Cryospheric systems - Fundamentals of the Physical Environment - page 367

(a) Erosive processes and glacier types (b) Erosional landforms

Peripheral mountains

Temperate ice
Alpine glaciers

Mountain glaciation

ice

Outlet glacier
Piedmont
lobe

Abrasion Abraded

ground

Scour-
'Knock & lochan'

Selective
quarrying

Breaching
-
troughs

Extensive
quarrying

Abrasion Scour

Z IV Z III Z II Z I Z II Z III Z IV

(c) Stratigraphy

(d) Sedimentary landforms

Ice

Till
Glaciofluvial
sediment
Bedrock

Till absent
or thin
veneer

Streamlined till
(drumlins etc)

Glaciofluvial
meltwater
deposits

Moraines

Figure 15.13 Glacier geomorphic landsystem zones. See text for explanation.
Source: After Addison (1983)

stress and pressure-melting, enabling the ice stream to
exploit weaker bedrock. Quarrying is self-enhancing, as
it draws more ice into the developing rock basin, and this
increases dramatically in the outlet glacier zone (Zone III).
In steady state the ELA is located relatively close to ice
sheet margins, nourished and melted in advection-driven
mass and energy balance conditions. This transforms the

ice stream into a temperate, warm-based state and
vigorous outflow draws down adjacent inland areas of the
ice sheet through outlet glacier troughs. They are the
most impressive of erosional landforms, excavated 1-5 km
deep and breached clean through any cordillera in their
path regardless of subglacial topography. Transfluent ice
flow on this scale excavated fjords through the coastal
mountains of southern Norway ( Plate 15.13 ), the South
Island of New Zealand, British Columbia, Alaska,
southern Chile and - to a lesser extent - western Scotland.
The Finger Lakes region south of Lake Ontario marks
transfluent ice flow towards the southern margin of the
Laurentide Ice Sheet. Beyond the constriction of outlet
glacier troughs, ice fans out in the piedmont zone (Zone
IV). Where ice flow is still vigorous it erodes knock-and-
lochan topography of parallel roches moutonnées inter-
spersed with shallow rock basins which become lake-
filled during deglaciation.

GLACIER DEPOSITIONAL
LANDSYSTEMS

Alpine depositional landsystems
Glacier confinement by rock walls also shapes and con-
strains deposition in the alpine environment. Supraglacial
debris derived from the rock walls is usually stacked in

Plate 15.13 A glacier-excavated rock wall towers 1 km
above an arm of Sognefjord, south-west Norway, continuing
for several hundred metres below water level.
Photo: Ken Addison