Medial Moraines Research Articles

The Nature and Origin of Debris Layers within Glacier De Tsidjiore Nouve, Valais, Switzerland

The development of medial moraines on the Glacier de Tsidjiore Nouve is related to numerous englacial debris layers of limited dimensions, which are exposed at the glacier surface below the Pigne d’Arolla ice fall. Previous research has suggested that such layers result either from high-level transport of debris, derived from rock weathering and/or glacial erosion in the accumulation zone, or from shearing up of subglacial debris owing to intense compressive stresses in the glacier. The morphology of the debris layers is investigated in the field, and samples are subjected to particle-size analysis. It is concluded that constituent debris is derived largely from exposed faces of rock between the upper and lower firn basins, but that a subglacial component is present. Entry of the debris into the glacier is possibly by way of crevasses on the lower firn basin.

A Devensian Medial Moraine in Jura

Synopsis On the western side of Jura, there exists a remarkable 3.5 km linear suite of parallel boulder belts. The feature originates at 450 m O.D. at the western foot of Beinn an Oir, one of the Paps of Jura, and extends seaward to 30 m O.D. where it ends at a shallow lochan that lies at the junction between the feature and a high late-glacial marine shoreline. The boulder complex is composed in places of up to 4 parallel lines of dominantly angular Dalradian quartzite blocks (the local bedrock), each line rarely exceeding 27 m in width and 2.5 m in vertical thickness. The boulders, including several erratics, range from 0.2 to 1.3 m in length and are here interpreted as a large medial moraine that formed during the waning of the Devensian ice sheet in western Scotland.

The Formation of Medial Moraines on Alpine Glaciers

AbstractField investigation of six medial moraines on glaciers near Arolla, Valais, Switzerland, has revealed that all are nourished by englacial till. This is probably derived from supraglacial point-sources on the accumulation zones of the glaciers, and is released in increasing quantities on the ablation zones, where it emerges diffusely or by way of clearly defined transverse or longitudinal debris bands. Possible mechanisms of formation of these debris bands are reviewed, and it is proposed that the transverse bands originated as crevasse fillings on the accumulation zones. Morphologically all six moraines display waxing sections (of increasing height and breadth), related to development of a protective till cover and resultant differential ablation of the glacier surface. Two only display waning sections (of decreasing height), resulting from lateral sliding of till and “inverted” differential ablation resulting from extreme attenuation of till cover. Four “moraine-types” (related to nature of debris supply and detailed morphology) are identified in the Arolla area. It is believed that these may form the basis for a classification of medial moraines.

The Formation of Medial Moraines on Alpine Glaciers

AbstractField investigation of six medial moraines on glaciers near Arolla, Valais, Switzerland, has revealed that all are nourished by englacial till. This is probably derived from supraglacial point-sources on the accumulation zones of the glaciers, and is released in increasing quantities on the ablation zones, where it emerges diffusely or by way of clearly defined transverse or longitudinal debris bands. Possible mechanisms of formation of these debris bands are reviewed, and it is proposed that the transverse bands originated as crevasse fillings on the accumulation zones. Morphologically all six moraines display waxing sections (of increasing height and breadth), related to development of a protective till cover and resultant differential ablation of the glacier surface. Two only display waning sections (of decreasing height), resulting from lateral sliding of till and “inverted” differential ablation resulting from extreme attenuation of till cover. Four “moraine-types” (related to nature of debris supply and detailed morphology) are identified in the Arolla area. It is believed that these may form the basis for a classification of medial moraines.

Patterned Ground on an Active Medial Moraine, Jotunheimen, Norway

AbstractSorted circles and nets formed on the surface of the principal medial moraine on Storbreen, Jotunheimcn, Norway, are described. These consist of “islands” of coarse sand, granules, and small pebbles, surrounded by pebbles and cobbles and underlain by small domes of glacier ice. It is suggested that patterned ground formation on the moraine results from differential ablation in areas of thin (<200 mm) debris cover near the glacier snout, where melting is relatively rapid. It is unlikely that supraglacial patterned ground could survive deposition.

Patterned Ground on an Active Medial Moraine, Jotunheimen, Norway

AbstractSorted circles and nets formed on the surface of the principal medial moraine on Storbreen, Jotunheimcn, Norway, are described. These consist of “islands” of coarse sand, granules, and small pebbles, surrounded by pebbles and cobbles and underlain by small domes of glacier ice. It is suggested that patterned ground formation on the moraine results from differential ablation in areas of thin (<200 mm) debris cover near the glacier snout, where melting is relatively rapid. It is unlikely that supraglacial patterned ground could survive deposition.

