Glacial Processes Research Articles

Numerically simulating alpine landscapes: The geomorphologic consequences of incorporating glacial erosion in surface process models

A numerical model that simulates the evolution of glaciated mountain landscapes is presented. By employing a popular, sliding based, glacial erosion model, many common glacial landforms are created. The numerical model builds on earlier work as it is fully two-dimensional and employs the first order forcing on mountain evolution. These forcings include tectonic uplift, isostasy, hillslope processes, fluvial processes, and glacial processes. A climate-dependent model of ice dynamics is employed to determine ice coverage and ice flux. Two simulations are presented; one with generic model parameters, and a second with parameters that correspond to conditions in the Southern Alps of New Zealand. Landforms that are produced by the model include climate climate-dependent elevation lowering, similar to what might be expected by a “glacial buzz-saw”, valley overdeepening, terminal moraines, and valley retreat. The model also predicts that current rates of sedimentation are higher than the long-term average, and that several tens of thousands of years are required for the landscape to adjust to a change in the dominant erosional forcing. Therefore, glaciated orogens are unlikely to achieve topographic steady state over Milankovitch timescales.

Rock avalanches that travel onto glaciers and related developments, Karakoram Himalaya, Inner Asia

Catastrophic rock slope failures in rugged terrain commonly generate rock avalanches. When these occur in glacier basins the extent of landslide run out and its emplacement geometry are affected by movement over ice. Substantial modifications of glacier activity and sedimentation can follow. Ice activity leads to rapid modification, transport and dispersal of landslide debris. The nature of these interactions is described from observations over 20 years at Bualtar Glacier in the Karakoram. In August 1986 rock avalanches descended onto the ablation zone of the glacier. Their moisture content and patterns of deposition were affected by travel over ice. Glacier movement increased sharply at and below the rock avalanche deposits and, within a few months, the glacier surged. A second surge occurred 2 years later. Major slope failures and debris flows were triggered beyond the ice margins, and ponded melt water led to small outburst floods. By 2005 the landslide material had been transported some 9 km, about one third of this distance in the surges. Eventually it was fully reworked to become less readily distinguishable from other heavy supraglacial debris. A large area of thickened ice persisted where the debris reduced ablation; a positive impact on mass balance equivalent to a 20% increase in annual accumulation. However, it occurred as a moving segment of the ablation zone. In 10 years it had, in effect, replaced the mass transferred in the surges. Data for the mid-1980s indicate the rock avalanches exceeded pre-existing supraglacial debris by roughly five times and, over a 30 year period, will equal almost 500 years of normal supraglacial transport to the glacier margins. Other impacts of the episode suggest a doubling of this contribution to denudation. Similar developments were observed at three other glaciers where recent rock avalanches occurred and at twenty-one prehistoric rock avalanches newly identified as having spread over glaciers. It seems inadequate to treat such events only as singular extremes, or the landslide and glacial processes separately. Here they are interpreted as contributing to ‘disturbance regime’ landscapes, whose history reflects episodic and regionally specific responses to strong interference among different earth surface processes. They generate polygenetic deposits and landforms that are morphologically complex. Individual episodes involve decades to millennia; their numbers and repetition can over-ride or redirect geotectonic and climatic conditions. It is suggested they are major, but hitherto misread or neglected, elements of landform evolution in the Karakoram and, perhaps, in other high mountains.

The Ascraeus Mons fan-shaped deposit: Volcano–ice interactions and the climatic implications of cold-based tropical mountain glaciation

