Jonathan M. Harbor

Numerical modeling of the development of U-shaped valleys by glacial erosion

The steep-sided valleys and overdeepened basins of alpine landscapes are well-known products of glaciation, yet relatively little is known about how the dynamics of ice flow and glacial erosion interact to give rise to such landforms. By linking a finite-element model for ice flow through a glacier cross section with an erosion model, it is possible to investigate the development of one of the most striking glacial landforms, the U-shaped valley. In addition to providing a detailed understanding of landform development, such modeling provides a way to test current understanding of the controls on glacial sliding and erosion. To simulate valley development, I first model flow through an initial glacier cross section and calculate the glaciological parameters that govern erosion. I then numerically simulate erosion to produce a modified transverse profile, for which a new flow field and erosion pattern are computed. A number of iterations permits examination of the progressive transformation of cross-section form, which can be compared with field data. Model predictions of the cross-section flow field are in close accord with data from the Athabasca Glacier and include marked lateral variations in sliding velocity. With an erosion law dependent on basal velocity, the model predicts the rapid transformation of a V-shaped cross section into a recognizably glacial form over a time period on the order of 10 4 yr and the eventual development of a steady-state, quasi-parabolic glacier cross section. Better agreement with empirical data from glaciated valleys is obtained by including temporal variations in ice discharge, in order to mimic the characteristics of 100,000-yr glacial cycles. The high-discharge phase dominates form development, and, at low discharges, cross-section form is essentially inherited from the central part of the form that developed during the preceding high-discharge phase.

Development of glacial-valley cross sections under conditions of spatially variable resistance to erosion

Abstract A simulation model that examines the development of valley cross-profiles as a result of glacial erosion has been constructed by placing a finite-element model for ice flow within an iterative program that modifies channel cross-section form on the basis of an erosion equation. The simulation model has previously been used to examine how different flow laws, erosion laws and ice discharge histories affect medium-scale landform development. This allows us to better understand the development of glacial landforms, and also provides a critical test for erosion and flow laws. Within the erosion component of the simulation program it is possible to specify spatial variations in bedrock erodibility in order to examine the effect of spatially variable lithologies on form development. As an initial test of form development under these conditions a central area of enhanced erodibility is placed in the valley center. In this case active glacial channels develop that are narrower and deeper than those which occur with homogenous bedrock. This change in form occurs as long as the weaker zone is small enough that the active channel does not eventually narrow to a stage such that it is entirely contained within the weaker material, and as long as it is large enough that it continues to have a significant impact on overall discharge through the section. Form variation occurs because the weaker central zone enhances the lateral gradient of the erosion rate, which is critical for form development. A central area of more erodible bedrock changes not only the form of the active glacial channel, but also the convexity of side slopes that are left above the glacier as it erodes downwards into the landscape. The absence of a classic U-shaped cross section should not be taken, a priori, to suggest either absence of glacial erosion or ineffective glacial erosion. Rather, the combination of active glacial and hillslope processes in a landscape with spatially and temporally variable ice discharge and rock characteristics can create a diverse set of cross-section forms.

Urbanization impacts on surface runoff of the contiguous United States

Urbanization is one of the most important anthropogenic modifications of the global environment (Antrop, 2004; DeFries and Eshleman, 2004; Eshleman, 2004; Foley et al., 2005; Weng, 2002; Wu, 2014). Every urban region in the United States has expanded substantially in area in recent decades (USEPA, 2013). Urbanization presents humans with a dilemma (Foley et al., 2005). On one hand, urban development is essential because it provides convenience of infrastructure, goods and services needed by people, government, economic development, industry, and trade (Foley et al., 2005; Lowry, 1990); on the other hand, land surface modifications occur during the process of urbanization including vegetation reduction, soil compaction, and change from pervious surfaces to impervious surfaces such as roofs, roads, and parking lots (Arnold and Gibbons, 1996; Booth and Jackson, 1997; Schueler, 1994). The consequences of these land surface modifications