Rhombus and Rhomboid Parallelogram Patterns on Glaciers: Natural Indicators of Strain

AbstractSubtle rhombus and rhomboid parallelogram patterns occur on Vaughan Lewis Glacier and the Gilkey Glacier System, Juneau Icefield, Alaska. The patterns are within the firn at the firn-ice interface, are formed by differential recrystallization within narrow preferred zones, and are apparently manifestations of stresses transferred upward from the glacier ice. On the glaciers of the Gilkey System the patterns occur where intense lateral shortening is indicated by abrupt convergence of medial moraines and an abundance of extension crevasses. The short axes of the rhombi and the obtuse angle bisectors of the rhomboids are subparallel to the strike of extension crevasses, therefore to the axis of shortening. The long axes of the rhombi and the acute angle bisectors of the rhomboids are parallel to the foliation, and ice-flow direction. The angles of the parallelograms are variable locally, but average 105° and 75°; the variation seems to reflect intensity and duration of stress. Similar parallelograms occur within the troughs of wave bulges below the Vaughan Lewis Icefall. In the wave bulges, the foliation arcs parallel the wave. The long axes of the rhombi and acute angle bisectors of the rhomboids parallel the foliation around the foliation arc. The short axes of the rhombi and the obtuse angle bisectors of the rhomboids parallel the strikes of radial crevasses, are perpendicular to the direction of extension, and form a fan divergent down-stream. The precise mechanisms and conditions of formation of the parallelograms are not yet understood. Preliminary strain-rate measurements suggest, however, that correlations exist between the orientations of the principal strain-rates and the axes of the patterns, and between the magnitude of the strain-rates and the axial lengths of the patterns.

Rhombus and Rhomboid Parallelogram Patterns on Glaciers: Natural Indicators of Strain

AbstractSubtle rhombus and rhomboid parallelogram patterns occur on Vaughan Lewis Glacier and the Gilkey Glacier System, Juneau Icefield, Alaska. The patterns are within the firn at the firn-ice interface, are formed by differential recrystallization within narrow preferred zones, and are apparently manifestations of stresses transferred upward from the glacier ice. On the glaciers of the Gilkey System the patterns occur where intense lateral shortening is indicated by abrupt convergence of medial moraines and an abundance of extension crevasses. The short axes of the rhombi and the obtuse angle bisectors of the rhomboids are subparallel to the strike of extension crevasses, therefore to the axis of shortening. The long axes of the rhombi and the acute angle bisectors of the rhomboids are parallel to the foliation, and ice-flow direction. The angles of the parallelograms are variable locally, but average 105° and 75°; the variation seems to reflect intensity and duration of stress. Similar parallelograms occur within the troughs of wave bulges below the Vaughan Lewis Icefall. In the wave bulges, the foliation arcs parallel the wave. The long axes of the rhombi and acute angle bisectors of the rhomboids parallel the foliation around the foliation arc. The short axes of the rhombi and the obtuse angle bisectors of the rhomboids parallel the strikes of radial crevasses, are perpendicular to the direction of extension, and form a fan divergent down-stream. The precise mechanisms and conditions of formation of the parallelograms are not yet understood. Preliminary strain-rate measurements suggest, however, that correlations exist between the orientations of the principal strain-rates and the axes of the patterns, and between the magnitude of the strain-rates and the axial lengths of the patterns.

Sedimentology of medial moraines on Berendon Glacier, British Columbia, Canada: Implications for debris transport in a glacierized basin

The character of sediments from medial moraines on Berendon Glacier, British Columbia, reflects periglacial processes rather than direct glacial erosion and transport. Sediments are passively transported as talus by the glacier, and a distinct sedimentology can be contrasted with lodgement tills. Medial morane sediment is derived from a number of sources and is transported on the glacier surface and at depth near the glacier bed — there is no evidence of either textural evolution with increasing distances of glacial transport or enhanced scour of the glacier bed in the vicinity of medial moraines. Particle-size distribution of both medial moraine debris (supraglacial morainic till) and lodgment tills is found to be independent of source rock. A bimodal grain-size distribution widely reported from the analysis of far-traveled Pleistocene tills from the mid-latitudes, reflecting the crushing characteristics of component minerals in the source rock, is not exhibited by tills from Berendon Glacier which have well-defined lithological sources. This reflects the short distances of debris transport by the glacier and is considered to be typical of other temperal valley glaciers.

