrasion was locally intensified, relative to chemical alteration, in 5–10 m wide zones paralleling the ice-...
Preliminary results of a quantitative model of glacial abrasion are presented. The analysis, whic... more Preliminary results of a quantitative model of glacial abrasion are presented. The analysis, which is constructed within a framework of modern glaciological views of processes near to the bed, is aimed at modeling abrasion under a temperate glacier whose basal layers contain only occasional rock fragments. It does not simulate abrasion by debris-rich ice or by subglacial drift. Calculations of abrasion-rates reduce to evaluations of the forces pressing rock fragments against the glacier bed and of the rates at which they are moved along the bed. The estimated viscous drag induced by ice flow toward the bed due to basal melting is generally the dominant contribution to this contact force. Although the analysis shares several important elements with the pioneering study of Boulton ([c1974]), sufficient fundamental differences in the modeling lead to distinctly different conclusions. Several new results are noteworthy: (1) other parameters being equal, abrasion will tend to be fastest ...
Recent studies of subglacially precipitated carbonate deposits and associated solutional furrows ... more Recent studies of subglacially precipitated carbonate deposits and associated solutional furrows have provided interesting new insight on subglacial water films, as well as on chemical exchange at the glacier bed. Considerable information on the film thickness and its temporal and spatial variability has been gained by analyzing several properties of subglacial carbonate deposits including: (1) the morphology of surface features aligned parallel to ice flow, (2) the laminated structure, and (3) the size distribution of fine rock fragments presumably transported in the film prior to their incorporation in the deposits. Chemical analyses of water from pro-glacial streams, together with calculations of CaCO3solubility and mass balance, show that the channelized water is chemically distinct from the film water in which CaCO3precipitates, and that subglacial precipitation is not possible where there is a considerable water flux through the film in excess of that associated with regelatio...
ABSTRACTTo explore links between glacier dynamics, sediment yields and the accumulation of glacia... more ABSTRACTTo explore links between glacier dynamics, sediment yields and the accumulation of glacial sediments in a temperate setting, we use extensive glaciological observations for Columbia Glacier, Alaska, and new oceanographic data from the fjord exposed during its retreat. High-resolution seismic data indicate that 3.2 × 108m3of sediment has accumulated in Columbia Fjord over the past three decades, which corresponds to ~5 mm a−1of erosion averaged over the glaciated area. We develop a general model to infer the sediment-flux history from the glacier that is compatible with the observed retreat history, and the thickness and architecture of the fjord sediment deposits. Results reveal a fivefold increase in sediment flux from 1997 to 2000, which is not correlated with concurrent changes in ice flux or retreat rate. We suggest the flux increase resulted from an increase in the sediment transport capacity of the subglacial hydraulic system due to the retreat-related steepening of th...
Abstract : Patterned ground is ubiquitous in Arctic and alpine areas. To improve understanding of... more Abstract : Patterned ground is ubiquitous in Arctic and alpine areas. To improve understanding of this phenomenon, we developed extensive field instrumentation that has been recording principal soil properties over the past four years. The resulting data constitute the first quantitative year-round records of important seasonal process such as freezing, thawing, frost heaving, and settling in the active layer in a sorted circle area. The data provide unprecedented insight into the long-term dynamics of active sorted soil patterns. We have complemented our field research with analytical and numerical studies of sorted pattern formation. Deterministic and stochastic analyses of pattern development in the absence of significant soil deformation reveal strong textural instabilities; stones initially distributed at random through the soil tend to migrate quickly toward domains slightly richer in stones, which eventually leads to the distinct sorting characteristic of diverse forms of patterned ground. Our numerical model of sorted stripe formation successfully simulates stripe development, and sheds considerable light on formative process. We have also developed a novel model to assess buoyancy forces that arise in the thaw process, and may be responsible for the long-term circulatory soil motion documented in sorted circles in Spitsbergen.
We report detailed chemical and isotopic data from a subglacial siliceous deposit on andesitic be... more We report detailed chemical and isotopic data from a subglacial siliceous deposit on andesitic bedrock recently exposed by glacier retreat. Whereas a single, <1 μm, Si-rich layer covers the highly polished bedrock on the up-glacier (stoss) surfaces, distinct, lithified deposits commonly occur at the lee of small bedrock protuberances, on a scale <0.1 meter. The deposit is millimeters in thickness and consists of laminae tens to hundreds microns thick that differ from one another in color, rock-fragment abundance and chemical composition. Ca-rich laminae that are sufficiently enriched in uranium (~2–50 ppm) to permit U-series isotopic analysis suggest that the subglacial deposit formed 10–20 ka, much earlier than previously assumed. We conclude that (1) the siliceous deposit persisted for at least 10 000 years despite the intervening erosion and weathering, (2) distinct episodes of formation due to significant changes in hydrology and water chemistry are recorded in the deposit...
