Environmental Engineering Reference
In-Depth Information
around 16ยท7 ka BP, triggering rapid final deglaciation of the dwindling British ice sheet
(Figure 1c).
Plate 15.9
Ice-cored end moraines, showing parallel thrust
structures, marking a recent retreat position of the eastern
margin of the Greenland ice cap, now off to the right.
Photo: Ken Addison.
landforms. Later ice advances obscure or obliterate earlier landforms where there is a
sequence of glacial stages. Within a single stage, or glacial event, ice sheet growth at
glacial maximum may occur between more localized alpine glaciation phases, with the
superimposition of landforms in areas common to both.
ALPINE EROSIONAL LANDSYSTEMS
Alpine glaciers tend to excavate linear
troughs
fed by inline and lateral tributary
cirques
.
Glaciation commences as regional snowlines fall far enough below mountain summits for
sufficient accumulation to generate ice flow. Tributary stream valleys and other sites
sheltered from prevailing winds and insolation, enlarged through
nivation
(see Chapter
25), are the first to collect snowbeds. Steep mountain slopes, high precipitation and
isothermal warm-based ice combine to generate rapid glacier outflow, which enlarges and
