EFFECTS OF GLACIATION
Although the last glacial period ended more than 8,000 years
ago, its effects can still be felt today.
For example, the moving ice carved out the landscape in
- Tills - unstratified glacial drift consisting of clay, sand, gravel, and boulders intermingled
- Drumlins - an elongate or oval hill of glacial drift
- Eskers - a long narrow ridge or mound of sand, gravel, and boulders deposited by a stream flowing on, within, or beneath a stagnant glacier
- Fjords - a narrow inlet of the sea between cliffs or steep slopes
- Moraines - accumulation of rock debris (till) carried or
deposited by a glacier. The material, which ranges in size from blocks or
boulders (usually faceted or striated) to sand and clay, is unstratified
when dropped by the glacier and shows no sorting or bedding. Several kinds
of moraines are recognized:
- Cirques - a deep steep-walled basin on a mountain usually forming the blunt end of a valley
·
Horns - flanks. Headward erosion
of these cirques finally leaves only a sharp peak flanked by nearly vertical
headwall cliffs, which are separated by arêtes. Such glacially eroded mountains
are termed horns, the most widely known of which is the
The weight of the ice sheets was so great
that they deformed the Earth’s crust and mantle. After the ice sheets melted, the ice-covered
land rebounded. Due to the high viscosity
of the Earth, the flow of mantle rocks which controls the rebound process is
very slow – at a rate of about 1 cm/year near the center of rebound today.
During glaciation, water was taken from
the oceans to form the ice at high latitudes, thus global sea level dropped by
about 120 meters, exposing the continental shelves and forming land- bridges
between land-masses for animals to migrate.
During deglaciation, the melted ice-water returned to the oceans,
causing sea level to rise. This process
can cause sudden shifts in coastlines and hydration systems resulting in newly
submerged lands, emerging lands, collapsed ice dams resulting in salination of
lakes, new ice dams creating vast areas of freshwater, and a general alteration
in regional weather patterns on a large but temporary scale. It can even cause temporary
reglaciation. This type of chaotic
pattern of rapidly changing land, ice saltwater and freshwater has been
proposed as the likely model for the Baltic and Scandinavian regions, as well
as much of central North America at the end of the last glacial maximum, with
the present-day coastlines only being achieved in the last few millennia of
prehistory. Also, the effect of
elevation on Scandinavia submerged a vast continental plain that had existed
under much of what is now the North Sea, connecting the British Isles to
continental
The redistribution of ice-water on the
surface of the Earth and the flow of mantle rocks causes changes in the
gravitational field as well as changes to the distribution of the moment of
inertia of the Earth. These changes to
the moment of inertia result in a change in the angular velocity, axis, and
wobble of the Earth’s rotation (Post-glacial rebound). The weight of the redistributed surface mass
loaded the lithosphere, caused it to flexure and also induced stress within the
Earth. The presence of the glaciers
generally suppressed the movement of faults below (Johnston 1989, Wu &
Hasegawa 1996, Turpeinen et al. 2008).
However, during deglaciation, the faults experience accelerated slip,
and earthquakes are triggered (Post-glacial rebound). Earthquakes triggered near the ice margin may
in turn accelerate ice calving and may account for the Heinrich events (Hunt
& Malin 1998). As more ice is
removed near the ice margin, more intraplate earthquakes are induced and this
positive feedback may explain the fast collapse of ice sheets.