A Framework for the Investigation of Medial Moraine Formation: Austerdalsbreen, Norway, and Berendon Glacier, British Columbia, Canada

AbstractMorphology of medial moraines on Austerdalsbreen, Norway, and Berendon Glacier, British Columbia, depends upon englacial debris supply. Major sub-types of this "ablation-dominant" model are related to the zone of debris entrainment relative to the firn line, and the manner of entrainment.On Austerdalsbreen, debris derived from extraglacial bedrock slopes is entrained via crevasses at the confluence of two ice-cap outlet glaciers below the firn line. Revelation of crevasse-bound debris generates a distinct ice-cored morphology which is destroyed as crevasse bottoms are revealed down-glacier.On Berendon Glacier ice streams coalesce above and below the firn line. Above the firn line, debris from extraglacial rock outcrops, subnival and subglacial zones, undergoes seasonal sedimentation with snowfall, and extends throughout the ice depth. Distinct moraine morphology in the terminal zone is related to continuing debris supply. Most debris is transported at depth near the glacier base.An "ice-stream interaction" model where medial moraines formed below the firn line from the confluence of ice streams with large lateral moraine load are morphologically controlled by flow, explains morphology on the Berendon Glacier in the main confluence zone only. Down-glacier, this moraine becomes "ablation dominant". A minor "avalanche-type" model is also recognized.

A Framework for the Investigation of Medial Moraine Formation: Austerdalsbreen, Norway, and Berendon Glacier, British Columbia, Canada

AbstractMorphology of medial moraines on Austerdalsbreen, Norway, and Berendon Glacier, British Columbia, depends upon englacial debris supply. Major sub-types of this "ablation-dominant" model are related to the zone of debris entrainment relative to the firn line, and the manner of entrainment.On Austerdalsbreen, debris derived from extraglacial bedrock slopes is entrained via crevasses at the confluence of two ice-cap outlet glaciers below the firn line. Revelation of crevasse-bound debris generates a distinct ice-cored morphology which is destroyed as crevasse bottoms are revealed down-glacier.On Berendon Glacier ice streams coalesce above and below the firn line. Above the firn line, debris from extraglacial rock outcrops, subnival and subglacial zones, undergoes seasonal sedimentation with snowfall, and extends throughout the ice depth. Distinct moraine morphology in the terminal zone is related to continuing debris supply. Most debris is transported at depth near the glacier base.An "ice-stream interaction" model where medial moraines formed below the firn line from the confluence of ice streams with large lateral moraine load are morphologically controlled by flow, explains morphology on the Berendon Glacier in the main confluence zone only. Down-glacier, this moraine becomes "ablation dominant". A minor "avalanche-type" model is also recognized.

Glacier movement, ice structures, and medial moraine form at a glacier confluence, Berendon Glacier, British Columbia, Canada

On Berendon Glacier, Canada, at the asymmetric Y junction of two large valley glaciers, observations of ice velocity, strain rate, and ice structures indicate that the form of a medial moraine is determined by severe lateral compression between the two ice streams. Debris of the moraine is recycled along complex transport paths determined by ice structures. For example, supraglacial debris is precipitated into the confluence zone between the two glaciers forming a subglacial debris reservoir. Debris is evacuated from the reservoir by shearing between the two glaciers and is revealed on the glacier surface as debris dykes and melt-out tills along the contact plane. Important implications regarding the sedimentology of the moraine can be stated. Elsewhere debris is precipitated into transverse crevasses subsequently resulting in transverse till ridges at the glacier surface.Annually-formed wave ogives, bulges in surface ice, and overriding along the glacier contacts result from severe lateral compresssion, and add further diversity to the moraine.Downglacier, confluence ice structures are destroyed by ablation, the pattern of ice flow becomes less complex, unified flow between the two glaciers is established, and a distinct structurally-determined moraine morphology is replaced by one dependent upon the differential ablation of debris covered and clean ice.

Morphology and development of medial moraines: reply to further comments by N. Eyles

Morphology and development of medial moraines: reply to further comments by N. Eyles

Morphology and Development of Medial Moraines: Reply to Comments by N. Eyles

Morphology and Development of Medial Moraines: Reply to Comments by N. Eyles

Morphology and Development of Medial Moraines: Further Comments on the Paper by R. J. Small and M. J. Clark

An abstract is not available for this content. As you have access to this content, full HTML content is provided on this page. A PDF of this content is also available in through the ‘Save PDF’ action button.

Morphology and development of medial moraines: reply to comments by N. Eyles

Morphology and development of medial moraines: reply to comments by N. Eyles

Morphology and Development of Medial Moraines: Reply to Further Comments by N. Eyles

Morphology and Development of Medial Moraines: Reply to Further Comments by N. Eyles

Morphology and Development of Medial Moraines: Comments on the Paper by R. J. Small and M. J. Clark

An abstract is not available for this content. As you have access to this content, full HTML content is provided on this page. A PDF of this content is also available in through the ‘Save PDF’ action button.

Morphology and development of medial moraines: further comments on the paper by R. J. Small and M. J. Clark

Morphology and development of medial moraines: further comments on the paper by R. J. Small and M. J. Clark

Morphology and development of medial moraines: comments on the paper by R. J. Small and M. J. Clark

Morphology and development of medial moraines: comments on the paper by R. J. Small and M. J. Clark