Showing papers in "Journal of Glaciology in 1965"

The flow of a glacier in a channel of rectangular, elliptic or parabolic cross-section

Abstract: Numerical solutions are found for the steady rectilinear flow of ice, obeying Glen’s non-linear flow law, down uniform cylindrical channels of rectangular, semi-elliptic and parabolic cross-section. The results are also directly applicable to the pumping of a non-Newtonian fluid down a pipe. There is assumed to be no slip of the ice on the channel surface. Certain results on the centre-line velocity in symmetrical channels may be derived purely from dimensional and symmetry principles. An analytical solution due to Dr. W. Chester is given for a semi-elliptic channel section which departs only slightly from a semi-circle. Contrary to a view sometimes held, the maximum shear stress at the ice surface in a parabolic channel and in some elliptical channels does not always occur at the edge. With the flow law, strain-rate proportional to (stress)3, the velocity averaged across the ice surface, which is easily measured with a line of stakes, is close to the average velocity over the whole section for a wide range of parabolic sections; the hydrological importance of this result is that the discharge may be inferred without the need to measure the velocity at depth. Arguments are given to show that the result still holds when there is slipping on the bed and when the power in the flow law differs somewhat from 3, Depending on the amount of bed slip and the shape of the channel section, the kinematic wave velocity for a range of parabolic channels is between 2.0 and 2.3 times the centre-line velocity of the ice, and between 2.0 and 3.5 times the mean surface velocity of the ice.

Dielectric properties of ice and snow-A review

Abstract: The permittivity and loss tangent of naturally occurring ice and snow are considered. The direct-current conductivity is considered only when it is of importance to the alternating-current and radio-frequency properties. Laboratory measurements on pure ice, and deliberately contaminated ice, are included to help in explaining and extrapolating the behaviour of natural ice and snow. The lower band of frequencies from 10 c./sec. to 1 Mc./sec. is occupied by a relaxation spectrum in which the relative permittivity falls from approximately 100 to 3. The loss tangent reaches a maximum at a frequency which varies from 50 c./sec. to 50 kc./sec. as the temperature increases from −60°C. to 0°C. We are interested in the effect of snow density, impurities, stress, crystal size, and orientation. For frequencies much greater than 1 Mc./sec., the relative permittivity is 3.17±0.07. The loss tangent reaches a minimum value at approximately 1,000 Mc./sec. beyond which the dominant influence is infrared absorption. The minimum is 10−3 at 0°C or 2×10−5 at −60°C. These values are greatly increased by impurities or free water. Some possible applications to glaciological field measurements are mentioned.

Photo-Interpretation of two Types of Rock Glacier in the Colorado Front Range, U.S.A.

