David Bahr

David Bahr
University of Colorado Boulder | CUB · Institute of Arctic and Alpine Research (INSTAAR)

About

50
Publications
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Introduction
Skills and Expertise

Publications

Publications (50)
Article
Full-text available
While the terms ‘glacier’ and ‘ice cap’ have distinct morphological meanings, no easily defined boundary or transition distinguishes one from the other. Despite this, the exponent of the power law function relating volume to surface area differs sharply for glaciers and ice caps, suggesting a fundamental distinction beyond a smoothly transitioning...
Article
Full-text available
Volume-area power law scaling, one of a set of analytical scaling techniques based on principals of dimensional analysis, has become an increasingly important and widely used method for estimating the future response of the world’s glaciers and ice caps to environmental change. Over 60 papers since 1988 have been published in the glaciological and...
Article
Full-text available
Volume-area power law scaling, one of a set of analytical scaling techniques based on principals of dimensional analysis, has become an increasingly important and widely-used method for estimating the future response of the world's glaciers and ice caps to environmental change. Over sixty papers since 1988 have been published in the glaciological a...
Article
Full-text available
Estimating a glacier's volume by inferring properties at depth (e.g. bed topography or basal slip) from properties observed at the surface (e.g. area and slope) creates a calculation instability that grows exponentially with the size of the glacier. Random errors from this inversion instability can overwhelm all other sources of error and can corru...
Data
Most glaciers and ice caps (GIC) are out of balance with the current climate. To return to equilibrium, GIC must thin and retreat, losing additional mass and raising sea level. Because glacier observations are sparse and geographically biased, there is an undersampling problem common to all global assessments. Here, we further develop an assessment...
Article
Full-text available
Most glaciers and ice caps (GIC) are out of balance with the current climate. To return to equilibrium, GIC must thin and retreat, losing additional mass and raising sea level. Because glacier observations are sparse and geographically biased, there is an un-dersampling problem common to all global assessments. Here, we further develop an 5 assessm...
Article
Full-text available
Estimating a glacier's volume by inferring properties at depth from properties observed at the surface creates an instability that grows exponentially with the size of the glacier. Random errors from this instability can overwhelm the volume calculation unless problematic short spatial wavelengths are specifically excluded. Volume-area scaling inhe...
Article
Full-text available
A single large glacier can contain tens of millions of times the mass of a small glacier. Nevertheless, very small glaciers (with area ≤1 km2) are so numerous that their contribution to the world's total ice volume is significant and may be a notable source of error if excluded. With current glacier inventories, total global volume errors on the or...
Article
Full-text available
A single large glacier can contain hundreds of millions of times the mass of a small glacier. Nevertheless, small glaciers are so numerous that their contribution to the world's total ice volume is significant and may be a notable source of error if excluded. With current glacier inventories, total volume errors on the order of 10 % are possible at...
Article
Most glaciers and ice caps (GIC) are out of balance with the current climate. In order to return to equilibrium, these GIC must retreat to higher elevations, losing mass and raising sea level. The required mass losses can be derived from the accumulation-area ratio (AAR), the fractional glacier area where accumulation exceeds ablation. Here, we pre...
Conference Paper
Glaciers (including the Ice Caps) are major contributors to the observed Sea Level Rise both regionally and globally. We have reasonably good estimates of small scale contributions and contributions from selected regions, and also gross estimates of global contributions. Gaps in knowledge are known and not all of them can be closed. Yet, the number...
Article
Regularly spaced bumps that arise on ski slopes defy intuition by migrating uphill, even though skiers and snow move downhill.
Article
Full-text available
Since the mid-19th century, most glaciers have been losing area and volume. This loss of area has not been homogeneous in time and space, and direct observations are sparse, making regional and global estimates of glacier change difficult. This paper focuses on developing a single index for monitoring glacier change, one that would be particularly...
Article
No single flow model can simulate all possible glaciers and ice sheets without violating fundamental tenets of computational science. The root cause is not one of numerical sophistication, precision or accurate initial conditions. Instead, using flow and transport as data transmission, glaciers inadvertently function as information processors. This...
Article
One of the most easily measured dimensions of a glacier, the accumulation area, is linked to future changes in glacier volume and consequent changes in sea level. Currently observed accumulation areas are too small, forcing glaciers to lose 27% of their volume to attain equilibrium with current climate. As a result, at least 184 ± 33 mm of sea-leve...
