Search

Our understanding of the response of the Antarctic ice sheet to climate and ocean changes requires the improvement of current ice-atmosphere-ocean models and the accurate determination of boundary conditions such as ice thickness and extent at key time intervals, so that satellite gravity observations and isostatic models can be adjusted. However, large portions of the Antarctic margin remain understudied or lack suitable data. One key area where data are lacking, is the Sabrina Coast portion of the East Antarctic Ice Sheet (EAIS) margin where the Totten Glacier, which has the largest ice discharge in East Antarctica, is accelerating, thinning and loosing mass at high rates. In this work, we present the results of the first geological and geophysical marine survey to the continental shelf offshore of the Dalton Ice Tongue and Moscow University ice shelf, east of the Totten Glacier. The data presented include multibeam swath bathymetry and multichannel seismic, focusing on the sea floor morphology and sedimentary section above a regional angular unconformity separating pre- and post-Miocene glacial strata. Sea floor scouring and iceberg keel marks on the outer shelf, associated with gullies on the upper slope indicate that ice expanded in the past and grounded ~5 km from the shelf edge at ~450–500 mbsl, extending ~155 km north of the current Moscow University Ice Shelf. A nearly 1000 m deep area in the inner-middle shelf, oriented NW with paleo-ice flow direction indicated by mega scale glacial lineations (MSGL) and drumlins, is interpreted as a cross shelf glacial trough. A series of geomorphic associations on the north-eastern side of the glacial trough includes glacial lobes, grounding zone wedges (GZW), glacial lineations and transverse ridges, which indicates slower ice, grounding line stabilization and collapse. These geomorphic associations are organized in 4 four sets representing different past ice-flow configurations reflecting changes in ice flow direction, grounding line position, location of fast and slow ice areas, and retreat pattern. Some of the geomorphic features identified are compatible with the presence of an organized subglacial drainage, and others are with rapid grounding line collapse. A well-preserved series of GZWs occurring at different water depths implies they were formed during different glacial stages or cycles. The inferred diminishing ice thickness for consecutives GZWs indicates that the margin of the Antarctic ice sheet evolved to a less extensive coverage of the continental shelf through successive glacial stages or cycles. The identification of different ice flow configurations, evidence of subglacial water and past ice margin collapse indicates a dynamic ice sheet margin with varying glacial conditions and retreat modes. We observe that some of the described morphological associations are similar to those found in the Amundsen sea sector of the West Antarctic Ice Sheet (WAIS) where they are associated with ice sheet and ice stream collapse. Although further studies are needed to assess the precise timing and rates of the glacial processes involved, we conclude that there is enough evidence to support the hypothesis that the EAIS margin can behave as dynamically as the WAIS margin, especially during glacial retreat and icesheet margin collapse.

Quaternary valley fills and landforms in the Waqia valley of the Chinese Pamir were examined using geomorphic mapping, geomorphic and sedimentological analysis of landforms and sediments, and cosmogenic 10Be surface exposure dating. Six sets of moraines (M-1 to M-6) are identified and date to the penultimate or an older glacial cycle (M-1), penultimate glacial cycle (M-2), early last glacial and probably Marine Oxygen Isotope Stage (MIS) 4 (M-3), MIS 2 (M-4), Late Glacial (M-5), and early Holocene (M-6). Younger moraines are also present, but these were not examined in detail. Alluvial fans and outwash/river terraces are present throughout the valley. Four surfaces on alluvial fans and river terraces were dated to ~ 580 ka (T-1), ~ 120 ka (T-2), ~ 100 ka (T-3), and ~ 70 ka (T-4). Large landslide and lacustrine deposits are common within the valley fills and represent periods of major slope instability and possible damming of drainages. Glacial processes dominate the western side of the valley; landsliding is the leading process on its eastern side. Defining the nature and timing of landform formation in this valley highlights the punctuated nature of landform evolution in the Himalaya and Tibet and provides a framework for considering the abundant valley fill successions elsewhere in the orogen.

