Movement of Water in Glaciers

Abstract

ABSTRACT. A ne twork of p assages situa ted along three-grain intersections enabl es water to p ercolate through temperate glacier ice. The d eformability of the ice a llows the passag es to expand and con tract in response to ch a nges in pressure, a nd melting o f the p assage walls by heat generated by viscous dissip a tion and ca rri ed b y above-freez ing water causes the larger passages gradually to in crease in size a t the expense of the sma ll er ones. Thus, th e behavior of the passages is prima rily the result o f three basic ch a racteristics: ( I) the capacity o f th e system continua ll y adj usts, though not instantly, to flu ctu ations in the suppl y o f melt water; (2) the direc tion of movement of the wa ter is d etermin ed mainly by the a mbient pressure in the ice, which in turn is governed primarily b y the slo pe of the ice surface a nd secondaril y b y the local topogra ph y of the glac ier bed ; and, most importan t, (3) th e ne twork of passages tends in tim e to become a rborescent, with a superglacia l part much like an ordin a r y river sys tem in a karst region , an englacial part com prised of Iree-like systems of passages penetrating th e ice from bed to surface, and a subglacia l p a r t consisting of tunn els in the ice carrying water a nd sedimen t a long the glacier b ed. These ch a rac teristics indica te that a sh ee t-like basa l water layer under a glacier wou ld normally be unstab le, th e stable form being tunnels: a nd they expl a in, among o ther things, why ice-marginal melt-water stream s and la kes a re so com mon , why eskers, which are generally considered to ha ve form ed in subglac ia l passages, trend in the general direction of ice fl ow with a tendency to follow va ll ey fl oors and to cross divides at their lowes t points, why they a re typicall y discontinuous where t hey cross ridge crests, why they sometimes con tain fragments from bedrock outcrops near the esker but no t actuall y crossed by it, a nd why they seem to be formed mostly during th e later stages of glaciation.RES UME. Ces ca ra cteristiques indiquen t qu 'u n n iveau d 'eau e tendu comme un drap su r le lit d ' un gl acier d evra it n orm a lement etre une formation insta ble, la form e stabl e e ta nt cell e d es tunnel s; ceci explique, en tre a utres, p ourquoi les torrents et lacs d 'eau d e fu sio n sont si communs le long d es ri ves d es glaciers, pourquoi les eskers, qui son t genera lement consideres comm e ayant e te formes par d es canaux sous-glaciaires, tend en t a s'aligner dans la direction genera le d e I'ecoul ement d e la glace avec une tendance a suivre le fond d e la vallee et a traverser les o bstacles en leur point le plus bas, pourquoi ils sont typiqu em ent interrom pus lo rsq u ' ils traversent la crete d'une ond ul a ti on, p ourquoi ils contien nen t parfois d es fragments pre leves sur le lit pres de I'esker mais non exactemen t sur sa trajectoire et pourquoi il s semblen t se former surtout a u cours des d erniers stades d 'un e glac iation. ZUSAMMENFASSUNG . B ew...

Subglacial hydrological connectivity within the Byrd Glacier catchment, East Antarctica

“…2a). Bed slope has only around one-tenth of the effect of ice-sheet surface slope on the flow of basal water (Shreve, 1972). Ice-surface gradients in Antarctica are generally low, however (Fig.…”

Ice-flow reorganization within the East Antarctic Ice Sheet deep interior

“…The catchment area was estimated by determining the hydrostatic potential gradient (Shreve 1972) of the South Pole region using surface (Jezek 1999;Fretwell et al 2013) and bed elevation models (Fretwell et al 2013), and defining the catchment as all grid cells from which subglacial water would eventually flow into the area of the SPL. Following a routing algorithm similar to Tarboton (1997) Q3 and starting at the lake grid cells, any adjacent grid cells with a hydrostatic potential gradient that pointed ±45°relative to the direct line between cell centres were included as part of the SPL catchment.…”

Subsurface hydrology of an overdeepened cirque glacier

“…2) was generated from the surface and basal elevation maps of Sanders and others (2010). Following Shreve (1972), hydraulic potential gradients were calculated assuming that basal water pressures are everywhere equal to the ice overburden pressure. While the true gradients will differ due to variations in basal conditions, this first-order approximation allowed identification of areas through which basal waters might be routed.…”

“…Lliboutry, 1971;Röthlisberger, 1972;Shreve, 1972;Iken and Bindschadler, 1986;Clarke, 1987;Flowers and Clarke, 2002;Bates and others, 2003). It is postulated that subsurface waters flow at the pmp, and that any excess heat gained from flow or geothermal sources is used to warm or melt the ice adjacent to the channel (Alley and others, 2003a;Clarke, 2005;Tweed and others, 2005).…”