Article
Despite significant efforts, obesity continues to be a major public health problem, and there are surprisingly few effective strategies for its prevention and treatment. We now realize that healthy diet and activity patterns are difficult to maintain in the current physical environment. Recently, it was suggested that the social environment also co...
Article
Sediment compaction and corresponding porosity variations can be modeled by a simple exponential with depth. The porosity solution is derived analytically as a complicated function of pore water pressure, but the underlying form is shown to approximate an exponential except near the surface where the behavior is linear. Even though the analytical s...
Article
Full-text available
Measurements of the deformation of a dense array of boreholes in Worthington Glacier, Alaska, show that the glacier moves with generally bed-parallel motion. Strain in the 200 m deep valley glacier is constant near the surface but follows a nonlinear vertical profile below a depth of about 120 m. By a depth of 180 m, the octahedral strain rate reac...
Article
Full-text available
Correlations between suspended sediment load rating parameters, river basin morphology, and climate provide information about the physical controls on the sediment load in rivers and are used to create predictive equations for the sediment rating parameters. Long-term time-averaged values of discharge, suspended load, flow duration, flow peakedness...
Article
A simple theoretical model demonstrates that some amount of randomness in snow and ice mass balance is sufficient to reproduce empirically observed power law and exponential distributions of snow patch and glacier sizes. No other assumptions about the Underlying topography or snow accumulation and ablation processes are necessary to extract this im...
Article
Vigilance in flocks can be described and modelled as a plausible set of local interactions between neighbouring birds. Each bird in the modelled flock chooses to feed or to scan based solely on whether or not its neighbours are feeding or scanning. This simple model has the ability both to reproduce observations that have not been previously explai...
Article
Full-text available
Previous work on the relation between glaeier volume and area and on accumulation area ratios suggests that balance rates measured at the glacier terminus are not constant or random from glacier to glacier but instead scale with glacier length. Using mass-balance data from a collection of 68 valley and cirque glaciers, we show that the terminus mas...
Article
To develop new strategies for global mass-balance monitoring, data for the period 1961-90 have been compiled for 80 glaciers with a variety of mass-balance and morphological parameters. This dataset is significantly larger than that used in previous studies. This allows us to check the mass-balance data for both strong and weak correlations with di...
Article
Previous work on the relation between glacier volume and area and on accumulation area ratios suggests that balance rates measured at the glacier terminus are not constant or random from glacier to glacier but instead scale with glacier length. Using mass-balance data from a collection of 68 valley and cirque glaciers, we show that the terminus mas...
Article
To develop new strategies for global mass-balance monitoring, data for the period 1961–90 have been compiled for 80 glaciers with a variety of mass-balance and morphological parameters. This dataset is significantly larger than that used in previous studies. This allows us to check the mass-balance data for both strong and weak correlations with di...
Article
Full-text available
The spatial and temporal evolution of collective behavior in large populations is simulated with a cellular automaton model and predicted with a statistical mechanical analytical theory of macro‐sociological behavior. The numerical cellular automaton simulations show that the type of collective behavior observed in a group depends sensitively on th...
Article
The process of opinion formation leading to collective behavior in large groups is modeled with a probabilistic and statistical mechanical theory of micro‐sociological behavior. By assuming that the probability of making a given decision is proportional to the number of people who have made the same decision, this theory of micro‐interactions predi...
Article
Full-text available
A simple interpretation of the traditional definitions of glacier and ice sheet response time (e.g., thickness divided by mass balance rate, h/b) suggests that larger glaciers respond more slowly than small glaciers to a perturbation in climate. However, with reasonable choices for mass balance behavior, a scaling analysis shows that the response t...
Article
Full-text available
Numerical experiments were made using a time-dependent nonlinear finite element model of glacier flow to seek confirmation of theoretical predictions made in the companion to this paper [Bahr et al., this issue]. The theoretical analysis indicates that under conditions of equal gradients in mass balance along the glacier surface (∂b/∂x), other vari...
Article
Full-text available
Measurements of water flow through a sinusoidal fracture were undertaken to compare sinusoidal flow with parallel plate flow. Flow rates were measured through a fracture with an amplitude of 1.02 mm and a wavelength of 5.08 mm, with vertical separation ranging from 0.21 mm to 0.71 mm, and for Reynolds numbers (Re) ranging from 0.05 to 58. In additi...
Article
