A Tentative Theory of Ogive Formation

Abstract

The dark and light bands on glaciers known as ogives are only found beneath ice falls and avalanche fans. They are not to be confused with sedimentary layering, which may appear similar. Vareschi’s pollen studies are considered in relation to the present theory; his evidence is re-interpreted and shown to support the theory put forward.The Norwegian glacier Austerdalsbreen has a fine double set of ogives, one set on ice from Odinsbreen and the other on ice from Thorsbreen. These ogives are continuous from near the feet of these ice falls down to the end of the main glacier. The ice from the collecting ground of Jostedalsbreen which moves slowly towards the head of these ice falls is normally stratified as seen in the deep crevasses immediately above the ice falls. The high velocity of flow, 2,000 m. per year in the upper part of Odinsbre ice fall, causes the ice to stretch into a thin and heavily crevassed layer which exposes a very high proportion of surface per unit volume to the sun, the rain and the snow. In summer this leads to:(1) crystal changes, primarily of enlargement, (2) an infusion of dirt which blows on to the glacier from the neighbouring snow-free and vegetation-free land surfaces, and (3) water filling the bottom of some of the deeper crevasses, which may later freeze. On the other hand, the ice which passes down the ice falls in winter is largely protected by a mantle of snow; crystal changes then are slow, little dust collects, and less water pours into the crevasses which, instead, are filled with new snow. So the ice reaching the lower part of the ice falls and moving on to form the main glacier, Austerdalsbreen, has been subjected throughout its mass to seasonal differences. These differences seem to be more systematic in the deeper ice, and only when the chaotic surface layers are melted away, do they appear on the surface of Austerdalsbreen as well defined ogives. The greater proportion of blue, bubble-free ice with large crystals in the “summer” ice, is alone sufficient to distinguish it from the lighter-coloured “winter” ice with its more frequent bands of white bubbly ice having very small crystals. But as ablation continues, more and more dust is brought to the surface and this still further darkens the “summer” ice. In addition the darker ice melts more readily and tends to form troughs in the glacier surface which retard stream flow, hold the lingering snows, and trap further dust and dirt. The cracks between large crystals also hold dirt better than the smooth hard white surfaces which occur more frequently in the “winter” ice. Hence the ogives remain distinct throughout their journey down Austerdalsbreen. Near the snout the medial moraine is very abundant along the darker bands deriving from Thorsbreen, and this further supports our view that this darker ice was in the ice fall in summer when most debris falls from the rock walls on to the ice fall.

Structural glaciology of a temperate maritime glacier: lower fox glacier, new zealand

“…4) and below the lower icefall, although their lateral continuity is severely obscured by dense crevassing in this latter zone. The band-ogives below the upper icefall are visible on aerial photographs but much King and Lewis 1961;Atherton 1963;Goodsell et al 2002). The light ogive bands appear as white to light-grey, and the dark ogive bands appear as a dark shade of brown.…”

“…Leighton 1951;Miller 1952;King and Ives 1956;Posamentier 1978) and the 'summer versus winter passage' hypothesis (e.g. Washburn 1935;Nye 1958Nye , 1959King and Lewis 1961;Fisher 1962). The shearing hypothesis is that band-ogives are the surface expression of major shear planes, resulting from compressive flow down-glacier of an icefall.…”

“…On this basis, delineating the mechanism of band-ogive formation at Fox Glacier is problematic. Given the narrow band-ogive width (c. 30-40 m) and long icefall (c. 2.5 km), and typical surface velocities of up to 1 m d -1 (Purdie et al 2008a), each band-ogive 'pair' cannot represent one year's passage through the upper icefall, in contrast to the theories of Nye (1958Nye ( , 1959, King and Lewis (1961) and Fisher (1962). This is because the icefall is too long (2.5 km) for a transverse crevasse to propagate through the icefall within one year.…”

Morphology, Surface Characteristics, and Flow Velocity of Soler Glacier, Patagonia

“…Band ogives consist of crescentshaped alternating dark and light bands. A dark band represents a mass of ice which has passed through an icefall or avalanched over a cliff during a summer season, thereby collecting detritus and dirts and forming layers of blue ice (e.g., King and Lewis, 1961;Reynaud, 1979). Since a light (winter ice) and dark (summer ice) ogive band is formed each year below an icefall or a cliff, the width of a pair indicates the amount of annual ice flow in a stable glacier (e.g., Haefeli, 1951;Lliboutry, 1957;Paterson, 1981).…”

21 years of British geomorphology

“…Lewis's last three publications were amongst the most important ever written in this field: on Norwegian cirque glaciers, published by the Royal Geographical Society (1960), on ogives (with C.A.M. King, 1961) and on glacier sideslip (with J.W. Glen, 1961).…”