Amazonian-aged fan-shaped deposits extending to the northwest of each of the Tharsis Montes in the Tharsis region on Mars have been interpreted to have originated from mass-wasting, volcanic, tectonic and/or glacial processes. We use new data from MRO, MGS, and Odyssey to characterize these deposits. Building on recent evidence for cold-based glacial activity at Pavonis Mons and Arsia Mons, we interpret the smaller Ascraeus fan-shaped deposit to be of glacial origin. Our geomorphological assessment reveals a number of characteristics indicative of glacial growth and retreat, including: (1) a ridged facies, interpreted to be composed of drop moraines emplaced during episodic glacial advance and retreat, (2) a knobby facies, interpreted to represent vertical downwasting of the ice sheet, and (3) complex ridges showing a cusp-like structure. We also see evidence of volcano–ice interactions in the form of: (1) an arcuate inward-facing scarp, interpreted to have formed by the chilling of lava flows against the glacial margin, (2) a plateau feature, interpreted to represent a subglacial eruption, and (3) knobby facies superimposed on flat-topped flows with leveed channels, interpreted to be subglacial inflated lava flows that subsequently drained and are covered by glacial till. We discuss the formation mechanisms of these morphologies during cold-based glacial activity and concurrent volcanism. On the basis of a Mid- to Late-Amazonian age (250–380 Ma) established from crater size-frequency distribution data, we explore the climatic implications of recent glaciation at low latitudes on Mars. GCM results show that increased insolation to the poles at high obliquities (>45°) forces sublimation of polar ice, which is transported to lower latitudes and deposited on the flanks of the Tharsis Montes. We assess how local orographic effects, the mass balance of the glacier, and the position of equilibrium line altitudes, all played a role in producing the observed geomorphologies. In doing so, we outline a glacial history for the evolution of the Ascraeus Mons fan-shaped deposit and compare its initiation, growth and demise with those of Arsia Mons and Pavonis Mons.

The demise of the Last Interglacial recorded in isotopically dated speleothems from the Alps

The transition from interglacial to glacial climate has attracted much attention in paleoclimatic research, partly because orbital forcing dictates that such a return to a new ice age is inescapable (albeit in the distant future only). The detailed series of steps that leads to glacial inceptions remains poorly understood, however, and studies of past glacial inceptions are often compromised by incomplete records, imprecise chronological control, and/or uncertainties associated with proxy-transfer functions. Here we present results from U–Th-dated speleothems from a cave in the Austrian Alps (Entrische Kirche cave) which grew continuously between ca 127 and 114 ka and intermittently also during subsequent stadials and interstadials. The alpine setting of this cave is prone to periglacial and glacial processes as well as temperature and precipitation changes which are recorded in these cave deposits. We use high-resolution stable isotope data to constrain paleoenvironmental changes associated with the demise of the Last Interglacial, unprecedented in detail for central Europe. Peak interglacial conditions are characterized by high δ 18O values and high growth rates from ca 127 to 124 ka. A major drop in δ 18O by 3‰ occurred at ca 118 ka, which coincided with cold event C26 in the North Atlantic. This isotopic shift, which occurred at or close to isotopic equilibrium, cannot be explained by simple uniform cooling. Modelling suggests that enhanced seasonality, dominated by significant changes in winter precipitation, are required to reconcile the isotope data with the fact that calcite deposition continued across the MIS 5e/d transition (i.e., no cave freezing). This period of enhanced seasonality lasted for several millennia during which the catchment area of the cave remained geomorphologically stable and ice free. Eventually, speleothem growth terminated at ca 114 ka, which is in line with widespread ice-rafting in the North Atlantic (cold event C24) and the onset of fully stadial conditions during MIS 5d.

Late Quaternary stratigraphy and sedimentology of Orphan Basin: Implications for meltwater dispersal in the southern Labrador Sea