Full-text available
Ice volumes are known for only a few of the roughly 160,000 glaciers worldwide but are important components of many climate and sea level studies which require water flux estimates. A scaling analysis of the mass and momentum conservation equations shows that glacier volumes can be related by a power law to more easily observed glacier surface area...
Article
Many problems in global climate and Earth systems science require knowledge of regional- or global-scale distributions of glacier properties, which includes mass balance, ice velocity, flux, thickness, volume, and surface area, among others. With roughly 160,000 glaciers worlwide, obtaining information on the global probability distributions of mos...
Article
Full-text available
An analysis of hundreds of mountain and valley glaciers in the former Soviet Union and the Alps shows that characteristic glacier widths scale as characteristic glacier lengths raised to an exponent of 0.6. This is in contrast to most previous analyses which implicitly of explicitly assumed scaling exponents of either 0 or 1. The exponent 0.6 impli...
Article
An analysis of hundreds of mountain and valley glaciers in the former Soviet Union and the Alps shows that characteristic glacier widths scale as characteristic glacier lengths raised to an exponent of 0.6. This is in contrast to most previous analyses which implicitly of explicitly assumed scaling exponents of either 0 or 1. The exponent 0.6 impli...
Article
The multiple processes which control motion at the bed of glaciers are too heterogeneous to be modeled directly, but a simple stick-slip slider-block model of a glacier bed allows a statistical mechanical treatment of the physics beneath thin and shallow sloped glaciers. The technique may reconcile apparently contradictory field observations of the...
Article
Flow velocities and stresses within a glacier are determined by inverting known surface velocities with a specified glacier geometry. The surface velocities depend only weakly on the unknown velocities at the bed of a glacier, so the inversion is illposed and unstable. This instability causes both numerical computation errors and data errors to gro...
Article
Full-text available
Glaciers, like rivers, have a branching structure which can be characterized by topological trees or networks. Probability distributions of various topological quantities in the networks are shown to satisfy the criterion for self-similarity, a symmetry structure which might be used to simplify future models of glacier dynamics. Two analytical meth...
Article
Full-text available
Global aqd regional syntheses of glacier melt and runoff are needed for under- standing present and future sea-level rise, as well as for hydrological and climato- logical analyses. Observational data on glacier areas are needed for modeling gla- cier-climate interactions and runoff, but are available for only a few regions. Data on the distributio...
Article
At one time or another, who among us has not marveled at the beauty of the snow and ice-covered Alps, or admired the tenacity of polar explorers and the adventurous spirits of climbers on the glacier-clad summits of the high Himalaya? The fascination of distant ice covered expanses has enlisted more than a few recruits into the ranks of glaciologis...
Article
The physics behind the iceberg calving process is poorly understood, but by using a simple fracturing criterion based on the accumulation and coupling of many microcracks, the complicated mechanics of calving can be simulated by a set if percolation rules. Calving simulations with this simple percolation model give results which are consistent with...
Article
A lattice Boltzmann technique for modeling Navier–Stokes fluid flow is extended to allow steady-state simulations of glaciers and other slow-flowing solids. The technique is based on a statistical mechanical representation of flowing ice as a set of particles (populations) which translate and collide on a face-centered cubic lattice. The average tr...
Article
A lattice Boltzmann technique for modeling Navier–Stokes fluid flow is extended to allow steady-state simulations of glaciers and other slow-flowing solids. The technique is based on a statistical mechanical representation of flowing ice as a set of particles (populations) which translate and collide on a face-centered cubic lattice. The average tr...
Article
To study the dynamics of ice sheets and glaciers, velocities at the bed of a glacier must be measured directly or calculated using data gathered from boreholes and surface surveys. Boreholes to the bed are expensive and time-consuming to drill, so the determination of basal velocity is almost exclusively by numerical inversion of velocities observe...
Article
To study the dynamics of ice sheets and glaciers, velocities at the bed of a glacier must be measured directly or calculated using data gathered from boreholes and surface surveys. Boreholes to the bed are expensive and time-consuming to drill, so the determination of basal velocity is almost exclusively by numerical inversion of velocities observe...
Article
A simple interpretation of the traditional definitions of glacier and ice sheet response time (e.g., thickness divided by mass balance rate, h/) suggests that larger glaciers respond more slowly than small glaciers to a perturbation in climate. However, with reasonable choices for mass balance behavior, a scaling analysis shows that the response t...
Article
Thesis (Ph. D.)--University of Colorado, 1993. Includes bibliographical references (leaves [128]-130).