Geology Reference
In-Depth Information
Table 10.4—Cont'd
Formative process
Landform
Description
Ice-contact
deposition from
meltwater or in
lakes or both
Kame
Flat-topped deposit of stratified debris
Kame field
Large area covered with many individual kames
Kame plateau
Broad area of ice-contact sediments deposited next to a glacier but
not yet dissected
Kame terrace
Kame deposited by a stream flowing between the flank of a glacier
and the valley wall, left stranded on the hillside after the ice goes
Kame delta (delta
moraine)
Flat-topped, fan-shaped mound formed by meltwater coming from a
glacier snout or flank and discharging into a lake or the sea
Crevasse fill
Stratified debris carried into crevasses by supraglacial meltwater
Proglacial
Meltwater erosion
Scabland topography,
coulee, spillway
Meltwater features in front of a glacier snout. Water collected in
ice-marginal or proglacial lakes may overflow through spillways
Meltwater
deposition
Outwash plain or
sandur (plural sandar)
Plain formed of material derived wholly or partially from glacial
debris transported or reworked by meltwater and other streams.
Most sandar are composed wholly of outwash, but some contain
inwash as well
Valley train
Collection of coarse river-sediment and braided rivers occupying the
full width of a valley with mountains rising steep at either side
Braided outwash fan
Debris fan formed where rivers, constrained by valleys, disembogue
on to lowlands beyond a mountain range
Kettle (kettle hole, pond)
Bowl-shaped depression in glacial sediment left when a detached or
buried block of ice melts. Often contains a pond
Pitted plain
Outwash plain pitted with numerous kettle holes
Source:
Adapted from Hambrey (1994)
release of subglacial meltwater. Where the meltwater
is under pressure, the water may be forced uphill to
give a reversed gradient, as in the
Rinnen
of Denmark.
Subglacial gorges, which are often several metres wide
compared with tens of metres deep, are carved out of
solid bedrock.
Subglacial landforms
Channels
Some glacial landscapes contain a range of channels cut
into bedrock and soft sediments. The largest of these are
tunnel valleys
, such as those in East Anglia, England,
which are eroded into chalk and associated bedrock.
They can be 2-4 km wide, over 100 m deep, and
30-100 km long, and sediments - usually some com-
bination of silt, clay, gravel, and peat - often fill them
to varying depths. As to their formation, three mech-
anisms may explain these tunnels (Ó'Cofaigh 1996):
(1) the creep of deformable subglacial sediment into a
subglacial conduit, and the subsequent removal of this
material by meltwater; (2) subglacial meltwater erosion
during deglaciation; and (3) erosion by the catastrophic
Eskers
Eskers
are the chief landform created by subglacial melt-
water (Figure 10.7; Plate 10.14). Minor forms include
sediment-filled Nye channels and moulin kames, which
are somewhat fleeting piles of debris at the bottom of a
moulin
(a pothole in a glacier that may extend from the
surface to the glacier bed). Esker is an Irish word and is
now applied to long and winding ridges formed mostly
