The Medial Moraines of the Lower Glacier de Tsidjiore Nouve, Valais, Switzerland

Abstract

ABSTRACT. The two medial moraines of the Glacier de Tsidjiore Nouve a re nourished by rock de bris revealed a t the surface by progressive a bla tion down-glacier. The sources of th e moraine appear to be rock outcrops ma rgina l to or above the Pigne d'Arolla ice fall , much of the d etri tus entering the glacier via c revasses either at the summit or the base of the ice fall. The role of differential a blation in the emergence of the moraines as relief features is illuminated by measurements made in the late summ ers of 197 1 and 1972. The eventua l decl ine of the moraines down-glacier is related to factors of reducing d ebris supply, lateral sliding and accelerated abla ti on due to attenuation of the de trita l cover to a mean thickness of 1 cm or less. A model of moraine development, different in several respects from that proposed by Loomis ( 1970) for the Kaskawulsh Glacier, Alaska, is outlined. RESUME. us moraines medianes de la par/ie inferieure du glacier de Tsidjiore Nouve dans le Valais, Suisse. Les deux moraines medianes du glacier de Tsidjiore Nouve sont nourries par des debris de roe qui a ppara issent a la surface en raison de l'ablation progressive a u bas du glacier. Les sources d e la mora ine semblent ctre un affieurement rocheux, marginal a la cascade d e seracs d e la Pigne d'Arolla, beaucoup de de tritus pene trant dans le glacier pa r les crevasses form ees a la base d e la cascade. Le role de l'ablation differentielle dans l'emergence des moraines comme des reliefs, est illustre par les mesures faites en fin d 'ete 1971 et 1972. L'eve ntuel abaissement d es moraines a u bas du glacier es t en relation avec les facteurs d e reduction de l'approvisionnement en debris, avec le glissement la teral , et avec l'accelera tion de l'ablation en raison de l'amincissement de la couche d e debris jusqu'a une epaisseur moyenne de 1 cm ou moins. On evoq ue un modele de developpement de moraine, different a plusieurs egards de celui propose par Loomis ( 1970) pour le K aska wulsh Glacier, Alaska. (Fig. I ). The glacier is notable for its considerable burden of supragla cial moraine, largely composed of blocks and finer fragments of light grey gneiss of the Arolla Series of the D ent Blanche Nappe and highly fractured darker schists of the Schistes Lustres Series. This material forms two well-defined m edial moraines, ea ch approximately I km in length, which at their downglacier ends spread to m erge with marginal morainic d ebris. Of the two moraines that to the south (right) is markedly broader and higher (rea ching a width of 101 m and a maximum elevation of 22.25 m above nearby bare ice, comp a red with corresponding figures of 59 m and 6 m for the northern m oraine), a nd will accordingly be referred to throughout this paper as the main moraine; that to the north (left) is termed th e subsidiary moraine.

Debris transport by Loch Lomond Readvance glaciers in Northern Scotland: Basin form and the within‐valley asymmetry of lateral moraines

“…Boulton (1 978) and Boulton and Eyles (1 979) have argued that at the confluence of ice streams, the arrangement of flow lines serves to elevate debris from the basal transport zone into a longitudinal debris septum The surface expression of such septa, in the form of discrete debris bands exhibiting typical 'subglacial' grain-size distributions and clast characteristics, have been noted on temperate valley glat ier5 by several authors (e g Croot, 1978, Vere, 1986, Gomez and Small, 1985 If medial moraines evolve into positive relief features some lateral spredding of material can occur, distributing debris over a wider area of the snout (Small and Clark, 1974, Eylcs and Rogerwn, 1 Y 78)…”

Structure and Debris Characteristics of Medial Moraines in Jotunheimen, Norway: Implications for Moraine Classification

“…The presence of lateral slopes, and the consequent debris mobilzation, is the result of differential glacier-surface ablation due to the locally high debris supply (cf. Small and Clark, 1974).…”

Sedimentary facies and landform genesis at a temperate outlet glacier: Soler Glacier, North Patagonian Icefield

“…Supraglacial debris transport has a profound influence on the distribution of sediment at the ice margin, whereas the form and structure of supraglacial debris features are important controls on the distribution of landforms and sedimentary facies in front of valley glaciers (Boulton & Eyles, 1979; Eyles, 1979). Supraglacial debris is often organized into medial and lateral moraines, both of which are important features of high‐level sediment transport within these glaciers (Small & Clark, 1974; Eyles & Rogerson, 1978a,b;Small et al ., 1979; Gomez & Small, 1983; Rogerson et al ., 1986; Small, 1987; Smiraglia, 1989).…”