Orphan Basin is a deep-water basin on the continental margin off Newfoundland, which throughout the late Quaternary received proglacial sediment from local ice that crossed the continental shelf. Sediment from more distant sources was transported southward in the Labrador Current as proglacial plumes and in icebergs. Five sedimentary facies related to glacial processes are distinguished in cores recovered from Orphan Basin: hemipelagic sediment, nepheloid-layer deposits (layered mud), beds rich in ice-rafted detritus (IRD), sand and mud turbidites, and glaciogenic debris-flow deposits. IRD-rich beds correspond to periods of intensified iceberg calving, and layered mud, turbidites, and glaciogenic debris-flow deposits with glacial meltwater discharge. In the Late Wisconsinan, eight periods of meltwater discharge and iceberg calving from the Newfoundland ice sheet are interpreted from the sediment facies in Orphan Basin. These discharges coincide with the terminations of the colder periods of the D–O cycles recorded in Greenland ice cores. The oldest minor meltwater event (27.5–28.5 cal ka) corresponds to the first Late Wisconsinan ice advance across the Grand Banks and NE Newfoundland Shelf. The following three meltwater discharges (23–23.5, 23.8–24.5, and 25–27 cal ka) deposited sand turbidites and glaciogenic debris-flow deposits seaward of Trinity Trough, which was occupied by an ice stream at this time, and mud turbidites in the southern part of the basin derived from a mid-shelf ice margin on the Grand Banks. Four periods of meltwater discharge occurred during the deglaciation and are centered at 15, 18.5, 19.75, and 20.75 cal ka. The youngest is correlated to Heinrich event 1. In the literature, the 18.5 and 20.75 cal ka events have been recorded in multiple glacial settings in the North Atlantic, and therefore, are interpreted as large-scale events of meltwater discharge and iceberg calving, but in Orphan Basin the 19.75 cal ka event is also of similar scale.

Spatio-temporal variation of stable isotopes of river waters, water source identification and water security in the Heishui Valley (China) during the dry-season

Spatial variations of delta D and delta O-18 among seven tributaries and their water sources were investigated in the Heishui Valley of the Yangtze River, China during the dry-season in 2004. A one-way ANOVA (analysis of variation) test showed that both delta D (p < 0.01) and delta O-18 (p = 0.045) spatially varied among the seven tributaries. The plot of delta O-18 versus delta D for the river water collected at different locations showed that isotopic fractionation occurred during the snow and glacial melting process. The depleted delta O-18 and delta D in the tributary waters distributed above the local meteoric water line (LMWL) suggested that the glacial and early snowpack meltwater largely recharged these streams during the early spring. The meltwater was isotopically distinguishable from the precipitation and river water, which had been evaporated during warmer and drier times. If glaciers and snow accumulation diminish with future climate warming, the recharge of these tributaries' baseflow will decline and the security of the water resource in this watershed will be threatened.

Geomorphology of the Ammassalik Island, SE Greenland

Geografisk Tidsskrift, Danish Journal of Geography 108(1):5–20, 2008 Ammassalik Island is located on the elevated, passive continental margin of SE Greenland. The island itself is dominated by high ground, presumably representing part of an upwarped zone along the continental margin, separated from an adjacent narrow coastal plain. Most of the present relief must have formed during the Palaeocene and Eocene, or later, during the Neogene. During the Quaternary the area was covered by the Greenland Ice Sheet, with the exception of a few nunataqs located at the junction of the elevated bedrock plateau and the escarpment. The geomorphological evolution during the Holocene has been characterised by both glacial and periglacial processes, intensifying during the late Holocene. Especially the Little Ice Age period (c. 1200–1900 AD) appears to have been a period of enhanced geomorphological activity, mainly controlled by growing glaciers and increasing activity of periglacial processes and aggrading permafrost. Following the end of the Little Ice Age, the 20th century have seen a net development towards warmer climate with retreating glaciers and presumably also in the intensity degrading of periglacial processes and of permafrost.

Antarctic Sedimentary Basins: Key to understanding glacial processes workshop to establish an integrated seismic stratigraphy for the Ross Sea, Antarctica, Trieste, Italy, 18–20 June 2007

The Cenozoic history of the Antarctic is recorded largely in the sedimentary basins of the Antarctic continental shelf. The seismic data across these basins are particularly important in defining the development of the cryosphere over the past 35 million years, as direct sampling of the sediments is limited to cores from only a few drill holes. The geometry and character of the seismic stratigraphy are used to infer glacial processes and the age of these events. In order to have a consistent circum‐Antarctic interpretation of past glacial and tectonic events, a consistent seismic stratigraphy is needed.

