Glacial systems operate similarly to viscous river systems by abrading and plucking sediment from a source area and transporting it to a depositional basin. Glaciers act as conveyor belts, moving large quantities of sediment. Factors like cold temperatures and precipitation are required for ice to accumulate and flow as glaciers. Glaciers essentially function as frozen drainage systems that transport water, sediment, and debris via internal shear and depositional processes from accumulation zones to terminus basins.

1. Glacial Systems
Glacial systems operate much like viscous fluvial systems. Sediment
is abraded and plucked from beneath in a source area and
transported to a depositional basin. Unless in a coastal setting, the
preservation potential for glacial deposits is low.

2. Conversion of Snow to Ice
If snow accumulates more rapidly
than it melts, over time it will undergo
a conversion to a dense ice that
resembles a metamorphic rock and is
capable of flow.

3. Plastic Deformation
To be considered a glacier,
ice must be thick enough
that it can flow under its
own weight.

4. Sediment Transport
Because of its high viscosity, ice is a highly competent agent of
erosion and sediment transport. Glaciers act as conveyor belts,
moving extremely large quantities of sediment from the source area
to the basin.

5. Controlling Factors
Cold temperatures and
significant precipitation are
both required to produce ice
of sufficient thickness to flow
as glaciers. Therefore,
glaciers are restricted to
areas of high latitude and/or
high altitude.

6. Mass Balance
Whether a glacier front advances or retreats is controlled by the relative balance
between precipitation in the zone of accumulation and melting in the zone of
ablation. These are separated by the snow line, which identifies the point where
these two factors are equal.

8. Frozen Drainage System
Glaciers are, in essence, a frozen drainage system. Water (snow/ice) and
sediment are collected primarily near the head and transported to a
depositional basin at the terminous.

9. Erosion
Weathering
(Frost Wedging)
Deposition
Transportation
Dominant Processes
Internal shear

10. Erosional
Features
Plucking extracts angular boulders leaving irregular depressions. Plucked boulders
and other materials become frozen into the glacier base and are drug over the
surface causing abrasion, which leaves striations and grooves.

11. Advancing Glacier Front
Actively advancing glaciers occur
when snow accumulates more
rapidly than it melts and are
characterized by steep, well-defined
fronts of relatively clean ice.

12. Retreating Glacier Front
Glacial retreat occurs when melting
occurs more rapidly than snow
accumulates and is characterized
by gentle, poorly-defined fronts ,
potentially covered by debris, lakes,
and vegetation.

13. 1957 1980

14. Simplified Model
As glaciers advance and retreat, they create a wide and complex variety
of depositional facies.

15. Continental Glacial Deposits

16. Till
Because of the high viscosity of
ice, glaciers transport all sizes
of sediment from clay to very
large boulders. This sediment
is all deposited together in
morraines as till.

18. Ground Morraine
If more material accumulates beneath the glacier than can be transported, it is
deposited as a ground morraine, consisting of irregular mounds of sediment.
Upon melting numerous small, nonconnected lakes tend to form.

25. Eratics
Materials can be transported long distances by ice, depositing sediment
that does not match the surrounding rock units.

27. Eskers
Water flows in tunnels beneath the ice as subglacial
streams, carrying large quantities of sediment.
Upon melting, the sediment is deposited upon the
surface.

28. Outwash Delta
Esker

30. Outwash
As the ice melts, water and sediment are transported away from the glacier front.
Because of the high volume and large size of sediment, outwash streams tend to
be braided. Also referred to as glaciofluvial or fluvioglacial deposits.

31. Glacial Map of
North America