Glacial Environment
General Information line occurs at lower altitudes. Large ice masses are
known as glaciers. Such ice masses exist because
Glacial environment is not widespread on the earth's over long periods the. snow and ice have been added
surface today. However, a widespread record of faster in a given ar~a than ice is lost by various
glacial activity during the Pleistocene ice age has processes. Glaciers have been defined as masses of
been left behind over vast areas, and a detailed study ice which, under the influence of gravity, flow out
of them has been most helpful in understanding the from the snow fields where they originate (HOLMES,
glacial processes and the characteristics of glacial 1965). A glacier consists of recrystallized and
deposits. This knowledge can be successfully applied compacted snow, melt water, and some rock debris.
in the study of ancient, e. g., pre-Pleistocene glacial The precipitation above snow line is in the form
deposits. Today, the glacial environment is restricted of snow. The loose snow is transformed into more
to areas around the north and south poles, and high compacted ice under pressure caused by loading of
mountains in other latitudes covered by snow e.g., new snow. The air is squeezed out. Glacial ice is an
the Alps and the Himalayas. aggregate of interlocking grains. A thin film of water
Glacial environments are characterized by the is present between the ice grains and plays an
dominance of ice as a geological agent. Accumulat- important role in the movement of glacier.
ion of ice is a result of low temperature combined
with high rates of precipitation and extremely low
rates of evaporation. Local and occasional presence
of ice cannot be regarded as evidence of glacial Geomorphology of Glaciers
environment. In temperate climates during winter
months activity of ice can be rather important, and Glaciers creep slowly downward and extend as
it may influence the sedimentationpatterns. Ice may tongue-shaped bodies of ice. Normally, glaciers are
cause some transport of material when packed in fed by the addition of new snow. All processes by
ice blocks, or when ice blocks strand on a sediment which a glacier gains ice are called accumulation. In
surface they may produce various types of deform- the lower reaches glaciers lose ice by melting,
ation structures in the underlying sediments. In evaporation, and calving of icebergs. The processes
German tidal flats effect of ice on the sedimentation are collectively known as ablation. The balance
process is sometimes very significant. However, in between these two processes-accumulation and
such regions principal sedimentation is not controll- ablation -characterizes a given glacier. Glaciers
ed by the activity of ice. The same is true of the rivers advance up to a point where ablation is balanced
of such climates. In this chapter we shall discuss with accumulation. If conditions change and
sedimentation in areas occupied by ice masses and ablation dominates, the glacier does not reach as far.
areas around such region : glacio-fluvial. The glacier is said to be retreating. If accumulation
Permanent ice masses exist above the snow line, dominates due to heavy snowfall, the glacier
which is the level up to which the snow melts in the advances farther down, and is said to be advancing.
summer. The occurrance of the snow line in altitude Near the lower end of a glacier-the snout-the
varies with latitude. In higher latitudes the snow thickness of ice is considerably less. Fig. 240 shows a
ACCUM UL ATIO N
F I RN LI M1T
AB LATION
Hor zon101 la ylt r ing
SU RFACE MORAI NE
I
Fig. 240. Schematic longitudinal profile across
GROUND MORAI NE a valley glacier showing main geomorphologic-
al fea tures. (Modified after STREIFF-BECKER,
_._ . - . - LINE OF MAXIMUM FLOW VELOCITY 1952 and SCHW ARZBACH, 1964)
H.-E. Reineck et al., Depositional Sedimentary Environments
© Springer-Verlag Berlin · Heidelberg 1973
Geomorphology of Glaciers 165
longitudinal section across a valley glacier to It may be, for example, that much pebble and boulder
demonstrate the relative importance of ablation and size sediment is mixed with sandy or muddy sediment
accumulation in various parts of a glacier. of a given region, and sediments of glacial-marine
Near the snout, detrital sediment is dumped due origin are formed.
to melting ice. Ifa glacier ends up in a water body (a A characteristic feature of most glaciers is the
sea or a lake), sediment is dumped into the water presence of crevasses and other deformation
body and is partly reworked by waves and currents. features in the ice surface. This is mainly due to the
However, if a glacier ends up in a sea deep enough to fact that the outer crust of a glacier behaves more as
permit the ice to float, a huge amount of ice is lost by an elastic solid than as a rheid. Reasons for the
the process of calving. Huge blocks of ice-ice- formation of crevasses may be varied; e.g., glacial
bergs-float away from the glacier. Icebergs usually flow, change in the path of the flow perhaps because
contain much entrapped sediment, and may trans- of a constriction of the path, widening of the path,
port glacial sediment over large distances before or glacier passing around a bend. Depending upon
they are melted. Such glacial-borne sediment their position, crevasses are named marginal
becomes incorporated in normal marine sediments. crevasses, transverse crevasses, longitudinal cre-
vasses, etc. Fig.241 and 242 illustrate different
types of crevasses.
The classification of glaciers is a difficult
problem. HOLMES (1965) recognizes following three
basic types of glaciers:
1. Valley Glaciers. Valley glaciers are ice masses
A MARGINA L CREVASSES B. TRANSVERSE CREVASSES
confined within valley walls of a mountain. Thick-
I
11 -
• NEW LY FORMED
OLO ROTATED
ness of ice can be several hundred meters. Valley
glaciers are usually fed by cirques and ice fields
located higher up. Examples: Rhone Glacier, Alps;
Gangotri Glacier, Himalayas.
2. Piedmont Glaciers. Piedmont glaciers are sheets
GlAC IAL
5 OUT - 1--- -= of ice formed by the coalescence of several valley
glaciers, which spread out beyond their valleys into
a lowland area. Example: Malaspina glacier of the
C. SPLAY ING AND o RADIAL SPLAYING coastal plain of southeastern Alaska.
LONGIT UDINAL CREVASSES AT SNOU T 3. Ice Sheetsor Ice Caps. Ice sheets are huge masses
Fig. 241. Scheme showing various types of crevasses in a glacier. of ice spreading over large continental or plateau
(Modified after SHARP, 1960) areas. Such masses occur in regions where the snow
Fig. 242. Photograph of a valley glacier show-
ing various types of crevasses. SC-splaying
crevasses, TC-transverse crevasses, MC-
marginal crevasses, TTC-tick-tack-toe cre-
vasse pattern, FE-firn edge, a-faint
ogives. (After SHARP, 1960)
