Snow, Ice, Avalanches, and Glaciers - Mountain Geography: Physical and Human Dimensions - page 192

FIGURE 4.35 A graph showing glacier retreat based on many mass balance studies. (National Snow
and Ice Data Center data. Redrawn courtesy of L. R. Dexter and K. Birkeland.)
Glacial Movement
The first recorded observation that glaciers may flow can be attributed to the Icelander
Sveinn Pálsson in 1794. In that year he climbed Öræfajökull and, looking down onto one
of its outlet glaciers, observed the prominent arcuate bands that have since come to be
known as ogives (see below). This prompted him to the remarkable observation for the
time “that glacier ice, without actually melting, has some kind of fluidity, like several
resins” (translated by Williams and Sigurðsson, 2004: 68).
Glacial movement is determined by the thickness of the ice, its temperature, the
steepness of its surface slope, the condition at the bed (frozen or thawed), and the con-
figuration of the underlying and confining topography. When the thickness of the ice
exceeds about 60 m (197 ft), internal deformation can occur and the glacier can move
(Sharp 1988). In general, the fastest movement occurs in the center of the glacier and
decreases toward the margins and frontal zone. Movement is also fastest at the surface
and decreases with depth, except where rapid sliding over the bed becomes a signi-
ficant component of total flow. On a longitudinal basis, movement is greatest near the
center at the equilibrium line and least at the head and terminus. The area above the
equilibrium line is the zone of accumulation; the area below is the zone of ablation (Fig.
4.31). Therefore, if a glacier is to maintain its form and profile, transfer of mass must
be greatest in this zone (Paterson 1994). Movement in the accumulation area is gen-
erally greatest in winter, because of increased snow load, while movement in the abla-