Reconstruction based on the geomorphology, lateral moraine stratigraphy, and limited optical chronology indicate that the monsoon-dominated Kosa Valley experienced four glacial advances during the late glacial to late Holocene. The oldest and most extensive glaciation, which is termed as Raj Bank Stage-1 (RBS-1), is represented by the degraded moraine ridge. This glaciation remains undated; however, the chronology of outwash terrace gravel dated to 12.7 ± 1.3 ka indicates that the RBS-1 probably represents the Last Glacial Maximum (LGM). The second glacial advance (RBS-2) is preserved as a curvilinear lateral moraine and is dated to 6.1 ± 0.4 ka. The third glacial advance viz. RBS-3 is bracketed between 5.0 ± 0.5 and 4.0 ± 0.4 ka. Following this, the glacier receded in pulses that are represented by two distinct recessional moraines (RBS-3a and b). The forth glacial stage (RBS-4), which is dated between 2.2 ± 0.2 and 1.6 ± 0.2 ka, shows a pulsating recession and is represented by a prominent recessional moraine (RBS-4a). Whereas, presence of unconsolidated, poorly defined moraine mounds proximal to the glacier snout are ascribed as neoglacial advance corresponding to the Little Ice Age (LIA). With the limited chronometric data, we speculated that the glaciation was driven during the weak to moderate Indian Summer Monsoon (ISM) aided by lowered temperature. Presence of recessional moraines associated with mid-Holocene glacial phase indicate that the monsoon-dominated glaciers respond sensitively to minor (sub-millennial scale) changes in temperature and precipitation conditions. The observations are broadly in accordance with the studies carried out in other monsoon-dominated valleys in the central Himalaya, implying that in ISM dominated regions, lowered temperature seems to be the major driver of glaciations during the late glacial to late Holocene.

Fluvial, glacial, and estuarine deposits in the Delaware Valley record the response of the Delaware River to glaciation, sea-level change, and glacioisostasy during the Quaternary. Incision following an early Pleistocene glaciation created the present valley, which is inset into a Pliocene strath and fluvial plain. Middle and upper Pleistocene and Holocene deposits were laid down in this inset valley. Estuarine terraces in the lower valley and bayshore at + 20 m (probably Marine Isotope Stage [MIS] 11), + 8 m (MIS 5e), and + 3 m (MIS 5a or c), and a fluvial deposit that correlates to offshore MIS 3 marine deposits at − 20 m are at elevations consistent with glacioisostatic models. Successive incisions during lowstands in the middle and late Pleistocene lengthened, deepened, and narrowed the channel in the lower valley and shifted the channel westward in Delaware Bay. During MIS 2 glaciation, from 25 to 18 ka, the Delaware was diverted to the Hudson Shelf Valley by glacioisostatic tilting. Most glacial sediment was trapped in fluvial-lacustrine valley fills north of the terminal moraine. Incision of the valley fill was accomplished during the early stage of rebound, between 17 and 12 ka. Drainage to the Delaware shelf was restored between 15 and 13 ka as the forebulge collapsed. During incision, multiple postglacial terraces formed where the valley was perpendicular to rebound contours and so was steepened and elevated northward; and a single terrace formed where the valley paralleled the contours, and there was no differential elevation or steepening. About 65% of the original volume of MIS 2 glacial sediment remains in the main valley, and most of the eroded volume is in the channel in the lower valley beneath Holocene estuarine fill. Little glacial sediment reached the Delaware or Hudson shelf. Overbank deposition on the lower postglacial terrace and modern floodplain spans the Holocene. The volume of Holocene sediment in the estuary and bay yields a basinwide denudation rate of about 20 m/my.

The Piec Stawow Polskich-Roztoka Valley in the High Tatras (Western Carpathians) features typical alpine-type relief with a deeply incised glacial trough and large, compound trough head cirque. The prominent hypsographic maximum in the valley (1680–2000 m) along with a broad cirque bottom had provided a vast space for recording glacial and periglacial landforms, specifically the most recent Lateglacial advances. The valley has been intensively studied before in the context of glacial chronology. In this paper, we re-establish the post-Last Glacial Maximum (LGM) glacial chronology of the valley via detailed geomorphologic mapping, equilibrium line altitude (ELA) reconstruction, and Schmidt hammer (SH) dating, along with a critical review of previously published cosmogenic exposure age data ( 36 Cl) and lacustrine sediment chronology. Our results indicate that the first four of the five distinguished Lateglacial stages (Roztoka I–III, Pusta I) occurred before the Bolling/Allerod (B/A) interstadial; thus, virtually the entire valley became deglaciated in course of the Oldest Dryas cold phase. A distinct reorganization of deglacial patterns from valley-type to marginal-type occurred before B/A warming when the ELA increased above the valley hypsographic maximum concentrated at the cirque bottom elevation. It shows that noticeable deglaciation step can be caused due to topographic reason with a minimal climate forcing. This points also to an important role of glaciated valley hypsography in regulating the distribution of moraines which is rarely taken into account in paleoglaciological reconstructions. We infer that glaciers vanished in the Tatra Mountains during the B/A interstadial. Later, a renewed advance during the Younger Dryas (Pusta II) formed a nearly continuous, festoon shaped pattern of moraines and rock glaciers in close distance to cirque backwalls. Furthermore, we discus some paleoenvironmental significance of the geomorphological record in the valley, as well, the applicability of SH dating in constructing glacial chronology.

