The Origin of Glacially Fluted Surfaces-Observations and Theory

Abstract

ABSTRACT. Studies of Ruted surfaces beyond the ma rgins of glac ie rs in Spitsberge n , I ce la nd , Norwa y a nd the Alps show that almost all emanate from rigid o bstructions, commonly boulders in till. Fi eld relations of Rutes are d escribed and it is shown that a rel a tionship exists b e tween Rute h eight and the h eight of the initiating obstruction. Subglacia l observations indi ca te that Rutes form wh en till is intruded into tunnels whi ch te nd to open up in the lee of obstacles . The pattern of stra in implied by this process is shown to be reRec ted by mi cro-a nd mac rofabri cs in the till . Th e commonly found occurrence of an ave rage spacing be tween Rutes d oes not arise b ecause of some rhythmic or periodi c m echanism in the gla cie r , but is produced by the rand om seeding of b o uld ers whi ch themselves generate Autes.It is sugges ted th a t the term Rute be used a s a g en eti c ra ther tha n a d esc riptive term, and b e res tricted to long p a ra llel-sided ridges whi ch re Aec t acc urately the direction of ice m ove ment and whi ch form wh en d eformabl e subgl ac ia l m a te rials are intrud ed into tunnels whi ch te nd to open up on the lee sides of single rigid o bstruc tio ns on the glac ier bed.RES UME. L 'arigine des surfaces glaciaires "cl fiules"-abservaliall s el Ih earie. D es etud es d e surfa ces cannelees en Autes au-dela des marges d es gl ac iers au Spitsb e rg, en Island e, en N o rveg e e t dans les Alpes, montrent que d e presque toutes emergent d es obstacles solides, d 'ordin a ires d es bl ocs d a ns la moraine. La d escription d e I'en vironn em ent d es Rutes montre qu ' il existe un e rela tion entre la h a uteur d e la Rute e t la hauteur d e I'obstacl e qui en es t I' origin e. D es obse rva tions sou s-gl acia ires indiqu e nt que les Rutes se form e nt lorsque la morain e s' e ngage da ns d es tunnel s qui tendent a s' ela rgir a I' ava l d e I'obsta cle. Le typ e d e contrainte mise en j eu par ce processus es t. m o nll'e-t-on, un reRe t d e la compos ition e n p e tits et gros elements d e la morain e. La consta ti o n courante d ' un esp acement moyen e ntre les Au les ne vi ent pas d e quelque m ecanism e rythmiquc ou pe ri odiqu e d a ns le gl ac ie r , m a is es t le produit d e la repa rtiti on a lealo ire d es blocs qui o nt engendres les Rules .On suggere d 'e mpl oyer le m o t AUl e comme un term e genetiqu e plut a l que desc riptif, e l d e le reserver a d es ri des a ll o ngees a bords p a ra ll eles qui reRe tenl fid elem ent la direc ti o n du m ou veme nt d e la gl ace et qui se forment lo rsque des ma te riaux sous-glacia ires deforma bl es s'engagent d a ns d es tunn els qui l" nd ent a s'ela rgir a I' aval d' o bsta cl es so lid es indi viduels sur le lil du gl ac ier. Z USAMM EN FASSU NG . Die H erkullf l glazial gerilller Oberfiiichen -Beobachlllllgell 1I11dThearie. SI udi en a n den gerillte n OberRachen ausse rha lb d el' Gl elsch e rra ndcr in Spilzbe rge n , Island , Norwege n lmd den Alpe n zeigen , d ass a ll e an starre Hind ...

Sculpted Bedrock Forms along the Niagara Escarpment, Niagara Peninsula, Ontario

“…In earlier literature (Hall, 1843;Lyell, 1845;Wright, 1889; and many others) the terms glacial grooves or glacial furrows correspond to the modern term p-forms, although Chamberlin (1888) uses the terms fluting and fluted hills. The positive relief features we describe are morphologically similar to till flutes as described by Boulton (1973), but as they cannot result from the same process we term our features remnant ridges or rat-tails (positive relief) and furrows (depressions, negative relief). The former correspond to the term tadpole rock {French: rocdrumlin) proposed by Dionne (1987).…”

δD-δ18O Relationships and the Thermal History of Basal Ice Near the margins of two Glaciers in Lyngen, North Norway

“…Where melted out in the glacier forefield, the fluted till layer is typically 0.3--{) .8 m thick but locally exceeds 1.5 m . The presence of the fluted till, generally believed to form under warm-based ice (Boulton, 1976), suggests that "Flutes Glacier" has a warm-based sector up-glacier from a cold-based margin . Estimates of basal ice temperatures using a modification of the Robin model (Robinson, 1984) support this inference.…”

Emergent drumlins and their clones: from till dilatancy to flow instabilities

“…12. (a) If pre-existing sediment contained structures, say thrusts or folds, these could be preserved in drumlin cores even though they have no process relationship to the drumlinization. (b) Flutes are much smaller landforms (tens of metres) than drumlins, and their common positioning in the lee of lodged boulders is usually taken to imply that they form by sediment migration into a pressure-lee or cavity behind the boulder (Boulton, 1976). An alternative is that they might be formed by flow instabilities whereby a thinning (by advection) till sheet with an unstable wavy surface becomes 'anchored' on boulders when they are encountered.…”

“…Positive elements of this relief have been classified and named according to their size and shape. Flutes are narrow and tens of metres in length (Boulton, 1976), drumlins are elliptically shaped hills, hundreds to a few thousands of metres long (Menzies, 1979), mega-scale glacial lineations (MSGL; Clark, 1993) are ridge-groove structures up to 100 km long, and ribbed or Rogen moraines are ridges transverse to flow, but are poorly named because they are not actually moraines. Subglacial ribs might be a better term for these latter features.…”