Empirical Studies of Ice Sliding

Abstract

A BSTRACT. An experimental progra mme has been carried out for studying te mperate-i ce sliding over r ock surfaces with a wide ra nge of r oughnesses, for n ormal and shear stresses comparable to those expected und er real ice masses. The limiting stati c shear stress for acceleration has been found to be directly proporti onal to the normal load giving a constant limiting coeffici e nt of stat ic fri ctio n characteristic of the surface.Fo r a consta nt applied normal stress N and shear stress Tb, well below the limiting static shear, a steady velocity Vb results whi ch increases a pproxima tely proportionally to Tb and d ecr eases with in creas ing Nand the roughness of the surface. For high norma l stress the veloc ity becomes a pproximately proportiona l to the shear stress cubed and inversely prop o rtio na l to the normal stress . As the shea r stress increases a ccele ra tion sets in, whi ch, for different roughn ess a nd norm al loads, te nds to occur for a co nsta nt value of the produ ct Tb Vb. F o r some surfaces at high norm al loads this acceleration was reta rded by erosio n. For consta nt-a ppliedvelocity tests a steady shear stress res ulted, which tend ed to become co nsta nt with hig h velocities, a nd whi ch in creased with increa sing norma l stress but w ith a redu ced coeffi cient of sliding fri ction. The rel evan ce of the results to the sliding of real ice m asses is discussed with particula r referen ce to the importa nce of the effect of the rel ati ve no rmal stress, a bove b asal water pressure, to the sliding ra te.R ESUME. E ludes empiriques du glissemen t de la glace. On a mis a u point un progra mme experi menta l pour e tudier la gl ace te mpe ree est so n glisse m e nt sur des surfaces r ocheuses de ru gos ite varian t d a ns d e g ra ndes proportions, pour d es etTorts norm a ux o u un cisa illeme nt compa rables a ceu x qu e l'on peut a tte indre d a ns d es masses reell es d e glace. On a trou ve que la contra inte d e cisa ill ement sta tiqu e limite pou r a boutir a u ne acceleration est directe ment proporti o nn ell e a la cha rge n o rm a le ce qui donn e un e valeur limi te constante du coeffi cient d e fri ction stati que qui est un e ca racteristique d ' u ne surface. P o ur un effort norma l co nsta nt Net une co ntra inte d e cisa ill ement Tb , bie n inferieure a u c isa illemen t sta tiqu e limite, une vitesse d 'equilibre V b s'eta blit qui cro it a pprox ima ti vem e nt co mm e T b et d en'o it qua nd croisse nt N e t la rugosit e de la surface. P o ur un effort n o rm a l importa nt la v itesse dev ient approximat ivement propo r t io nn ell e au cube du cisaill ement et in verse m e nt proportionn ell e a l'effo rt norma l. Lorsque le cisaill ement c ro it, l' accelerati on commence qui, pour d iffe re ntes rugosites, et diffe re ntes charges no rm ales tend a ma inte nir co nsta nt le p roduit T b V b. Pour certa ines surfaces a fortes cha rges no rm a les, cette accelera tion est reta rd ee par l'eros ion. P our d es essa is it vitesse co nsta nte, on obti...

The Robustness of One-Dimensional, Time-Dependent, Ice-Flow Models: A Case Study from Storglaciaren, Northern Sweden

“…Model centerline surface velocities for the f'=3.5*10-9 case are of similar magnitude as those observed, but their distribution does not match the observed record (Pohjola 1996) in detail (Fig. This value deviates slightly from those given in the literature for Storglaciaren (Hanson 1995) or other glaciers (e.g., Budd et al 1979). Instead, the centerline surface velocity distribution shows a characteristic double-peak centered around grid point 11 that mirrors the width distribution (not shown) along the centerline, hence, appears to be a geometric Geografiska Annaler * 78 A (1996) Table 2.…”

Continental scale, high order, high spatial resolution, ice sheet modeling using the Ice Sheet System Model (ISSM)

“…Friction is applied at the ice‐bedrock interface. The basal drag follows an empirical relationship presented by Paterson [1994] and first calibrated by Budd et al [1979], written in a viscous‐type law of friction: where v b is the basal velocity vector tangential to the glacier base plane, τ b the tangential component of the external force σ · n , and α 2 a positive constant (i.e., stress opposes ice motion). Paterson [1994], usually includes the effective pressure in the basal friction law, to account for the presence of water lubricating the ice‐bedrock interface.…”

The Response Time of Glacial Erosion

“…f d and f s are the flow parameters for deformation and sliding, respectively, and n is the Glen flow law exponent, which is often assumed equal to 3. Here the flow parameters are taken from Oerlemans () who used values from Budd et al (). In Table , we summarize the values of the main variables that are used in the following sections.…”