Glacial geomorphological mapping from satellite imagery and field investigations provide the basis for a reconstructionof the extent and style of glaciation of the Shaluli Shan, a mountainous area ...

article i nfo Alluvial rivers of the eastern Puget lowland, a landscape shaped by scour and fill from the Cordilleran ice sheet, continue to respond to patterns of deposition and scour by the last-glacial-age ice sheet 18,000 years after deglaciation. Topography revealed by valley cross sections created from high resolution LIDAR digital elevation models shows that rivers are aggrading in valleys eroded by subglacial runoff and degrading in valleys incised by rivers post-glaciation. Slope-area analysis of river profiles shows that profile concavity varies systematically between river segments in the two valley contexts. Concavity indices (θ) in mountain headwaters (0.3b θb0.9) compare to those of many world rivers (0.2b θb1.0), but in the lowlands these indices differ between valleys created by subglacial fluvial erosion (5b θb45) and post-glacially incised river valleys that grade to base levels set by these relict glacial valleys or by post-glacial sea levels (1b θb7). Dramatic differences in river pattern, landforms, and dynamics occur in valleys having contrasting (aggrading vs. degrading) and incomplete responses to Pleistocene glaciation, creating discrete valley-scale hetero- geneities in fluvial process domains along and between rivers. These results point to the importance of valley- scale organization of alluvial process domains along and between rivers having profiles remaining in disequilibrium from Pleistocene glaciation. They also point to the potential usefulness of slope-area analysis of longitudinal profiles in distinguishing among different river valley process domains in lowland alluvial landscapes.

In almost all former and presently glaciated areas of the world, glaciers have modified or even transformed pre-glacial terrain during the many cold stages of the Pleistocene. In consequence, the early stages in the development of glacial landscapes have been overprinted or erased by later phases of erosion. The Sudetes in central Europe provide exceptional opportunities to examine the inception of glacial erosion. Evidence of a long geomorphic evolution before glaciation, with the development of etch surfaces, deep weathering covers and the preservation of Neogene kaolinitic sediments, provides a direct analogue to other lowland crystalline terrains as existed immediately prior to Pleistocene glaciation. Large granite intrusions exist in the Sudetes and its Foreland that support hills that range in size from small tors to large domes. These terrains experienced only thin ice cover for short periods when the Scandinavian ice sheet reached its Pleistocene maximum limits in Marine Isotope Stage (MIS) 12 (Elsterian) at 440–430 ka and MIS 8 (Early Saalian) at 250–240 ka. In each of four study areas beyond, at and within the limits of glaciation we have mapped Glacial Erosion Indicators, glacial landform assemblages that indicate progressive glacial modification of the pre-glacial granite terrain. We find that glacial erosion increases with distance from the ice margin, due to greater ice thickness and longer ice cover, but has had only limited impact. On hills, regolith was stripped by moving ice, tors were demolished, and blocks were entrained. However, indicators of more advanced glacial erosion, such as lee-side cliffs and glacial streamlining, are absent, even from granite domes that lay beneath ~ 500 m of ice. The survival of tors beneath ice cover and the removal of tor superstructure by glacial erosion are confirmed. The presence of glacially-modified tors in areas covered only by Elsterian ice implies that the tors existed before 440 ka. Moreover, the contrast between blockfield-covered slopes found above Elsterian and Saalian glacial trimlines on summits of granite, gabbro and basalt hills in the Sudetic Foreland and glacially-stripped surfaces at lower elevations implies only limited regeneration of blockfields since 430 and 240 ka. The first stages of roche moutonnee formation are recognised in the exhumation of tor stumps but development of lee-side steps remains very limited. Granite domes retain a pre-glacial morphology and local examples of hill asymmetry are determined by structural, rather than glaciological controls. Development of roches moutonnees and asymmetric and streamlined hills by glacial erosion has not occurred in the Sudetes despite the passage of largely warm-based ice sheets 80–500 m thick that persisted for 5–20 ka.