Abstract: Two types of rock glacier occur in the Colorad o Front Ra nge. R ock glac iers on the floors of m od ern cirques closely resemble the tongues of sma ll valley g laciers. Because they contain cores of banded g lacia l ice a nd grad e up·valley in to latera l mora ines, rock g laciers of this type a re believed to represent the d ebris·covered tongues of former glaciers. M os t consist of two or more superimposed lobes, bounded by longitudinal furrows, a nd resulting from independent ice a d vances. Despi te their compound na ture, the complexes now a ppear to be moving d own-slope as single units . T wo genera tions of \"cirque-f1oor\" rock glaciers, both tentatively da ted as being of post-Pleistocene age, occur in the F ront R a nge. R ock glaciers of a n entirely different character occur beneath steep valley wa lls, w here they are supplied with debris by avalanche couloirs. Interstitial ice, responsible for the movem en t of \"valley-wall\" rock glaciers, probab ly results from the m etam orp hism of snow buried beneath rock-fa ll debris or supplied by winter avalanching. R EsUME. Photo-interpretat ion de deux types de glacier roclzeux dans le Colorado Front R ange, U.s. A . Deux types de glacier rocheux existent da ns le Colorado Front R ange. Des g laciers rocheux it la surface d e cirques modernes rassemblen t les la ng ues de petits glaciers d e vallee. Pa rce qu' ils contiennent des noyau x d e glace stra tifiee de glacier et s'avancent en amont da ns d es m oraines latera les, ces glaciers rocheux sem blent representer les la ngues couvertes d e d ebris d 'anciens glac iers. Ils consisten t pour la plupart en d eux o u plus de lobes sUl'imposes, limites pa r d es sillons longi tudina ux et resulta nt d 'avances independa ntes d e la glace. Malgre leur nature composee, les complexes appra issent maintenant se m o uvoir vel's I'aval com me d es unites isolees. D eux generations de glaciers rocheux de fond d e cirque, les deux estimes de l'age post-pleistocene, ex istent da ns le Fron t R ange. D es glaciers rocheux d'un caractere entierement differen t existent au bas de fa la ises de vallee, d'ou ils sont a limentes pa r les d ebris des couloirs d 'avala nche. La glace intersti tielle, responsable du mouvemen t des glaciers rocheux d e fa la ises de vallee, resul te proba blemen t d u metamorphisme d e la neige enterree sous les de br is ou a limentee p a r les avalanches d ' hiver. Z USAMMENFASSUNG. Plzotoill terpretation von zwei B lockgletsclzertypen in del' Colorado Front R ange, U.S.A. I n del' Colorado Front R a nge treten zwei Typen von Blockgletschern a uf. Blockgletscher a uf dem Boden von jungen K a ren ha ben ganz d as Aussehen von klc inen T algletschern . Da sie Kerne von geba ndertem Gletschereis entha lten und tala ufwa rts von Seitenmora ncn f1 ankiert sind, werden Blockgletscher d ieses Typs a ls A bbilder d el' schuttbedeckten Zungen fruher G letscher betrachtet. M eist bestehen sie a us zwei oder mehr ubereinanderliegenden Loben, die durch La ngsfurchen begrenzt sind und von una bha ngigen Eisvorstiissen herruhren . T rotz ihrer scharfen T rennung scheinen sich die Gebilde j etz t a ls geschlossene E inheiten a bwa rts zu bewegen. In der Front R a nge kommen zwei Generationen von \" K a rbod en\" -Blockgletschern vor, die beide versuchsweise a ls nach-pleistozan datiert werden. Blockgletscher ganz a nderen Cha rakters treten unter stcien T a lwanden a uf, a us d enen sie uber Lawinenbahnen mit Schutt versorgt werden. Eis in Zwischenra umen, das d ie Bewegung solcher \" T a lwand\" Blockgletscher verursacht, ist vermutlich durch U mbildung von Schnee en tsta nden, del' unter den herabsturzenden Schu ttmassen begra ben od er durch winterli che Lawinen a ngel iefert wird.

A numerical method of inferring the budget history of a glacier from its advance and retreat

Abstract: The paper considers how to calculate the budget history of a glacier from the historical record of its advance and retreat. The linearized differential equations developed in previous papers are used to compute a series of coefficients g(n). The g(n) operate directly on a record of annually spaced observations of the position of the glacier terminus, to give the time variation of net budget. The g(n) are calculated for South Cascade Glacier, Washington, U.S.A. and for Storglaciaren, Kebnekaise, Sweden, and are applied to the terminus records of these two glaciers. The results indicate that the figures for the retreat during individual years are not sufficiently reliable to deduce annual net budget changes with confidence. But the coarser features of the terminus records give net budget figures that agree well with the 9 yr. or 10 yr. means of recent observations. The theory extends the generalized budget record of Storglaciaren back by several decades. and shows an increase in net budget in the 1930’s that is not immediately apparent in the terminus record.

Net Budget and Flow of South Cascade Glacier, Washington

Abstract: Ice velocity, net mass budget and surface elevation change data were collected over the length and width of a small (3.4 km. long) valley glacier from 1957 to 1964. Ice velocities range up to about 20 m./yr.; three prominent velocity maxima along the length of the glacier correspond to maxima in surface slope. Net mass budgets averaged over the glacier surface range between − 3.3 m. of water equivalent (1957–58) and +1.2 m. (1963–64). Except for the year 1960–61, curves of net budget versus altitude are parallel. During the period 1958–61 the glacier became thinner at a rate averaging 0.93 m./yr. The net budget and thinning data are internally consistent. Relations between emergence velocity, net budget and surface elevation change are examined at four specific points on the glacier surface and as functions of distance along the length of the glacier. Emergence velocity averages about −0.5 m. in the upper part of the glacier and about +1.0 m. in the lower part. Ice discharge and ice thickness are also calculated as functions of distance. The discharge reaches a peak of 8.8 × 105 m.3 of ice per year 2.2 km. from the head of the glacier. The mean thickness of the glacier is about 83 m. A steady-state distribution of net budget is used to calculate a steady-state discharge, which is 2.2 times larger than the present discharge.