Progress towards robotic in-situ dating of martian sediments using optically stimulated luminescence

Recent exploratory efforts to reveal the evolution and the climatic history of Mars have shown that the planet is still active. The surface of Mars has been, and continues to be, shaped by fluvial, eolian and glacial processes. The timeframe of these events is, however, poorly established. We describe efforts and challenges to adapt optically stimulated luminescence (OSL) dating for robotic in-situ dating of martian sediments. Mineral mixtures were devised as simulants of martian regolith. The single-aliquot regeneration (SAR) procedure was modified to enable the determination of the equivalent dose for polymineral samples. Low-temperature measurements and simulations indicate that known doses delivered at low temperatures can be effectively estimated as long as the stimulation temperature is greater than the highest temperature experienced during the initial irradiation. Bleaching experiments with a solar simulator suggest efficient zeroing of the OSL signal for solar-exposed sediments on Mars. Irradiations with proton and heavy-charged particles show a lower efficiency in luminescence production than that found for beta and gamma radiation.

Changes in ice‐margin processes and sediment routing during ice‐sheet advance across a marginal moraine

.Advance of part of the margin of the Greenland ice sheet across a proglacial moraine ridge between 1968 and 2002 caused progressive changes in moraine morphology, basal ice formation, debris release, ice‐marginal sediment storage, and sediment transfer to the distal proglacial zone. When the ice margin is behind the moraine, most of the sediment released from the glacier is stored close to the ice margin. As the margin advances across the moraine the potential for ice‐proximal sediment storage decreases and distal sediment flux is augmented by reactivation of moraine sediment. For six stages of advance associated with distinctive glacial and sedimentary processes we describe the ice margin, the debris‐rich basal ice, debris release from the glacier, sediment routing into the proglacial zone, and geomorphic processes on the moraine. The overtopping of a moraine ridge is a significant glaciological, geomorphological and sedimentological threshold in glacier advance, likely to cause a distinctive pulse in distal sediment accumulation rates that should be taken into account when glacial sediments are interpreted to reconstruct glacier fluctuations.

Formação ferrífera associada à sedimentação glaciogênica da Formação Puga (Marinoano) na Serra da Bodoquena, MS

Iron formation associated with diamictite interpreted as belonging to the Puga Formation (Marinoan) is reported here in a different context from the already known deposits of the Jacadigo Group, at the Urucum´s Massif. The iron formation occurs as a bed about 2 m thick, oriented NS and dipping 45o to East, confined in a massive foliated diamictite with ferruginous matrix presenting low metamorphism. It’s composed of centimetric hematite and magnetite layers alternated with submilimetric layers of silica, sometimes stretched due to the tectonic deformation of the Paraguay Mobile Belt. Fe 2 O 3 vary from 75% in the borders, to 52% in the center of the body. The iron concentration in the borders is due to the remobilization of silica to the center of the body, probably because of the tectonic events. Chemical analyses show that Al 2 O 3 concentrations are high (2,89 – 3,45%), and the strong linear correlation with TiO 2 and Zr indicate terrigenous contribution during chemical deposition. Isolated blocks of granite occur within the BIF, but tectonic overprinting makes it difficult to have a clear observation of the relationship between the clasts and original lamination. Despite the Puga Formation has its origin related to glaciogenic events, there are no clear evidence to link this iron formation origin to the glacial processes.

Climatic control on river discharge simulations, Zackenberg River drainage basin, northeast Greenland