Subsurface temperatures in polar environments control geomorphic, hydrologic, and biologic proces... more Subsurface temperatures in polar environments control geomorphic, hydrologic, and biologic processes and ground ice stability. Most studies of the thermal regime in permafrost areas have been developed for the Arctic where interest and concern focus on permafrost thawing. In contrast, this study focuses on soils in the McMurdo Dry Valleys of Antarctica where conditions are much colder and drier, and long-term persistence of ground ice is of interest including as an analog site for Mars. The soil temperature in Beacon Valley, one of the McMurdo Dry Valleys, has been modeled using the surface temperature, measured heat capacity, and temperature-dependent thermal conductivity and compared to continuous, high-resolution measurements of temperatures for a decade down to 19.6-m depth. For the temperature range of À47.9 to 7.5°C at our study site, the heat capacity of the dry soil ranges from 580 to 690 J • kg À1 • K À1 , thermal conductivity from 0.22 to 0.27 W • m À1 • K À1 , and the calculated thermal diffusivity from 0.23 to 0.25 mm 2 /s. Both the finite difference method and the finite volume method are used to solve the 1-D heat diffusion equation; the finite volume method-modeled temperature most closely approximates the measured temperature at all depths with average differences ranging from 0.01 to 0.03°C. The latent heat contribution of documented episodic snowmelt events and of modeled changes in ice content due to condensation or sublimation is negligible. This study can be applied readily to thermal regimes of similar systems where subsurface temperature measurements are not available such as on Mars.
Recent micrographs of smooth, glacially abraded silicic bedrock reveal an amorphous coating layer... more Recent micrographs of smooth, glacially abraded silicic bedrock reveal an amorphous coating layer adhering to the bedrock, with structures that tie its formation to glacial abrasion. What remains unclear is whether this coating is formed by the physical comminution of bedrock, resulting in amorphous material with a bedrock composition, or by chemical dissolution of silicate minerals followed by precipitation of an amorphous layer enriched in silica and depleted in cations relative to the bedrock. Here, we report the composition and formation age of the amorphous coatings in Yosemite National Park, California, USA. The coatings are depleted in base cations (50%-90%) and enriched in silica (10%-50%) as well as trace Fe and U (4-to 100fold) relative to the bedrock, reflecting dissolution by and precipitation from subglacial waters. The 234 U/ 238 U activity ratio of the amorphous layer is 200%-600% above secular equilibrium, reflecting a surficial U source enriched by α-recoil processes and consistent with the 234 U enrichment observed in subglacial waters. The 230 Th/ 238 U activity ratio is 30%-100% below secular equilibrium and records Th-U fractionation in subglacial waters at 30-10 ka, consistent with coating formation during the Last Glacial Maximum (LGM). These amorphous coatings are subglacial precipitates that record the chemical weathering of silicates beneath glaciers during the LGM. Collectively, these observations link silicate dissolution and amorphous silica production to physical processes at the glacier bed, a result that may have significant implications for the global Si and CO 2 budgets on glacial-interglacial time scales.
Mars Science Laboratory (MSL) Curiosity rover data are used to describe the morphology of desicca... more Mars Science Laboratory (MSL) Curiosity rover data are used to describe the morphology of desiccation cracks observed in ancient lacustrine strata at Gale crater, Mars, and to interpret their paleoenvironmental setting. The desiccation cracks indicate subaerial exposure of lacustrine facies in the Sutton Island member of the Murray formation. In association with ripple cross-stratification and possible eolian cross-bedding, these facies indicate a transition from longer-lived perennial lakes recorded by older strata to younger lakes characterized by intermittent exposure. The transition from perennial to episodically exposed lacustrine environments provides evidence for local to regional climate change that can help constrain Mars climate models.