Low-order alpine glacial valleys on Earth commonly have a characteristic spacing of 1–3 km. Here we develop analytic and numerical solutions of a coupled numerical model for alpine glacial flow and subglacial bedrock erosion to quantitatively determine the controls on glacial valley spacing assuming an initially-undissected landscape, an initially-fluvially-dissected landscape, and an initially-cratered landscape. The characteristic spacing of glacial valleys produced by the model is controlled by a competition between the thickening of ice in incipient glacial valleys, which acts to enhance flow and valley deepening, and viscous/sidewall drag, which acts to limit flow and deepening. The glacial valley spacing that represents the best compromise between these two competing effects is found to be a function of valley slope, the threshold basal shear stress for ice motion, the effective ice viscosity, a bed-friction parameter, and gravity. This model framework provides the preliminary basis for understanding the relative spacing of glacial valleys on Earth and Mars. On Mars, montane glacial valleys have widths and spacings that are approximately 10–20 times larger than those on Earth. Model results suggest that this difference is predominantly a consequence of lower bed slopes and larger temperature-controlled ice viscosities of glacial ice on Mars compared to Earth.

This paper presents an improved geomorphological methodology that uses remotely-sensed data, a Geographical Information System and a brief field campaign to allow rapid, yet, precise mapping as well as interpretation and analysis of glacial earth surface morphology in high mountain areas. The study area consists of the Quaternary-glaciated part of the Coumelade valley (Canigou massif, eastern Pyrenees, France), which ranges between 1450 and 2731 m a.s.l. A topographical-map-derived Digital Elevation Model was used for analyzing glacial landforms by extracting the slope gradient, valley profiles and the slope aspect. The results were gradually refined from the interpretations of aerial photograph and the field investigation. Glacial landforms are present above 1500 m a.s.l. and include glacial and nivation cirques, cirque and latero–frontal moraines (7.7 × 106 m³) and micro-scale landforms such as chattermarks, crescent grooves and polished surfaces. The geomorphological investigation reveals that the Quaternary glaciation of the Coumelade valley remained limited, resulting in a low denudation rate of 0.011 mm yr− 1 over the last glacial cycle.

Jansson and Glasser (Jansson, K.N., Glasser, N.F., 2008. Modification of peripheral mountain ranges by former ice sheets: the Brecon Beacons, southern UK. Geomorphology 97, 178–189.) have recently provided unconventional interpretations of selected glacial erosional and depositional landforms in the Brecon Beacons, UK, based on remotely sensed imagery. These new interpretations contradict well-established and reliable evidence for the origins and ages of certain glacial landforms of this upland area and elsewhere. They suggest that during a post-Last Glacial Maximum (LGM) ice-sheet event ice flowed up supposed, essentially “fluvial” valleys producing “glacial lineations” and depositing marginal moraines at the valley heads and on cirque floors. We argue that their interpretations of some key landforms are incorrect and that they have ignored much of the previous dating and field geomorphological evidence. Sedimentary and morphological evidence (e.g., lack of erratic content; convex planform with respect to the headwall; relatively large height range of moraines; and close association with headwall extent, height, and steepness) all indicate that higher level cirque-floor and valley-head moraines in the Brecon Beacons (> c. 400 m) were formed by cirque glaciers. Available dating evidence indicates a Younger Dryas age. We demonstrate that the supposed “fluvial” valleys, comprising trough heads with steep headwalls, have more nearly parabolic than V-shaped cross profiles indicating substantial glacial modification. Field evidence shows that proposed key exemplar post-LGM glacial lineations are in fact debris flow deposits. We conclude that whilst the adoption of a macroscale approach can shed new light on large-scale, ice-sheet movements, this approach should not be undertaken without consideration of the associated field evidence.

