An experimental programme has been carried out for studying temperate-ice sliding over rock surfaces with a wide range of roughnesses, for normal and shear stresses comparable to those expected under real ice masses. The limiting static shear stress for acceleration has been found to be directly proportional to the normal load giving a constant limiting coefficient of static friction characteristic of the surface. For a constant applied normal stress N and shear stress τ b, well below the limiting static shear, a steady velocity Vb results which increases approximately proportionally to τ b and decreases with increasing N and the roughness of the surface. For high normal stress the velocity becomes approximately proportional to the shear stress cubed and inversely proportional to the normal stress. As the shear stress increases acceleration sets in, which, for different roughness and normal loads, tends to occur for a constant value of the product τ b Vb . For some surfaces at high normal loads this acceleration was retarded by erosion. For constant-applied-velocity tests a steady shear stress resulted, which tended to become constant with high velocities, and which increased with increasing normal stress but with a reduced coefficient of sliding friction. The relevance of the results to the sliding of real ice masses is discussed with particular reference to the importance of the effect of the relative normal stress, above basal water pressure, to the sliding rate.

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...

Heard Island, a heavily glacierized volcanic island in the Southern Ocean, is 80% ice-covered, with glaciers descending from 2,400 m to sea level: major glaciers are up to 7 km long with areas exceeding 10 km. Much of the island was photographed from the air in 1947 and again in early 1980. Photographs and limited ground surveys record changes (mostly retreats) in glacier fronts. Retreat is most marked on the eastern flanks where former tidewater glaciers are now grounded inland. Glaciers on northern and windward western flanks still end in ice cliffs but have narrowed; glaciers and ice caps on Laurens Peninsula (maximum elevation 710 m) are up to 65% smaller. Nearby lies Kerguelen and other southern islands with long climatic records have warrned significantly since the early 1960s. Surface and upper-air climatic data from Heard Island 1947–54 and records from automatic weather stations 1980–82 suggest that Heard too has warmed slightly, concurrently with a possible northward shift of low-pressure system tracks in this region. Temperatures have remained above average through the early 1980s and glacier retreat is expected to continue.

King George Island and Nelson Island, close together in the central South Shetland Islands, were discovered early in the 19th century and often visited by whalers and sealers. Whalers also used their harbours early in the present century. The first permanent station was established in 1947 by the Falkland Islands Dependencies Survey. Currently they are the site of scientific stations and depots operated by eight Antarctic Treaty nations (Argentina, Brazil, Britain, Chile, Peoples' Republic of China, Poland, USSR and Uruguay), all of which make use of their accessible harbours and relatively long summer season.

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