Glacial geomorphology of the Altai and Western Sayan Mountains, Central Asia

In this article, we present a map of the glacial geomorphology of the Altai and Western Sayan Mountains, covering an area of almost 600,000 km2. Although numerous studies provide evidence for restricted Pleistocene glaciations in this area, others have hypothesized the past existence of an extensive ice sheet. To provide a framework for accurate glacial reconstructions of the Altai and Western Sayan Mountains, we present a map at a scale of 1:1,000,000 based on a mapping from 30 m resolution ASTER DEM and 15 m/30 m resolution Landsat ETM+ satellite imagery. Four landform classes have been mapped: marginal moraines, glacial lineations, hummocky terrain, and glacial valleys. Our mapping reveals an abundance of glacial erosional and depositional landforms. The distribution of these glacial landforms indicates that the Altai and Western Sayan Mountains have experienced predominantly alpine-style glaciations, with some small ice caps centred on the higher mountain peaks. Large marginal moraine complexes mark glacial advances in intermontane basins. By tracing the outer limits of present-day glaciers, glacial valleys, and moraines, we estimate that the past glacier coverage have totalled to 65,000 km2 (10.9% of the mapped area), whereas present-day glacier coverage totals only 1300 km2 (0.2% of the mapped area). This demonstrates the usefulness of remote sensing techniques for mapping the glacial geomorphology in remote mountain areas and for quantifying the past glacier dimensions. The glacial geomorphological map presented here will be used for further detailed reconstructions of the paleoglaciology and paleoclimate of the region.

Glacial geomorphology of the Shaluli Shan area, southeastern Tibetan Plateau

We present a glacial geomorphological map covering 1.04 × 105 km2 of the Shaluli Shan (Shan = Mountain), southeastern Tibetan Plateau. Using a 90 m digital elevation model from the Shuttle Radar Topography Mission and 15/30 m Landsat Enhanced Thematic Mapper Plus satellite imagery, we have mapped glacial valleys, marginal moraines, hummocky terrain, glacial lineations and ice-scoured terrain. Lineations and scoured areas largely overlap on the low relief granite plateau of the Shaluli Shan and relate to former ice cap glaciation. These landscape features indicate that past ice cap glaciation included basal sliding conditions, and thus warm-based ice. Glacial valleys and marginal moraines are dominant landforms in the high mountain ranges of Shaluli Shan and occur on and fringing the plateau. This glacial geomorphological map forms the basis for paleoglaciological reconstructions of this southeastern Tibetan Plateau region and indicates the former presence of multiple glaciations involving valley glaciers and ice caps. The map is presented at a scale of 1:630,000.

Glacial geomorphology: modeling processes and landforms

Abstract The primary goal of glacial geomorphology is to provide physically-based explanations of the past, present and future impacts of glaciers and ice sheets on landform and landscape development. To achieve this requires the integration of studies of landform with studies of the processes responsible for form development (over a wide range of spatial and temporal scales). During the twentieth century significant improvements in approaches to recognizing and describing glacial landforms have been matched by impressive advances in understanding and modeling ice flow and glacial erosion and deposition processes. At present process models are being tested explicitly in terms of predicting the development of known forms (which also provides new insight into the controls on form development). Evaluations of the implications of deformable beds for process and form development are also being attempted. Finally, we are reassessing long-held beliefs about the significance of glacial action in landform development and sediment production. As we head towards the twenty-first century, glacial geomorphology, will advance through the use of three-dimensional numerical models that include ice flow, basal sliding (with explicit consideration of deformable beds), erosion and deposition processes, and underlying material characteristics. These models will be used to address form evolution and test process models, and will include both the temporal and spatial aspects of form development. Space-based landform recognition, as well as the challenges presented by the concerns of global change, will place heightened emphasis on large-scale problems, which will include reexamination of the basic significance of glacial versus nonglacial action in landform development and sediment production.