The Shaluli Mountains, a tectonically controlled mountain range between the Jinsha and Yalong River Rifts, are located in southeastern Tibetan Plateau. In the central Shaluli Mountains, an ice cap of ~ 3600 km2 once developed on the Haizi Shan. Abundant glacial landforms are present on the Haizi Shan and in the surrounding river valleys. Together with the outwash terraces in the Yazheku River, the northeastern part of the Haizi Shan provides an ideal site to examine the Quaternary glacial history of the region. Sedimentological and morphostratigraphical analysis, field mapping, and dating by electron spin resonance (ESR) define at least seven major glacier advances in the Haizi Shan area. Six major glacier advances likely occurred during marine oxygen isotope stage (MIS)-16, MIS-14/12, MIS-6, MIS-3, early MIS-2, and the global Last Glacial Maximum. These can be defined on the basis of ESR dating and stratigraphical analysis of the glacial landforms in front of the Kuzhaori glacial trough on the southern slope of the Haizi Shan. The outwash terraces in the Yazheku River also record four major glacier advances, which occurred during MIS-16, MIS-12, MIS-6, and MIS-2. In addition, the moraines preserved on the southwestern part of the Haizi Shan suggest that a glacial advance likely occurring during the Lateglacial. The extent of glaciation on the Haizi Shan decreased with time.

In southern South America, the maximum areal extent of ice during the Quaternary Period, the Greatest Patagonian Glaciation (GPG, [Mercer, J.H., 1983. Cenozoic glaciation in the southern hemisphere. Annual Reviews of Earth and Planetary Science 11, 99-132.]), occurred at 1.1 Ma and subsequent glaciations were overall less extensive. The GPG preceded global minimum temperatures and maximal volume of ice, which occurred in the last ~ 800 kyr, as recorded in the marine δO record. Significant modification of the drainage morphology of the southern Andes from a non-glaciated to glaciated landscape occurred throughout the Quaternary Period. We infer a non-climatic relationship between glacial modification of the mountains and the decreasing extent of ice and we discuss processes of landscape development that could have caused the trend. Specifically, these include modification of valleys, such as development from a V- to a U-shape, and lowering of mass-accumulation areas. Such changes would strongly affect glacial dynamics, the mass balance profile and mass-flux during succeeding glaciations, especially for low-gradient outlet glaciers occupying low areas. Other areas around Earth (at least where ice has been warm-based) also may exhibit a non-random trend of decreasing extent of ice with time, ultimately because of glacial erosion in the Quaternary Period.

The Ateaoyinake River originates on the southern slope of the Tumur Peak, the largest center of modern glaciation in the central Tianshan Mountains in China. Six sets of moraines and associated glacial sediments are well-preserved in the Ateaoyinake River drainage, recording a complex history of Quaternary glacial cycles and landscape evolution. Dating the landforms allow the temporal and spatial shifts of past cryosphere and climate to be determined. Dating of the tills and outwashes was undertaken with electron spin resonance (ESR) and optically stimulated luminescence (OSL). Two OSL ages date outwash and till to 7.3 ±0.8 ka and 12.3 ± 1.2 ka, respectively. The ESR ages date six sets of moraines to 3.4 ka, 14–27 ka, 40–54 ka, 55–62 ka, 134.4 ± 12.6 ka and 219.7 ± 20.5 ka, 440.6 ± 41.7 ka. If these are correct ages of deposition, they suggest that glaciers advanced during the Neoglacial and during marine oxygen isotope stages (MIS) 2, 3b, 4, 6 and 12. The MIS 3b moraine was created by a glacier nearly as large as or possibly larger than those of the “global” Last Glacial Maximum of MIS 2. The oldest till belongs to the “Qingshantou Glacial Stage”. Its single age is consistent with two published ESR ages (459.7 ± 46 and 471.1 ka) from the Gaowangfeng till near the headwaters of the Urumqi River in the eastern Tianshan Mountains. These dates suggest that the central and the eastern segments of the Tianshan Mountains were high enough to be glaciated by MIS 12. The geochronology of the glacial landforms in this valley is the first step towards understanding glacial and landscape evolution in this region. Furthermore, this geochronology and previously published geochronology near the headwaters of the Urumqi River provide a temporal framework for examining the rates of landscape evolution in the glaciated regions of the Tianshan Mountains.

