Landform Assemblages Research Articles

Glacial land forms indicative of a partly frozen bed

AbstractIn parts of the core area of the Fennoscandian ice sheet relict periglacial surfaces occur. The boundary between periglacial and glacial landscapes is often sharp and erosional, with fluting truncating patterned ground. The periglacial surfaces are older than the last ice sheet and are interpreted to represent patches of continuous frozen-bed conditions. A specific land-form assemblage occurs at the edges of such patches. On the basis of three type localities along the eastern rim of the Scandinavian mountains, four thermal boundary land forms, characteristic of the frozen-patch environment, are defined. Stoss-side moraines and transverse till scarps, not previously described, are interpreted to have formed in detachment zones where soil frozen to the glacier overlies thawed soil. The detachment zones are located where subglacial warming raises the phase-change surface (water/ice) until it intersects the soil layer up-and down-glacier from residual frozen-bed patches. The up-glacier ends of frozen-bed patches are located on topographic highs, but down-glacier the location of lateral sliding boundaries is occasionally independent of topography. The identification of relict surfaces and thermal boundary forms can improve paleo-ice-sheet models by providing estimates of the extent of frozen-bed conditions.

Glacial land forms indicative of a partly frozen bed

AbstractIn parts of the core area of the Fennoscandian ice sheet relict periglacial surfaces occur. The boundary between periglacial and glacial landscapes is often sharp and erosional, with fluting truncating patterned ground. The periglacial surfaces are older than the last ice sheet and are interpreted to represent patches of continuous frozen-bed conditions. A specific land-form assemblage occurs at the edges of such patches. On the basis of three type localities along the eastern rim of the Scandinavian mountains, four thermal boundary land forms, characteristic of the frozen-patch environment, are defined. Stoss-side moraines and transverse till scarps, not previously described, are interpreted to have formed in detachment zones where soil frozen to the glacier overlies thawed soil. The detachment zones are located where subglacial warming raises the phase-change surface (water/ice) until it intersects the soil layer up-and down-glacier from residual frozen-bed patches. The up-glacier ends of frozen-bed patches are located on topographic highs, but down-glacier the location of lateral sliding boundaries is occasionally independent of topography. The identification of relict surfaces and thermal boundary forms can improve paleo-ice-sheet models by providing estimates of the extent of frozen-bed conditions.

Pleistocene sediment sources, debris transport mechanisms, and depositional environments: a Bering Glacier model applied to northeastern Appalachian Plateau deglaciation, central New York

A modified ice-tongue model suggests that subglacial, saturated, fine sediment derived from local bedrock sources reduced basal shear strength and lowered the ice surface gradient sufficiently to produce ice tongues 20 km long in all major north-south oriented valleys on the northeastern Appalachian Plateau, while adjacent uplands were virtually ice-free. Associated environments of deposition produced two different landform assemblages, one representative of active ice retreat in through valleys and another that depicts widespread stagnation in non-through valleys. Pebble count data indicate that sediment transport by glacial flow was important to the moraine-building process, but the occurrence of isolated kame fields suggests an origin linked to inwash from major upland tributaries. All coarse valley fill (sand and gravel) is derived from two basic sources: (1) re-worked upland drift, and (2) resedimented debris from upvalley sources, including the glacier. Processes common to through valleys favor upvalley sources and active ice landforms, whereas inwash and stagnant ice sedimentation are typical of non-through valleys. Although extensive ice-free uplands served as a source of some fine sediment, a comparison of sediment volume to upland area indicates that inwash processes could not have yielded sufficient fines to account for the volume of fine sand and silt found within the valley fill. Meltwater flow via subglacial tunnels discharged saturated, fine sediment directly into proglacial lakes and served as the major source and transport mechanism for most sand and silt. The Laurentide deglacial environment throughout the upper Susquehanna region was characterized by proglacial lakes, detached remnant ice masses, dead-ice sedimentation and collapsed ice tongues. Stagnation and downwasting in ice-contact lakes peripheral to the eastern Bering Piedmont Glacier, Alaska, serve to depict analog conditions for retreat in central New York.

