Medial Moraines of the Haut Glacier D’arolla, Valais, Switzerland: Debris Supply and Implications For Moraine Formation

Glasser, N. F., Goodsell, B., Copeland, L., Lawson, W. (2006) Debris characteristics and ice-shelf dynamics in the ablation region of the McMurdo Ice Shelf, Antarctica. Journal of Glaciology, 52, 177, pp 223-234 Sponsorship: Antarctica New Zealand; University of Canterbury; TransAntarctic Association; The Leverhulme TrustThis paper presents observations and measurements of debris characteristics and ice-shelf dynamics in the ablation region of the McMurdo Ice Shelf in the Ross Sea sector of Antarctica. Ice-shelf surface processes and dynamics are inferred from a combination of sedimentological descriptions, ground-penetrating radar investigations and through ablation, velocity and ice-thickness measurements. Field data show that in the study area the ice shelf moves relatively slowly (1.5?18.3ma?1), has high ablation rates (43?441mm during 2003/04 summer) and is thin (6?22 m). The majority of debris on the ice shelf was originally transported into the area by a large and dynamic ice-sheet/ice-shelf system at the Last Glacial Maximum. This debris is concentrated on the ice-shelf surface and is continually redistributed by surface ablation (creating an ice-cored landscape of large debris-rich mounds), ice-shelf flow (forming medial moraines) and meltwater streams (locally reworking material and redistributing it across the ice-shelf surface). A conceptual model for supraglacial debris transport by contemporary Antarctic ice shelves is presented, which emphasizes these links between debris supply, surface ablation and ice-shelf motion. Low-velocity ice shelves such as the McMurdo Ice Shelf can maintain and sequester a debris load for thousands of years, providing a mechanism by which ice shelves can accumulate sufficient debris to contribute to sediment deposition in the oceans.Peer reviewe

Section: Black Island Medial Moraine Area Sediment-landform Assemblagsupporting

confidence: 89%

Debris characteristics and ice-shelf dynamics in the ablation region of the McMurdo Ice Shelf, Antarctica

Glasser¹,

Goodsell

Copland

et al. 2006

“…Consequently, it is only at some distance below the junction point, where the effect of differential ablation starts to dominate the strong downward movements, that the ice-cored medial moraine starts to form. The surface debris does not immediately give rise to a medial moraine as described by Gomez and Small (1985)in their model of ice-stream interaction moraines. Without surficial detritus covering the marginal zones of the tributaries where they coalesce, the advection of the surface depression initially formed at the junction point would lead to the formation of a longitudinally aligned depression, and not to a medial moraine that rises above the surrounding ice.…”

Section: Medial Morainementioning

confidence: 96%

A three-dimensional numerical model of the confluence area of Unteraargletscher, Bernese Alps, Switzerland

Gudmundsson

1999

With the use of a numerical three-dimensional (3-D) model the flow dynamics of the confluence area of Unteraargletscher, Bernese Alps, Switzerland, are studied. Previous predictions, based on conceptual two-dimensional models, about flow characteristics at confluence areas are tested against results from the fully 3-D model. Measured winter velocities are used for model verification. Despite some consistent systematic differences, good overall agreement between measured and calculated surface velocities is obtained. The calculated vertical strain-rate variation with depth is in good agreement with available measurements from boreholes. The ice is found to be almost three times stiffer than standard estimates of rheological parameters for glacier ice would predict. The model predicts a complicated yet realistic pattern of vertical velocity variation along the surface. The most noticeable features of the vertical velocity distribution across the surface are listed, and their relation to topographic surface undulations and the overall dynamics of the confluence discussed. In accordance with previous results from analytical models, a strongly localized surface trough and a concomitant negative (downward orientation) vertical velocity anomaly develop at the junction point. Although depth-integrated strain rates are positive (extension), the basal layer is compressed vertically. The ice-cored medial moraine is formed by differential ablation. The flow mechanics of the confluence area play only an indirect role, by enabling transfer of debris-covered marginal ice towards the confluence center. In the absence of differential ablation, an elongated surface depression would be formed in the down-glacier direction from the junction point instead of an elevated ice-cored medial moraine.

“…The possiblity cannot be excluded that a certain amount of englacial or subglacial debris, derived from material that entered the crevasses and from basal erosion, may contribute to the debris supply of the moraines. However, no evidence such as the nearly vertical englacial debris bands, like those cited by Gomez and Small (1985) for Haut Glacier d'Arolla, has been found on Ghiacciaio dei Forni. Further development of the medial moraines on Ghiacciaio dei Forni may be briefly summarized as follows: Fig.…”

Section: The Morphology and Development Of The Medial Morainesmentioning

confidence: 89%

“…The various processes determining the origin and the development of medial moraines have already been indicated by some of the researchers mentioned above (for example, see the models proposed by Small and Clark, 1976;Eyles and Rogerson, 1978a;Gomez and Small, 1985). These researchers have stressed the complex relations between debris supply, lateral compression of the ice streams, and differential ablation.…”

Section: Fragmentationmentioning

confidence: 89%

“…are one of the most distinctive features of the surface morphology of glaciers and they have been widely studied. Models of their formation and evolution have been derived (Small and Clark, 1974;Eyles and Rogerson, 1978a, b;Boulton and Eyles, 1979;Small and others, 1979;Gomez and Small, 1985). As far as the Italian Alps are concerned, interest in epiglacial morphology is very recent.…”

Section: Medial Morainesmentioning

confidence: 99%

See 1 more Smart Citation

The Medial Moraines of Ghiacciaio Dei Forni, Valtellina, Italy: Morphology and Sedimentology

Smiraglia

1989

Two distinct medial moraines are located on the tongue of Ghiacciaio dei Forni (Rhaetian Alps, Italy); they are formed by the confluence of three ice streams. The two ice-cored medial moraines originate from rock outcrops situated below the snow line. The moraines, which on the surface comprise angular clasts, extend for approximately 2 km and reach a maximum height of 10 m. Nourishment of the moraines seems to be due primarily to the supraglacial debris derived from the rock walls. Measurements made in the late summer of 1985 provided evidence of the role played by differential ablation in the development of these moraines. Sedimentological analysis further confirmed the mainly supraglacial origin of the debris comprising the moraines.