AbstractA spatially distributed, physically based, hydrologic modeling system (MIKE SHE) was applied to quantify intra‐ and inter‐annual discharge from the snow and glacierized Zackenberg River drainage basin (512 km2; 20% glacier cover) in northeast Greenland. Evolution of snow accumulation, distribution by wind‐blown snow, blowing‐snow sublimation, and snow and ice surface melt were simulated by a spatially distributed, physically based, snow‐evolution modelling system (SnowModel) and used as input to MIKE SHE. Discharge simulations were performed for three periods 1997–2001 (calibration period), 2001–2005 (validation period), and 2071–2100 (scenario period). The combination of SnowModel and MIKE SHE shows promising results; the timing and magnitude of simulated discharge were generally in accordance with observations (R2 = 0·58); however, discrepancies between simulated and observed discharge hydrographs do occur (maximum daily difference up to 44·6 m3 s−1 and up to 9% difference between observed and simulated cumulative discharge). The model does not perform well when a sudden outburst of glacial dammed water occurs, like the 2005 extreme flood event. The modelling study showed that soil processes related to yearly change in active layer depth and glacial processes (such as changes in yearly glacier area, seasonal changes in the internal glacier drainage system, and the sudden release of glacial bulk water storage) need to be determined, for example, from field studies and incorporated in the models before basin runoff can be quantified more precisely. The SnowModel and MIKE SHE model only include first‐order effects of climate change. For the period 2071–2100, future IPCC A2 and B2 climate scenarios based on the HIRHAM regional climate model and HadCM3 atmosphere–ocean general circulation model simulations indicated a mean annual Zackenberg runoff about 1·5 orders of magnitude greater (around 650 mmWE year−1) than from today 1997–2005 (around 430 mmWE year−1), mainly based on changes in negative glacier net mass balance. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Landscape evolution degrades the geologic signature of past glaciations

Glaciers on land leave behind characteristic landforms and bedrock topography. The spatial extent of this signature and dating of the erosional and depositional features has led to a good understanding of temporal and spatial shifts of past glaciers and climate. At best the landscape contains considerable information on past glacial processes in the form of moraines and other depositional landforms. However, evidence suggests that all unconsolidated landforms degrade, manifested in the general degradation and smoothing of the topography over time. To determine the relative amount and pattern of degradation on glacial moraines we use a well-documented moraine degradation model that uses both local slope and a proportionality constant to determine the diamicton transport rate. This formulation results in diffusion type topographic smearing and smoothing of the initially angular topographic features. More specifically, diamicton is eroded at the crest of a moraine, transported downhill, and deposited on the gentler lower flank. Collectively this produces moraine cross-profiles that closely resemble observations in the field. By assuming an initial constant boulder frequency per unit volume of the diamicton, the model tracks the surface lowering and the related exhumation of boulders to the moraine surface. This produces a tightly constrained set of testable predictions: (1) modelled moraine cross-profile; (2) modelled spatial pattern of surface boulders (no boulders on the lower flank); and (3) relative frequency of surface boulders (smallest frequency of surface boulders at the inflection point, highest frequency at the crest). These characteristics were measured in the field of alpine, tropical, and Antarctic moraines. The correspondence between model predictions and field data is remarkably good, and strongly supports our understanding of the time dependent evolution of glacial landscapes. These results highlight the evolving nature of glacial landforms and indicate the complete removal of original moraine surfaces and postglacial emergence of spatial pattern in boulder frequency.

Glacial landscape evolution — Implications for glacial processes, patterns and reconstructions