The Frequency Response of Glaciers

Abstract: The theory developed in previous papers to represent the response of a glacier to changes in the rate of accumulation and ablation has been used for a number of applications. A method of integrating the differential equations for a fixed frequency was programmed for a high-speed digital computer. This provides a better way of finding the frequency response than the earlier method which used series approximations or high and low frequencies. Results are given for (a) an artificial glacier showing varying amounts of diffusion of the kinematic waves, (b) South Cascade Glacier, Washington, U.S.A., as a check on previous results, and (c) Storglaciaren, Kebrekaise, Sweden. The response curves of Storglaciaren are very similar in shape In those of South Cascade Glacier but, since. Storglaciaren moves more slowly, the curves are shifted in frequency (by a factor of two). The phase of the response at the terminus of Storglaciaren plotted against frequency shows a double peak. Certain mathematical results for the artificial case of no diffusion are given in an Appendix. A computer programme was also written for calculating λ and μ coefficients and applied to South Cascade Glacier and Storglaciaren.

On the relationship of snow accumulation to surface topography at "Byrd Station", Antarctica

Abstract: R ecent measurements of snow accumulation on undulating surfaces around " Byrd station " , Antarctica indicate that the undulations a r e tending to be filled in. These resu lts are discussed in the light of current knowledge of the orig in and migration of such features. STEPPED surfaces and undulations of wavelengths of 5- 30 km. are now known to characterize much of the surface of the Greenland a nd Antarctic I ce Sheets, particularl y the latter, and there has been some speculation as to how these features might form. Nye ( 1959) for example would attribute surface waves of these dimensions (mea n amplitudes of about 20 m.) to irregularities in the underlying bedrock, but Bader ( 1961) believes that drifting snow is responsible for the formation of wavy surfaces in the high interior of Greenland. A fairly considerable surface relief is to be observed in the general area of new " Byrd station" , Antarctica. New " Byrd station " was constructed under the snow near the bottom of a broad depression and between it and the old " Byrd sta tion" located 10 km. to the west there are two smaller valleys. An examination of the surface in February 1 962 indicated that the valleys were accumulating much m ore snow than the crests of these undulations. In order to obtain some quantitative data on this r elationship between accumulation a nd surface topography, two stake lines were set up, one oriented pa ra llel to the prevailing wind direction and the other normal to it. The " east- west" line, (Fig. I ) comprising 21 stakes emplaced at intervals of 0·5 km. extended from the south-east corner o f the stake farm at o ld " Byrd" to a point about a kilometer north of the radio noise tower at new " Byrd station". The second line of 22 stakes was begun just to the east of the V.L.F. antenna and extended d own-wind in a southerly direction for a distance of 10·5 km. The elevati on at each stake was measured barometrically. In Figures 1 and 2 these elevations have been conve rted to absolute values based on the elevation at the gravity pier at new "Byrd station". As indicated in Figure I , the "east- west" line traversed two small valleys superimposed on a surface that sloped upward to the east. The relief along the " north- south " line of stakes (Fig. 2) differed somewhat in that it took the form of a fa irly steeply sloping surface intersected by two small steps. The impress ion gained in the field was that the " north- south" stakes traversed a major structural feature of the surface a nd that the undulations a long the "east­ wes t" line were superimposed upon this structure. However , it is diffi cult to say from obser­ vations over such a limited area of the surface whether or n ot the undulations are oriented in any particular direction. Nevertheless, a fter just three years o f observations the stake measure­ ments have yielded some interesting data. First, the pattern and magnitude of accumulation for the three years ending 30 January 1963, 30 January 1964 and 9 January 1965 are remarkably similar. Along the "east- west"

New light on the mode of uplift of the fish and fossiliferous moraines of the McMurdo Ice Shelf, Antarctica