A key problem in understanding valley evolution in alpine landscapes has been the lack of an independent timescale against which to measure morphological change. Here, we outline that by using space as a proxy for time, the role of glaciation in producing ‘classic’ U-shaped valleys can be quantified. The Two Thumb Range in New Zealand's central Southern Alps is undergoing rapid tectonic transport and uplift as it is advected towards the Alpine Fault. Repeated cycles of glacial erosion during the Quaternary have fashioned an alpine landscape in the north of the range, close to the Main Divide and Alpine Fault, while valleys in the less glaciated south of the range have rounded divides and convex fluvial cross-profiles. Using known rates of tectonic transport and uplift of the Southern Alps, coupled with an offshore oxygen isotope (δ18O) record from the Chatham Rise and glacio-geological reconstructions, time constraints can be applied to the erosional development of valleys. It is possible to estimate the duration of glacial occupancy of valleys in the Two Thumb Range, and the pattern is one of very limited glaciation of the southern valleys, with glacial occupancy increasing northwards. The key trend identifiable is that valley cross-profiles become U-shaped with c. 400–600 kyr of glacial occupancy. Other models have shown a “flattening” of valley long-profiles with increased glaciation, implying glaciers erode larger volumes of rock from mountains than rivers. From a cross-profile perspective, the simple change in geometry from V- to U-shape concurs with these models. Indeed, the transition from V- to U-shape with increasing relief and glaciation indicates glaciers may erode greater volumes of rock from mountain belts than rivers.

The relative rates of erosion by rivers and glaciers, and the topographic effects of these two different styles of erosion, remain outstanding problems in geomorphology. We use a quantitative description of local fluvial landscapes to estimate how glaciated landscapes might look now had glaciers not developed. This indicates the landscape modification attributable to glacial erosion. We present examples from the Sierra Nevada, California and the Sangre de Cristo Range, Colorado. In smaller drainage basins, glacial modification is focussed above the mean Quaternary equilibrium line altitude (ELA), where both ridgelines and valley floors have been lowered as a consequence of glaciation. At lower elevations, small glaciers have apparently widened valleys without incising the valley floor beyond what a river would have. This may reflect the short residence time of the glaciers at their full extent, or differences in the subglacial drainage network between the glacier margins and the thalweg. In larger drainage basins, the pattern of glacial erosion is dramatically different. Here, the glaciers have modified longitudinal profiles, as well as valley cross sections, far below the mean Quaternary ELA. Possible causes of this difference in the larger basins include the larger accumulation area, greater shading of the valley floor, longer residence times for ice at its full extent, and the influence of the shallower valley slope prior to glaciation on the subsequent glacier and subglacial drainage conditions.

The Parkajoki area in northeastern Sweden is situated near the central area of Fennoscandian glaciation. Despite its location, the area is dominated by landforms induced by subaerial weathering and erosion processes, such as well-developed tors and associated saprolites, boulder fields, and boulder depressions. The glacial geomorphology is dominated by lateral and proglacial meltwater channels. Subglacial imprints indicative of thawed-bed conditions and reshaping by glacier sliding (e.g., fluting, drumlins, striae) are lacking. Hence, most of the landscape still exhibits a preglacial appearance. Because of its location, near the central area of glaciation, we attribute preservation to frozen-bed conditions of overriding ice sheets. The widespread distribution of well-developed tors and boulder fields, and the degree of chemical weathering of the bedrock, indicate that the area has been protected from glacial erosion during all glacial cycles since ice sheet initiation in the late Cenozoic. Unlike most other areas with tors in glaciated regions, the Parkajoki area is uniquely situated in the lowlands at 150–400 m.a.s.l. Moreover, this relict landscape is surrounded by glacial landscapes (including drumlins, ribbed moraine, and eskers) of varying age and at similar elevation. Hence, topographical reasons for this area being persistently cold-based cannot be invoked. By inference, we conclude that strain heat release never managed to cancel the initial subglacial permafrost conditions. We attribute this to divergent ice flow towards the convex outline of the ice sheet margin during deglaciations and to the relative roughness of the area compared to its surroundings. The implication is that to explain preservation throughout the Quaternary, all large-scale glaciations must have had a similar evolution concerning ice sheet configuration and internal dynamics as the last glaciation for which good constraints on evolution and outline are available.