The Mars Science Laboratory Mast camera and Descent Imager investigations were designed, built, a... more The Mars Science Laboratory Mast camera and Descent Imager investigations were designed, built, and operated by Malin Space Science Systems of San Diego, CA. They share common electronics and focal plane designs but have different optics. There are two Mastcams of dissimilar focal length. The Mastcam-34 has an f/8, 34 mm focal length lens, and the M-100 an f/10, 100 mm focal length lens. The M-34 field of view is about 20°× 15°with an instantaneous field of view (IFOV) of 218 μrad; the M-100 field of view (FOV) is 6.8°× 5.1°with an IFOV of 74 μrad. The M-34 can focus from 0.5 m to infinity, and the M-100 from~1.6 m to infinity. All three cameras can acquire color images through a Bayer color filter array, and the Mastcams can also acquire images through seven science filters. Images are ≤1600 pixels wide by 1200 pixels tall. The Mastcams, mounted on the~2 m tall Remote Sensing Mast, have a 360°azimuth and~180°elevation field of regard. Mars Descent Imager is fixed-mounted to the bottom left front side of the rover at~66 cm above the surface. Its fixed focus lens is in focus from~2 m to infinity, but out of focus at 66 cm. The f/3 lens has a FOV of~70°by 52°across and along the direction of motion, with an IFOV of 0.76 mrad. All cameras can acquire video at 4 frames/second for full frames or 720p HD at 6 fps. Images can be processed using lossy Joint Photographic Experts Group and predictive lossless compression. Plain Language Summary Paper describes the Mast cameras and Descent Imager on the Mars Science Laboratory Curiosity rover. Cameras take 2 megapixel color images that can be compressed in both JPEG lossy and predictive lossless format. One of the two Mastcams has a 34 mm lens, equivalent to a consumer camera 35 mm lens, and the other has a 100 mm lens, similar to consumer camera telephoto lens. The descent imager has a very wide angle lens (~90°) and takes wide angle pictures. The Mast cameras are mounted on an azimuth elevation mast so they can scan around the rover and into the sky. The Descent camera always points down. The Mast cameras have different filters to allow for scientific color imaging as well as standard color imaging as performed by consumer cameras.
Glacial quarrying remains enigmatic despite being long recognized as a primary, perhaps the domin... more Glacial quarrying remains enigmatic despite being long recognized as a primary, perhaps the dominant, process by which glaciers erode bedrock. The rate-limiting process appears to be subglacial rock fracture due to ice-induced mechanical stresses. To study this erosional process, a simple model of quarrying is developed for a glacier sliding over a periodic series of bedrock steps. Consideration of the balance of forces at the ice/rock interface and of the rate of cavity closure permits evaluation of ice-induced stresses on bedrock surfaces. The resulting stress distribution where ice loads are most concentrated near the corner of bedrock steps is evaluated using a simple elastic solution for the state of stress in a loaded quarter-plane. It is then used to determine whether fractures in the rock will grow, and to estimate the rate of progressive crack growth. Based on these crack-growth rates, an index of the quarrying rate is then calculated as a function of glaciological variable...
The water and sediment output from Vitus Lake, in Front of Bering Glacier, was monitored starting... more The water and sediment output from Vitus Lake, in Front of Bering Glacier, was monitored starting in July 1994, Instrumentation was placed in the lake outlet to record stage, turbidity, conductivity and temperature and velocity of flow of river water. Two outburst floods punctuated the termination of the 1993–94 Bering Glacier surge in August 1994. The better-documented flood lasted about 10 d, during which the flood discharge averaged 1100 m3s−1, in excess of normal discharge (1550 m3s−1) during this part of the ablation season, and about 9.5 × 108m3of water drained from Bering Glacier. The excess water volume discharged during this flood corresponds to a 0.4 m thick layer of water extending over the 2500 km2of Bering Glacier that was surging in early summer. The suspended-sediment flux from Vitus Lake during the summer of 1994 was two orders of magnitude less than rates of sediment production by other fast-moving glaciers in southern Alaska. This implies that most of the sediment ...
The glacier sliding theory of Nye is modified to include the effect of solutes in subglacial rege... more The glacier sliding theory of Nye is modified to include the effect of solutes in subglacial regelation waters on the sliding process. Motivation for this development stems from studies of subglacially formed chemical deposits that appear to be widespread on rock surfaces recently exposed by retreating temperate glaciers. These deposits indicate clearly that considerable local concentration of solutes commonly occurs subglacially as a result of the selective rejection of solutes into the melt during the freezing associated with regelation sliding. Because solutes accumulate where regelation waters refreeze, they tend to lower the temperature there and hence inhibit the heat transport away from these areas that is essential for regelation sliding. For a simple sinusoidal bed and solute distribution in the regelation water film, the modified theory shows that a maximum excess of solutes of, for example, several millimoles/1 of dissolved CaCo3 along lee surfaces relative to stoss surfa...