CHEMICAL TRAP EFFICIENCY OF A CONSTRUCTION SITE STORM-WATER RETENTION BASIN

Storm-water runoff from construction sites is an important source of nonpoint-source (NPS) pollution in urban areas, and retention basins are widely used on construction sites to control NPS pollution. Although design specifications for such basins may include sediment-trap efficiency requirements, little is known about how well these basins control chemical pollutants such as heavy metals and nutrients. These chemical pollutants exist in both particulate and dissolved forms in storm-water runoff and can change form during transport. Thus, runoff leaving a storm-water basin with little sediment still could contain significant chemical pollution. Data collected during storms for a retention basin in northern Ohio show that inflow and outflow sediment and pollutant loads often display similar temporal trends. For a storm event with a low (19.7%) sediment-trap efficiency (TE), lead, chromium, and cadmium had TEs of -0.4%, -55%, and -27.3%, respectively. The basin had 72.9% lead and 56.1% reactive phosphorus ...

A Capstone Course in Environmental Geosciences.

Many geology departments have increased the number and scope of environmental courses they offer, or even instituted new majors, in response to changing student interests and the increasing demand for environmental professionals with geoscience skills. The geology major typically includes a senior capstone course that integrates material covered in other coursework; however, most traditional capstone courses were not designed with environmental applications of geosciences in mind. At Purdue University, we have developed a capstone course specifically for our Environmental Geosciences major. This projects-based course stresses small-group identification, analysis, and solution of real-world geo-environmental problems at a local scale. This mimics work a student might later perform as a consultant, in an interdisciplinary graduate research team, or in an industrial- or government-agency setting. The course focuses on use of existing knowledge drawn from past coursework, rapid acquisition of new project-related skills and knowledge, professional-level presentation in written and oral forms, real-world problem identification, teamwork skills, working under tight deadlines, and provision of products or solutions appropriate for a client. This prepares students for the immediate demands of post-college employment, as well as developing lifelong learning skills to respond to evolving future needs. Students consider this a challenging course but respond well to the collaborative, service-learning framework as a transition to post-college employment.

MODELING POTENTIAL IMPACTS OF LAND DEVELOPMENT ON SEDIMENT YIELDS

To assist land-use managers in addressing the problem of erosion, a computer simulation model (SEDCAD) can be used to determine the effectiveness of well-applied erosion-control practices in reducing the loss of soil from actively developing sites. The program includes procedures based on a modified version of the Universal Soil Loss Equation, which is widely used by water resource managers to estimate soil erosion rates over a range of spatial scales. For a construction site in northeastern Ohio, the computer program SEDCAD was used to estimate the changes in off-site sediment delivery that occur when the soil on the site is completely exposed as a result of clearing, grading, and other construction activities. Assuming application of erosion-control best-management practices, ranging from the use of straw mulch to the use of a sediment basin, SEDCAD simulation results indicate that proper management practices can reduce sediment delivery to wetlands adjacent to this site to pre-development levels. This ...

Late Pleistocene Glaciations on Qianhu Mountain, Northwest Yunnan Province, China

Abstract ianhu ountain, situated southeast of the ibetan lateau, is a key location for testing the role of tectonic uplift in controlling the response of mountain glaciations to climate change in western hina. The mountain has distinctive glacial landforms and deposits, including cirques, peaks, arêtes, lateral moraines and terminal moraines above 3500 m a.s.l., and these morphologic features suggest a clear sequence of landscape‐forming events during one or more glacial cycles. Optically stimulated luminescence dating reveals that the glacial deposits record events from the last glacial maximum (LGM, ∼22.2 ± 1.9 ka), the middle stage of the last glacial cycle (marine isotope stage 3 (MIS3), 37.3 ± 3.7 — 45.6 ± 4.3 ka) and possibly an earlier stage of the last glacial cycle. The glacial extent in the middle stage of the last glacial cycle is larger than that in the . This may reflect a larger increase in outh sia summer monsoon precipitation during than during the . The glacial sequences preserved on ianhu Mountain indicate a briefer history of glaciation here compared with mountains to the northwest, which experienced more and earlier uplift in association with uplift of the ibetan lateau. This suggests that climatic and tectonic factors both play a part in controlling the number and extent of glaciations in western hina.