We present a detailed map of the distribution of preglacial surface remnants in the Kebnekaise region of northwestern Sweden. In this mountain area we discern four important large-scale geomorphological units, each representing a specific set of erosional agents and formative conditions. These are: (i) intact preglacial surface remnants, characterized by gentle slopes, round summits, wide shallow valleys, and an absence of rock basins; (ii) preglacial surface remnants showing signs of minor glacial erosion and deposition; (iii) glacially scoured surfaces, including glacial troughs; (iv) deep fluvial valleys cut into the preglacial surface. The pattern of glacial erosion is explained as the result of three specific modes of glaciation known to have existed during the last 120,000 years, and inferred to have repeatedly prevailed during the last 2.75 million years: cirque glaciation, mountain ice sheets, and Fennoscandian ice sheets. A deep-ocean oxygen-isotope record of foraminifera from the North Atlantic (DSDP 607) was used to infer the temporal extent of these modes of glaciation during the last 2.75 million years. We interpret the preglacial landscape preservation and the pattern of glacial erosion in terms of the configuration, the basal thermal regime, and the duration of such glaciation events. The average subglacial thermal regime of both ice sheet types was frozen on the uplands and melting in the main valleys, where outlet glaciers and ice-streams formed. The pre-glacial landscape is best preserved at intermediate elevations, low enough not to have been covered by cirque glaciers, and apparently high enough not to have experienced melted-bed conditions and subglacial erosion during ice sheet overriding events. In a narrow high-relief zone along the elevation axis, interglacial fluvial erosion was morphologically important. The absence of glacial erosion on uplands in this zone allowed fluvial erosion to commence on the same locations during each ice-free interval. In contrast, no persistent fluvial valley pattern could develop in zones subjected to repeated glacial scouring and hence, derangement of fluvial patterns.

Deep canyon erosion and diversion of more than 300 km 2 of the former upper Bear River is documented with stratigraphic and morphologic evidence. Stratigraphic relationships constrain canyon incision to no older than late Miocene in age. A hypothesis is advanced that channel diversion was caused by ice spilling over a divide between the Bear and South Yuba drainages leading to development of glacial diffluence and deep incision. The local glacial stratigraphy is mapped based on lateral moraines, erratics, and striae which indicate that at least two and probably three glacial advances occupied both South Yuba and Bear valleys. Stratigraphic relationships constrain most valley incision to before the last major glacial stage and probably by the end of an earlier, larger glacial advance. Morphologic evidence supports a hypothesis of dominantly sub-glacial erosion at an outlet glacier through the Yuba gorge where steep valley gradients, high shear stresses, and large meltwater discharges led to rapid erosion and formation of a deep V-shaped valley.

Multiple alluvial, colluvial, and eolian deposits in unglaciated northern New Jersey, and the eroded bedrock surfaces on which they rest, provide evidence of both long-term valley evolution driven by sustained eustatic baselevel lowering and short-term filling and excavation of valleys during glacial and interglacial climate cycles. The long-term changes occur over durations of 10 6 years, the short-term features evolve over durations of 10 4 to 10 5 years. Direct glacial effects, including blockage of valleys by glacial ice and sediment, and valley gradient reversals induced by crustal depression, are relatively sudden changes that account for several major Pleistocene drainage shifts. After deposition of the Beacon Hill fluvial gravel in the Late Miocene, lowering of sea level, perhaps in response to growth of the Antarctic ice sheet, led to almost complete dissection of the gravel. A suite of alluvial, colluvial, and eolian sediments was deposited in the dissected landscape. The fluvial Bridgeton Formation was deposited in the Raritan lowland, in the Amboy-Trenton lowland, and in the Delaware valley. Following southeastward diversion of the main Bridgeton river, perhaps during Late Pliocene or Early Pleistocene glaciation, northeastward drainage was established on the inactive Bridgeton fluvial plain. About 30 to 45 m of entrenchment followed, forming narrow, incised valleys within which Late Pleistocene deposits rest. This entrenchment may have occurred in response to lowered sea level caused by growth of ice sheets in the northern hemisphere. Under periglacial conditions in the Middle and Late Pleistocene, valleys were partially filled with alluvium and colluvium. During interglacials slopes were stabilized by vegetation and the alluvial and colluvial valley-fill was excavated by gullying, bank erosion, and spring sapping. During Illinoian and late Wisconsinan glaciation, the lower Raritan River was diverted when glacial deposits blocked its valley, and the Delaware River was partially diverted down the isostatically-steepened lower Millstone valley.