This special issue presents a collection of papers that address a wide range of important challenges and exciting advances in the field of glacial landscape evolution. Primarily, these papers reflect persistent uncertainty that surrounds the mechanisms and timescales of glacial landscape evolution. For example, estimates of the duration of glacial occupancy required for the evolution of characteristic glacial valley forms from previously fluvial landscapes range from 100 kyrs for landscapes beneath large ice sheets (Jamieson et al.) to ~ 400–600 kyrs for glaciated alpine terrains (Brook et al.). Further, the mechanisms of glacial erosion are debated through analyses of the importance of ice thickness (Brocklehurst et al.; van der Beek and Bourbon), ice surface steepness (Vieira) and, in the case of large ice sheets, the co-evolution of ice sheet thermal regime, dynamics, and subglacial topography (Kleman et al.; Swift et al.). Debate concerning the potential climatic impacts of landscape evolution in alpine terrains is represented by van der Beek and Bourbon, who infer a significant increase in relief as a direct result of glacial erosion, and by Brocklehurst et al. and Heimsath and McGlynn, who demonstrate respectively that glacial relief production can be surprisingly modest and that rates of glacial erosion may be lower than those for fluvial incision. Further confirmation that valleys beneath large ice sheets evolve through selective linear erosion comes from studies that have combined geomorphological evidence with cosmogenic nuclide (Briner et al.) and apatite (U–Th)/He thermochronometry (Swift et al.), and the resulting style of landscape evolution is demonstrated by the antiquity of fjords in East Greenland (Swift et al.) and of deep erosion zones and thick drift covered zones in Fennoscandia (Kleman et al.), although the location of areal scouring zones may be subject to major alteration during single glacial events (Kleman et al.). Another set of papers shows that analyses of glacial lineation systems continue to provide important data on the dynamics of glacial landscape evolution, whether the lineations are formed underneath ice streams (Bradwell et al.; Andreassen et al.) or not (Jansson and Glasser), and whether they indicate intricate patterns of landscape modification (Andreassen et al.) or preservation (Jansson and Glasser). The final three papers address rarely-reported issues relating to landscapes of glacial deposition, including moraine degradation (Putkonen et al.), proglacial hydrogeology (Robinson et al.), and the evolution of hummocky-till topography (Clayton et al.).

Triggering of the Hinlopen/Yermak Megaslide in relation to paleoceanography and climate history of the continental margin north of Spitsbergen

On the basis of the detailed sedimentological record of the key‐core PS66/309‐1 and a review of open literature, we present an assessment of the paleoenvironmental conditions as well as trigger mechanism of the Hinlopen/Yermak Megaslide north of Spitsbergen. The Svalbard archipelago is characterized by strong inflow of Atlantic water accompanied by rapidly falling sea level, rapidly growing Svalbard‐Barents Sea‐Ice Sheet, and associated increasing glaciotectonic activity during the time window around 30 calendar kyr B. P. of this catastrophic failure event. Thus the potential trigger mechanisms include sediment buoyancy and excess pore pressure, hydrate stability, and tectonic/glaciotectonic processes. While the common scenarios seem to fail to explain this unique submarine megaslide, we focus on glacial processes and their consequences for the regional tectonic framework. We conclude that the Hinlopen/Yermak Megaslide has been the consequence of the rapid onset of Late Weichselian glaciation resulting in a drastic sea level drop, asymmetrical ice loading, and a forebulge development leading to enhanced tectonic movements along the Hinlopen fault zone. As the final trigger we assume a strong earthquake positioned below or close to the SE Sophia Basin.

Coupling glacial erosion and tectonics at active orogens: A numerical modeling study

Climate change indirectly alters the distribution of tectonic uplift at active orogens by modifying the action of surface processes, which in turn alters mountain topography. The impact of alpine glaciation on tectonic activity is explored here. The predictions of previous analytical, critical wedge models are compared with the output of a numerical model that explicitly couples rock uplift produced by convergence with surface erosion. Glacial and fluvial and erosive processes are calculated over a two‐dimensional grid, which uses an ice evolution model to calculate the rate of glacial erosion due to ice sliding. Tectonic uplift is determined by a two‐dimensional finite element convergence model. The simulations performed support the predictions of previous one‐dimensional analytical modeling of fluvially dominated orogens: Increasing precipitation decreases orogen width by the one quarter power. The simulations show that glacially dominated landscapes have similar dependencies. The total glacial erosion yield is determined to be proportional to the glacial coverage, sublinearly dependent on the precipitation rate, and linearly dependent on the glacial erosion constant that relates erosion with sliding speed. Climate also determines the distribution of tectonic uplift in the model. If the equilibrium line altitude (ELA) is high and glacial processes are limited to peak regions, the center of the mountain range experiences the highest rate of rock uplift. Extensive glaciation increases rock uplift rates on the flanks of the range. The style of glacial erosion is also important: A simple glacial buzzsaw does not create the same tectonic response as models that physically simulate glacial erosion. The simulations support the idea that a climate cooling of the magnitude recorded in the late Cenozoic has the potential to more than double the rate of rock uplift in appropriate orogens. The implications of the model are discussed for observations from the Olympic Mountains of Washington State, the Southern Alps of New Zealand, the Alaskan coastal range, and the southern Andes.