Mega‐scale glacial lineations and cross‐cutting ice‐flow landforms

AbstractLandsat images reveal a previously unsuspected large‐scale pattern of streamlining within drift that is assumed to reflect former phases of ice flow. Such a glacial grain can be regarded as a landform assemblage comprised of a number of components. Drumlins and megaflutes form part of the pattern, but in addition there are two previously undocumented ice‐moulded landform elements: streamlined lineations of much greater proportions, referred to as mega‐scale glacial lineations, and a distinctive cross‐cutting topology within the grain.The ice‐moulded landform assemblage is described and illustrated with reference to examples from Canada. Possible modes of genesis of such landforms are discussed and their glaciological implications outlined. The discovery of this pattern indicates the pervasive nature of subglacial deformation of sediment, and demands a radical re‐interpretation of ice sheet dynamics.

A critical review of methods used in the appraisal of onshore sand and gravel resources in Britain

The systematic assessment of British onshore sand and gravel resources has been based traditionally on walk-over geological surveys supported by specially commissioned programmes of drilling, pitting, sampling and, more recently, by geophysical surveying. Various other, more cost-effective methods of resource appraisal are now being encouraged. These procedures involve minimal sampling and are based on a combination of geomorphological mapping based on the interpretation of air photographs, analysis of glaciofluvial sediment—landform assemblages and general models of Quaternary landscape evolution. It is argued strongly that no specific resource appraisal procedure will succeed universally because of the diverse nature of sand and gravel deposits. In order to judge the utility of such procedures in Britain, it is possible to subdivide the country into three provinces of contrasting geomorphology and Quaternary geology on the basis of glacierization during the Devensian, pre-Devensian glacierization only, and no glacierization. The principal sand and gravel resources of each terrain are summarised and compared from the point of view of resource appraisal. The model proposed for Britain may be applicable in other regions of the world that have been affected by Quaternary glaciations.

The deglaciation of Glen Croulin, Knoydart

Synopsis The remarkable glacial geology of Glen Croulin has resulted from the interaction of regional ice flowing down Loch Hourn with local ice in Glen Croulin. The regional ice in Loch Hourn dammed up the valley mouth, while local ice occupied the upper part of the glen. This interaction probably dates from the Loch Lomond Stadial. The complex assemblage of landforms in Glen Croulin is interpreted here as a suite of ice marginal moraines and terraces, implying that the deglaciation occurred by active retreat as opposed to stagnation. A detailed picture of the pattern of this decay can be established and leads to the conclusion that the local ice in Glen Croulin reached its maximum extent and had begun to retreat prior to the maximum of the regional Loch Hourn ice.

The last glaciation and relative sea level history of Northwest Ellesmere Island, Canadian high arctic

AbstractPhilips Inlet and Wootton Peninsula are located at 82°N and 85°W on the northwest coast of Ellesmere Island and are composed of three bedrock controlled zones: (1) 900 m undulating plateau dissected by fiords; (2) a deeply fretted cirque terrain >1200m; (3) a 300m plateau bounded by coastal cliffs. Each zone contains different glacier morphologies and these control glacigenic sediment and landform assemblages. The extent of the last glaciation is mapped using the distribution of moraines, kames, meltwater channels and glacimarine sediments. Glaciers advanced on average <10 km from their present margins and many piedmont lobes coalesced and floated in the sea. Morainal banks were deposited at the grounding lines of floating glaciers, and where debris‐charged basal ice occurred, subaqueous fans were deposited upon deglaciation. Marine shells dating 20.2 ka BP (<2km from present ice margin) and 14.9ka BP (from a morainal bank) document full glacial marine fauna. Thirty‐three radiocarbon dates document glacier retreat patterns and are used to reconstruct the postglacial sea level history (glacioisostatic rebound pattern). An equidistant shoreline diagram is constructed using the 8.5ka BP shoreline as a guide. Tilts from 0.73‐0.85m/km are calculated for this shoreline. Using two firm control points and tilts from elsewhere on northern Ellesmere Island, the 10.1 ka BP (full glacial) marine limit descends from 117m as at the fiord heads to 63 m asl at the north coast. Deglaciation started with a pronounced calving phase throughout the field area between 10.1 and 7.8ka BP. This chronology is similar to that from northeast Ellesmere Island and attests to an early Holocene warming trend recorded in high arctic ice cores. A maximum lag of 2.1 ka exists between the field area and locations to the south of the Grant Land Mountains suggesting differences in glacioclimatic regimes on either side of the mountain range. Persistent reconstructions of all‐pervasive ice sheets for the last glaciation of the area are obsolete and should be abandoned.