Abstract: : The McMurdo Ice Shelf and associated faunal remains were examined in the vicinity of the easternmost Dailey Island. Stratigraphic, petrographic, and chemical composition studies of cores from 2 holes drilled through the ice shelf show that at these locations the shelf is composed only of fresh water ice. Although cores from the deeper hole possessed glacial textures throughout, much of the ice from this part of the McMurdo Ice Shelf may have been formed from the freezing of a layer of fresh water found sandwiched between the shelf bottom and the underlying sea water. The existence of fresh water under the ice shelf can most probably be attributed to drainage of surface melt water during the ablation season. There was no evidence to indicate that this part of the ice shelf is being nourished by the growth of sea ice onto its lower surface. The fish remains found on the ice surfaces were confined to a narrow zone along the tide crack and are believed to have been left in this vicinity by deep diving seals. The marine invertebrate remains on top of the ice are associated with morainal material and are believed to have been incorporated into the ice at the time of formation of the moraines. (Author)

Experimental study of non-basal dislocations in ice crystals

Abstract: AnSTRACT. Structures produced by chemical etching on the basal plane of ice c rystals have been studied a nd a re discussed in terms of non-basal g lide features. Slip bands, revealed by pa rallel rows of e tch pits, generally result from a rapidly applied stress. Etch channels were observed relative ly rarely in these exp eriments ; they can be inte rpreted as trails of dislocations moving slowly under the act ion of local st resses, sometimes to stresses produced during the e tching process. Features of the channels indicate that the dislocations emerging on the basal plane a re screw dislocations ; their Burgers vecto r was considered by previous authors to b e in the direction < I 123 ) , g liding on {I 122} and {101 o} slip p la nes. This assumption is inconsistent with the changes of channel direc tion we observed , for wh ich the {Olll } a nd {2421} slip plan es would have to be considered. As a simpler hypothesis the g lide system <000 1) , { IOIO} and ( 0001 ) , { l 120} is proposed.

Recent Changes in the Glaciers of Svartisen

Abstract: The history of glaciological studies in the Svartisen area is outlined, and observations made by earlier workers are summarized. The present position of the ice limit in the area is indicated and is compared with those of the past Evidence of extensive, and almost continuous, retreat of the glaciers is presented, and emphasis is placed on the rapidity of the changes since the 1930’s. In the present century, the formation of marginal lakes and the detachment of glacier tongues have characterized the decay of many of the Svartisen outlets.

The Genesis of the McMurdo Ice Shelf, Antarctica

Abstract: The recent discovery (Gow and others, 1965) ofa layer of fresh water under the McMurdo Ice Shelf invites a reconsideration of the early theory of its genesis. A general d escription of the area is given to record the wide area in which marine bottom deposits overlie freshwater ice. REsUME. La genese du McMurdo Ice Shelf. La decouverte recente (Gow and others, 1965) d'une strate d 'eau douce sous le M cMurdo Ice Shelf, invite a reconsiderer la theorie de sa genese. U ne description generale de la zone est donnee pour preciser la large partie Oll d es d epots marins d e fond se trouvent a la surface de glace d 'eau douce. ZUSAMMENFASSUNG. Die Entstehung des McMurdo-Ice-Shelf's, Antarktika. Die jilngste Entdeckung (Gow and others, 1965) e iner Schicht von Silsswasser unter d em McMurdo Ice Shelf gibt Anlass zu einer. Uberprilfung der frilheren Theoric seiner Entstehung. Eine allgemeinc Beschreibung des Gebietes gibt c ine Ubcrsi cht ilber den wciten Bereich, in dem Ablagerungen am M eercsgrund Stisswassere is ilberdecken . THE floating ice shelf which fills the southern end of McMurdo Sound may well be the strangest ice shelfin the world . To begin with , it has a dual origin in that the western portion is really the sea-level end of a short but steep high-level glacier named after Dr. Koettlitz, the doctor of Scott's Discovery expedition, while the eastern and greater portion of the ice shelf can be taken , at first sight, as a branch of the huge Ross Ice Shelf which has turned almost at right angles around the end of Minna Bluff to push its way between the three well-named islands, White Island, Black Island and Brown Island, mainly between the two latter (Fig. I). Almost every flight from the American McMurdo Sound air strip passes over part of the ice shelf, but it is still rarely traversed on foot because of the debris-strewn surface of its central part, shown in long lines of moraine, which are evidence for the movement of the ice shelf, probably at a very slow rate. The existence of this moraine shows in itself that there is annual loss from the surface, in direct contrast to the Ross Ice Shelf, where there is a yearly increase of up to a foot (30 cm. ) of compressed snow. It was therefore early suspected that to account for the extent of the moraine-bearing ice, there must be some increase from below to compensate for the loss from above. To appreciate the curious effect of this loss by thaw, one may reconstruct a traverse over the surface from the American air strip due west across the whole ice shelf to the western mountains . The air strip is on thick sea ice from one to three years of age and therefore 3 to S ft. ( I to I . S m. ) above sea-level. After three or four miles (S to 6 km. ) the sheet is nearer J S ft. (S m. ) thick, still mostly snow like immature or young shelf ice. Then rather suddenly the traveller begins to cross lines of surface moraine and the height above sea-level increases sti ll more until at the worst part of the crossing he may be So ft. (16 m. ) above sea-level. The surface is a lmost impossible for sledges, for not only is the covering of fine silt more and more dense, but one is crossing a myriad of thaw channels, which at the height of summer may be 3 or 4 ft. ( I m. ) deep. At the highest part he will cross one or two shear cracks showing that the ice coming from the Koettlitz Glacier is moving at a different rate from that of the eastern half. Once across the most silt-laden portion, the traveller is on a thinner shelf (perhaps IS ft. (s m. ) above sea-level), but still with fine silt in the ice which induces a tremendous flow of thaw water over the lower few miles of the g lacier. The duration of the thaw is extraordinary, beginning in November and rising to a peak in mid-January. But long after the air temperature has fa llen well below freezing point, the flow goes on under thin sheets of ice, right into March when visited by one of the Scott parties. With such extensive thaw in mind, it is no wonder that a recent drilling through the ice shelf