The spatial pattern of the formerly active processes of water flow, cavitation, abrasion, dissolu... more The spatial pattern of the formerly active processes of water flow, cavitation, abrasion, dissolution, and precipitation at the base of a small cirque glacier has been reconstructed by detailed mapping of surficial features on recently deglaciated limestone bedrock near the glacier terminus. Our interpretation of these features, which reflect basal conditions averaged over a period of several or several tens of years, leads us to the following conclusions:1.A nearly continuous, non-arborescent network of cavities and incised channels existed and probably acted as the primary drainage of melt waters. This network evolved through time as many channels were filled, perhaps intermittently, by basal ice.2.At least 20% of the glacier sole was separated from the bed by water-filled cavities. The rest of the glacier–rock interface characteristically comprises a very thin water film.3.Abrasion was locally intensified, relative to chemical alteration, in 5–10 m wide zones paralleling the ice-...
Preliminary results of a quantitative model of glacial abrasion are presented. The analysis, whic... more Preliminary results of a quantitative model of glacial abrasion are presented. The analysis, which is constructed within a framework of modern glaciological views of processes near to the bed, is aimed at modeling abrasion under a temperate glacier whose basal layers contain only occasional rock fragments. It does not simulate abrasion by debris-rich ice or by subglacial drift. Calculations of abrasion-rates reduce to evaluations of the forces pressing rock fragments against the glacier bed and of the rates at which they are moved along the bed. The estimated viscous drag induced by ice flow toward the bed due to basal melting is generally the dominant contribution to this contact force. Although the analysis shares several important elements with the pioneering study of Boulton ([c1974]), sufficient fundamental differences in the modeling lead to distinctly different conclusions. Several new results are noteworthy: (1) other parameters being equal, abrasion will tend to be fastest ...
Recent studies of subglacially precipitated carbonate deposits and associated solutional furrows ... more Recent studies of subglacially precipitated carbonate deposits and associated solutional furrows have provided interesting new insight on subglacial water films, as well as on chemical exchange at the glacier bed. Considerable information on the film thickness and its temporal and spatial variability has been gained by analyzing several properties of subglacial carbonate deposits including: (1) the morphology of surface features aligned parallel to ice flow, (2) the laminated structure, and (3) the size distribution of fine rock fragments presumably transported in the film prior to their incorporation in the deposits. Chemical analyses of water from pro-glacial streams, together with calculations of CaCO3solubility and mass balance, show that the channelized water is chemically distinct from the film water in which CaCO3precipitates, and that subglacial precipitation is not possible where there is a considerable water flux through the film in excess of that associated with regelatio...
ABSTRACTTo explore links between glacier dynamics, sediment yields and the accumulation of glacia... more ABSTRACTTo explore links between glacier dynamics, sediment yields and the accumulation of glacial sediments in a temperate setting, we use extensive glaciological observations for Columbia Glacier, Alaska, and new oceanographic data from the fjord exposed during its retreat. High-resolution seismic data indicate that 3.2 × 108m3of sediment has accumulated in Columbia Fjord over the past three decades, which corresponds to ~5 mm a−1of erosion averaged over the glaciated area. We develop a general model to infer the sediment-flux history from the glacier that is compatible with the observed retreat history, and the thickness and architecture of the fjord sediment deposits. Results reveal a fivefold increase in sediment flux from 1997 to 2000, which is not correlated with concurrent changes in ice flux or retreat rate. We suggest the flux increase resulted from an increase in the sediment transport capacity of the subglacial hydraulic system due to the retreat-related steepening of th...
Abstract : Patterned ground is ubiquitous in Arctic and alpine areas. To improve understanding of... more Abstract : Patterned ground is ubiquitous in Arctic and alpine areas. To improve understanding of this phenomenon, we developed extensive field instrumentation that has been recording principal soil properties over the past four years. The resulting data constitute the first quantitative year-round records of important seasonal process such as freezing, thawing, frost heaving, and settling in the active layer in a sorted circle area. The data provide unprecedented insight into the long-term dynamics of active sorted soil patterns. We have complemented our field research with analytical and numerical studies of sorted pattern formation. Deterministic and stochastic analyses of pattern development in the absence of significant soil deformation reveal strong textural instabilities; stones initially distributed at random through the soil tend to migrate quickly toward domains slightly richer in stones, which eventually leads to the distinct sorting characteristic of diverse forms of patterned ground. Our numerical model of sorted stripe formation successfully simulates stripe development, and sheds considerable light on formative process. We have also developed a novel model to assess buoyancy forces that arise in the thaw process, and may be responsible for the long-term circulatory soil motion documented in sorted circles in Spitsbergen.
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