Tertiary coastal dunes of the Eucla Basin, Australia

On the northeast margin of the Nullarbor Plain in western South Australia, there is preserved an assemblage of coastal aeolian landforms that includes coastal dune, dune ridge and possible beach ridge. One of these landforms is the Ooldea Range, a 650 km long coastal dune that lies 25–300 km from the present coast. These landforms are believed to have formed at the end of the Eocene, after maximum marine transgression in the Eucla Basin. The Ooldea, Barton and Paling ranges formed in a tectonically stable region of topographically subdued terrain. Their orientation and position may be related in part to crustal fractures that were active during initial break-up of Australia and Antarctica. The large quantities of sand required for their construction were supplied to the coast by rivers which drained a hinterland of various suitable source rocks. Growth may have begun as chains of barrier islands, which amalgamated to form large coast-parallel dunes during progradation. These coastal dunes provide evidence about climate at and after the time of their formation. Their formation indicates an atmospheric circulation of at least moderate intensity and prevailing winds with a major westerly component. This occurred at a time when the climate is likely to have been temperate. If the interpretation of the dunes age is correct, they may be viewed as landforms bearing testimony to the global change in climate which occurred at the end of the Eocene. Their excellent preservation in the landscape today, some 34–37 million years after formation, is remarkable. Implied, is a degree of aridity for much of the remainder of the Cainozoic. This appears to have been more significant in the Nullarbor Plain region than in the southeastern part of Australia. Other factors responsible for their preservation are likely to include vegetation cover, the permeability of their quartz sands, subsequent history of sea level and hydrodynamics of the basin.

Land system mapping using landsat multispectral scanner imagery in the Willandra lakes region of western New South Wales

SUMMARY Satellite imagery provides a cost effective method of mapping distinctive assemblages of landforms, soils and vegetation over large areas, especially where access is poor. This study reports on an evaluation of supervised and unsupervised techniques of classifying Landsat reflectance information in the Wiilandra Lakes World Heritage region. The accuracy of mapping derived from Landsat information compares very favourably with land systems mapping on the ground.

Sand dune dynamics and sand sea evolution

Abstract Sandy deserts comprise complex landform assemblages, which require study at all scales to explain thei spatial and temporal evolution. The Wahiba Sands, in the Sultanate of Oman, a near perfect example of a sand sea, is ideal for such an investigation.

Glacial geomorphology and chronology in the Selamiut Range – Nachvak Fiord area, Torngat Mountains, Labrador

The Selamiut Range of the Torngat Mountains, northern Labrador, rises to over 1700 m above sea level and constituted a barrier to eastward-flowing Laurentide ice during former glaciations. Local and regional ice has left an assemblage of landforms exhibiting cross-cutting relationships. Three glacial phases are recognized in the area. The oldest and most extensive (the Ivitak phase) is marked by high-elevation till deposited when regional and local ice coalesced. At this time regional ice flowed eastward down Nachvak Fiord while interfiord highlands extended above the ice as nunataks. During a late Ivitak phase a large proglacial lake was dammed in the lower McComick Valley at 80 m above sea level when regional and local ice in Nachvak Fiord blocked the local drainage. During the subsequent Nachvak phase, lakes were dammed in the lower McCornick Valley at 67 and 53 m above sea level for ca. 3000 years by Laurentide ice alone. The Superguksoak had three subphases when local cirque glaciers expanded up to 5 km beyond their present limits. The Holocene marine limit around 33 m reflects the small ice load influencing Nachvak Fiord, or very late deglaciation of the Ivitak Cove area.The chronology of these glacial and proglacial deposits is based on their spatial relationships as well as pedology and lichenometry. Seventy-nine soil pits excavated to the base of the Cox horizon indicate the relative duration of weathering since deglaciation. Absolute ages for the soils are estimated to be > 40–40 ka BP for the Ivitak phase, 23–17 ka BP for the Nachvak phase, and 12–5 ka BP for Superguksoak I. Measurements of Rhizocarpon geographicum indicate that prominent Superguksoak-phase moraines bordering the present-day cirques were abandoned approximately > 4000, 3000, and 1500 years BP. Collectively these data are compared with earlier fieldwork in northern Labrador, and some discrepancies are discussed.

