Eyles 2015 (5) Flashcards
What does this paper talk about?
Research on deformation till and how it facilitates ice flow in the Saskatchewan Glacier in the Canadian Rockies and pervasive bed deformation under the glacier.
How big is the Saskatchewan Glacier (SG) in Banff National Park, Alberta, Canada?
Some 9 km in length and up to 2 km wide.
What is Boulton & Eyles’s (1979) definition of a ‘valley glacier landsystem’?
Where long- term preservation of primary glacial sediment (for example, till) is normally prohibited by reworking by powerful outwash rivers flowing along the confined valley floor and by steep valley-side bedrock slopes dominated by mass flow processes and the collapse of ice-cored lat- eral moraines.
What has played a major role in trapping sediment within the valley?
Unusually for valley glaciers, a large area of the former subglacial bed of Saskatchewan Glacier has been exposed by rapid retreat following the Little Ice Age.
The maximum downvalley LIA extent of Saskatchewan Glacier was reached in 1854 and this position occurs just up valley of a prominent rock bar.
Like most Cordilleran ice masses, Saskatchewan Glacier reached its maximum Neoglacial extent at…
the culmination of LIA cooling in the mid-Nineteenth Century (1854) and occupied this position until approximately 1900.
There are three distinct types of genetically related flute bedforms on the surface of the till bed exposed at Saskatchewan Glacier:
(i) boulder-initiated flutes
(ii) crevasse-initiated flutes
(iii) ice-pushed flutes and scours
What are majority (some 70%) of the flutes on the corrugated till plain?
Ice pushed flutes
What are boulder initiated flutes?
These flutes occur as a predominantly straight till ridge extending in a downglacier direction from a large boulder (or boulder cluster) partially embedded in the till surface.
They are parallel-sided, with sharply defined lateral margins.
What indicates the presence of boulder initiated flutes?
A white-coloured silt that accumulates in ephemeral ponds within the grooves and by the selective growth of vegetation.
What are crevasse related flutes?
Ridges that are not linear but very gently sinuous and which lack boulders at their heads.
The headward termination of crevasse- related flutes simply consists of a low swell in the till surface which, when traced downvalley, gradually changes into a distinct ridge.
These flutes not only lack headward boulders or lateral grooves but also have irregular crest lines with considerable variation in their height and width along their long axis.
What are ice-pushed flutes and scours?
They consist of a shallow flat-floored and linear scour <50 cm deep that terminates downvalley at a single large boulder lying within the termination of the scour.
Boulders are sub-angular in shape, show few striations and evidently have not undergone extended subglacial transport.
The cross-profile and width of the central groove reflect the size of the terminating boulder.
What are boulder-related flute ridges the product of?
Near surface till being deformed subglacially below the ice base and squeezed into an initial small subglacial cavity in the immediate lee of single or clustered boulders (nests) embedded in the till.
The embedded boulder and the initial lee-side ‘proto flute’ then act together as a larger distended obstacle; continued ice flow results in subsequent downglacier migration of the incipi- ent lee-side cavity which fills sequentially with deforming till, resulting in overall lengthening of the flute ridge.
What are crevasse related flutes the product of?
They are the subglacial ‘casts’ of radial crevasses in the ice margin. Unlike boulder-initiated flutes, crevasse-related flutes probably formed coevally along their length by subglacial ‘pressing’ of a soft, wet silt-rich substrate up into the base of open crevasses.
What are ice-pushed flutes the product of?
Deformation of the till substrate when a large boulder was pushed forward to form an arcuate frontal ‘bow wave’ of soft till.
Ploughing boulders are angular in shape and did not experience lengthy subglacial transport and abrasion, having originated as rock fall debris that was carried passively on the ice surface.
Large supraglacial boulders dumped on the emerging till surface from a thinning ice margin were bulldozed forward during winter readvances and acted as large ploughs under the ice.