Hemispheres Apart: The Crustal Dichotomy on Mars

The hemispheric dichotomy is a fundamental feature of Mars, expressed by a physiographic and geologic divide between the heavily cratered southern highlands and the relatively smooth plains of the northern lowlands. The origin of the dichotomy, which may have set the course for most of the subsequent geologic evolution of Mars, remains unclear. Internally driven models for the dichotomy form the lowlands by mantle convection, plate tectonics, or early mantle overturn. Externally driven models invoke one giant impact or multiple impacts. Areal densities of buried basins, expressed by quasi-circular depressions and subsurface echoes in radar sounding data, suggest that the dichotomy formed early in the geologic evolution of Mars. Tectonic features along the dichotomy boundary suggest late-stage modification by flexure or relaxation of the highlands after volcanic resurfacing of the northern lowlands. Subsequent deposition and erosion by fluvial, aeolian, and glacial processes shaped the present-day dichotomy boundary.

Seismicity of the Bering Glacier region and its relation to tectonic and glacial processes

We relocated over 1000 earthquakes of magnitude > 0.1 occurring between 1973 and 2001 in the Bering Glacier region of southern Alaska. We used first-motion data from these events to determine focal mechanisms and directly invert for stress orientations. Our results indicate that much of the seismicity in the region is occurring within the North American plate in a zone where an inferred structure, which lies beneath Bering Glacier, intersects the Chugach-St. Elias fault system. Stress-field analysis indicates that the events in the Bering Glacier surge reservoir region are likely occurring on northeast-trending thrust faults, consistent with previous modeling that suggested thrust faulting would be enhanced in regions of ice draw down. We also observe a stress field compatible with either high-angle normal or reverse faulting in regions located northwest of the Bering Glacier. This may indicate localized complexities in interactions between the Bering Glacier structure and the Chugach-St. Elias fault system.

Online Versus Hardcopy Textbooks

Seven years (2000–2006) of analysis of 1751 introductory lab science students in 10 separate semesters at Arizona State University reveals no statistically significant differences in class performance between online (81.2 ± 11.0) and hardcopy (80.8 ± 10.8) textbook users. In a required physical geography lab science class, students were given the option of using either an online ( n = 760) or a hardcopy ( n = 991) text to reinforce learning such topics as Wien's law, invading species, dissolution of minerals, Chezy-Manning equation, and glacial processes. By any measure, the hardcopy texts were more sophisticated than the online alternative, even though the basic information remained similar. Yet, even after disaggregating data into different semesters, texts, disciplines, class, GPA, age, ethnicity, and whether the student is a first-generation college student, no statistically significant differences emerged. Given the importance of required lab courses in shaping opinions of college-educated citizens about the importance of science, and given the growing resentment expressed by students over increasingly high-priced textbooks, similar studies in other general education lab science disciplines would seem justified.

Discussion of “Geology and diamond distribution of the 140/141 kimberlite, Fort à la Corne, central Saskatchewan, Canada”, by A. Berryman, B.H. Scott-Smith and B.C. Jellicoe (Lithos v. 76, p. 99–114)

A wide variety of geological data and geological observations by numerous geoscientists do not support a two-stage crater excavation and in-fill model, or a champagne glass-shaped geometry for the 169 or 140/141 kimberlite bodies in the Fort à la Corne kimberlite field, Saskatchewan as described by Berryman, A., Scott Smith, B.H., Jellicoe, B., (2004). Rather, these kimberlite bodies are best described as polygenetic kimberlite tephra cones and tuff rings with associated feeder vents of variable geometry as shown by previous workers for the 169 kimberlite, the 140/141 kimberlite and the Star kimberlite. The domal tephra cone geometry is preserved due to burial by conformable Cretaceous marine mudstones and siltstones and is not an artifact of Quaternary glacial processes.