The Late Devensian periglaciation of upland Scotland

A wide variety of Late Devensian periglacial landforms developed on Scottish mountains both before ca. 13,000 BP and during the Loch Lomond Stadial of ca. 11,000-10,000 BP. Nearly all such features are now inactive. Late Devensian periglacial weathering produced three types of regolith mantle (openwork block deposits, sandy diamicts and silt-rich frost-susceptible diamicts), each of which supports a characteristic assemblage of relict landforms. On upper slopes these include large-scale sorted circles and stripes, earth hummocks and nonsorted relief stripes, sorted and nonsorted solifluction features, massive boulder sheets and lobes, and nivation benches. Talus, protalus ramparts, rock glaciers and alluvial fans also developed at the base of mountain slopes. The distribution of Late Devensian periglacial features on Scottish mountains is locally controlled by topography, the response of underlying rocks to periglacial weathering and the limits of former glaciers. Regional variations in the altitude of certain forms of Loch Lomond Stadial age (particularly protalus ramparts and rock glaciers) indicate a decrease in former snowfall eastwards across the Scottish Highlands and northwards from the Highland Boundary Fault. Several upland periglacial features are also diagnostic of former permafrost, and complement palaeotemperature reconstructions based on ice-wedge casts and the equilibrium firn line altitudes of stadial glaciers. These suggest that under stadial conditions mean January temperatures at 600 m and 1000 m on mountains in the Western Grampians must have been no higher than −20°C and −23°C respectively, and possibly several degrees lower.

SIGNIFICANCE OF LANDFORMS IN SOUTHEAST MICHIGAN∗

An assemblage of landforms in a complex interlobate area in southeast Michigan may be used to identify the surficial contact between Saginaw and Huron-Erie drifts even though the sediments from both glacial lobes appear similar and cannot be reliably differentiated in the field. The correct placement of the boundary is confirmed by X-ray diffraction data for clay-sized particles from more than forty drift samples. This study demonstrates that in some instances morphology may equal or exceed the usefulness of rock-, soil-, and geologic-climate units for the determination of certain stratigraphic relationships.

Martian channel morphology: Maja and Kasei Valles

Detailed geomorphic mapping from Viking imagery of selected portions of Kasei Vallis, Maja Vallis, and vicinity reveals numerous similarities of channel morphology to erosional and depositional features of the Channeled Scabland. Characteristic scabland landforms which occur in Kasei and Maja Valles include erosional grooves, streamlined uplands and hills, scour zones around flow obstacles, inner channels with erosional head cuts, breached ridges and basin (crater) rims, pendant forms (bars?), erosional terracing of streamlined hills and channel margins, and possible midchannel bars. These features constitute an assemblage of landforms which on earth is most characteristic of catastrophic flood channeling in jointed bedrock. Prominent mass wastage and sapping features are associated with the high‐wall relief in lower Kasei Vallis. Many cliffs along the channel margins exhibit steep upper slopes and gentler lower talus slopes which form the spur‐and‐gully topography that has also been described along chasma walls in the Valles Marineris. Landslides, debris fans, and debris cones can also be recognized. Much less wall modification occurs in the shallower Maja Vallis. Probably, the steep escarpments of Kasei were created by tectonic processes and subsequent channel incision. These escarpments later receded by mass wasting and sapping.

Pool and drain morphology: an assemblage of ephemeral landforms from the Upper Swash Zone of a Sandy Beach

Pool and drain morphology: an assemblage of ephemeral landforms from the Upper Swash Zone of a Sandy Beach

GLACIAL LANDFORMS: DES MOINES DRIFT SHEET, IOWA

ABSTRACT Cluster analysis of data from county soils reports and from aerial photographs produced three regions with distinctly different assemblages of glacial landforms. The northern region is composed of bogs, kames, terraces, and cross-lineated to circular feature ice-stagnation moraine. The central region is characterized by level, poorly drained soil and nonpatterned ground moraine. The marginal region consists of lineated to cross-lineated ice stagnation features. These clusters are associated with differences in the bedrock topography. The success of this study in defining coherent, logical clusters of counties with similar landforms indicates that the landform data available in county soils reports can be employed in regional analysis even when using county-sized sample cells if the study does not require the establishment of definitive regional boundaries.

Some problems in the quaternary evolution of the landforms of northern Botswana

Northern Botswana is notable for the remarkable juxta-position of the wetland landscapes of the Okavango Delta, and the semi-arid landforms of the closely adjacent Makgadikgadi basin. There is much evidence to suggest that a great pluvial lake occupied the latter at various times in the Pleistocene and Holocene, and may on one or more occasions have formed a very large and continuous body of water with the Okavango - Mababe - Ngami depression. Changing climate and neotectonism have both clearly played a part in the evolution of a very complex assemblage of landforms. The study of these landforms may throw much light on the nature of geomorphic processes under differing climates; on the pattern and chronology of climatic change; on the incidence of neotectonism within the area; and on the history of the movement and settlement of Stone Age man, whose artefacts are found in abundance throughout the region. A very tentative chronology of events is put forward. Nordbotswana ist bekannt für das bemerkenswerte Nebeneinander der Feuchtgebiete des Okavango Deltas und der semiariden Oberflächenformen des dicht benachbarten Makgadikgadi-Beckens. Höchstwahrscheinlich bestand zu verschiedenen Zeiten des Pleistozäns und Holozäns im Makgadikgadi-Becken ein großer pluvialzeitlicher See, der zeitweilig eine zusammenhängende Wasserfläche mit der Okavango - Mababe - Ngami Depression gebildet haben könnte. Sowohl Klimawechsel als auch Neotektonik haben eine Rolle bei der Entwicklung dieses Landschaftskomplexes gespielt. Die Untersuchung dieser Oberflächenformen ergibt Hinweise auf die Art der Geomorphodynamik unter verschiedenen Klimaten, auf Verbreitung und Chronologie der Klimawechsel, auf das Vorkommen von Neotektonik, auf Entwicklungsgeschichte, Wanderungsbewegungen und Siedlungen des steinzeitlichen Menschen, dessen Werkzeuge in diesem Gebiet reichlich zu finden sind. Es wird eine vorläufige chronologische Einordnung dieser Ereignisse vorgelegt.

The shaping and interpretation of large residual granite boulders

Abstract Much evidence supports the view that granite boulders and the several minor features sculptured on them are essentially etch forms. Flared slopes, platforms, and notches, and several variants and combinations, are all initiated at the weathering front. They have been revealed by the stripping of the regolith, and their exposure has taken place not in a single event but in several phases. As has been suggested in respect of similar landform assemblages found on inselbergs, the morphology of the boulders reflects the geomorphological histories of the areas in which they occur.

Patterns of Present Sub-Aerial Erosion and Landforms in Mid-Wales

Patterns of Present Sub-Aerial Erosion and Landforms in Mid-Wales

Characteristics and Origin of a Precambrian Pediment

The unconformity beneath the Torridonian (late Precambrian) sediments of northwest Scotland represents one of the most ancient of fossil landform assemblages. Cut across crystalline Lewisian rocks, it is highly irregular in most places, the relief locally reaching 1,000 m. This rugged surface is little weathered. In the extreme north, however, the unconformity generally parallels the major stratification of the sediments above. Before its burial, this planar surface was weathered to depths of several metres then partly stripped of its altered mantle. A solitary hill of gneiss represents the only major relief in the unconformity within this northern district. A piedmont alluvial fan environment is suggested by the overlying arkosic sediments. The planar, weathered surface and the solitary hill thus appear analogous to a pediment and knoll buried beneath alluvial fan deposits. Vertical variations in the sediments are consistent with the planar surface having formed contemporaneously with sedimentation as a ...