Foliation Pattern of Gulkana Glacier, Alaska Range, Alaska

Abstract: Gulkana Glacier, consisting of three major ice streams and two prominent ice falls, displays a complex foliation pattern. In the western ice stream, below Gabriel Ice Fall, the foliation is transverse, developing gradually down-glacier into a distinct series of nested arcs. The arcs are concave up-glacier with the foliation dipping steeply toward the inside of the arc. A similar pattern is displayed in the eastern ice stream but there the pattern is less distinct with the arcs evolving into a series of nested semi-arcs. The central ice stream is characterized by vertical layers of foliation with a longitudinal strike. Apparently, longitudinal foliation will form in areas with strong compression and shear caused by differential flow velocity such as where two ice streams unite. The foliation that ultimately displays arcuate (or semi-arcuate) patterns originates principally at the base of an ice fall where strong longitudinal compression is present due to the decrease of gradient.

The Bottom Topography of Gulkana Glacier, Alaska Range, Alaska*

Abstract: : As an extension of an intensive study of Gulkana Glacier a 42 station gravimeter survey was made to gain some insight into its third dimension. This survey showed that the glacier's main tongue occupies a complex valley composed essentially of two parallel channels separated by a medial ridge which extends southward from rock bastions in the accumulation zone. At midglacier the ice thickness in the larger eastern channel is 225 m., in contrast to 130 m. in the western channel. The medial ridge degenerates down-glacier probably disappearing within 2 km. of the glacier terminus. The basic surface flow pattern of the glacier described by Moores can be adequately explained by this basal topography. Seasonal velocity variations are possibly caused by melt-water basal lubrication with one channel being favored over the other at different times of the year, in agreement with observations by Elliston on the Gorner-Gletscher, Switzerland, and with the glacier sliding theory of Weertman. (Author)

Gravity measurements on the Devon Island ice cap and an adjoining glacier

Abstract: Gravity measurements ha ve been used to determine ice thicknesses across the western part of the Devon Island ice cap in the Canadian Arctic. A detailed profile of the ice-cap edge and a profile across an adjoining g lacier are a lso given. The ice cap has been found to have a la rgely rock core with ice thicknesses generally less than 500 m. A d eep valley has been found in the bedrock beneath the ice cap some 15 km. from the start of a draining glacier. The measured depths on the ice cap should be within 15 per cent a nd those on the g lacier within 20 per cent of the true values. REsUME. Mesures gravimitriques sur la caloue de glace de l'Ile D evon et d 'un glacier ejJluenl. Des mesures gravimetriqlleS ont ete lltilisees pour determiner I'epaisseur de la partie ouest de la calotte de glace de l'Ile D evon dans l'Arctique Canadien. On ajollte un profil detaille du bord de la calotte et un profil it travers un glaci er effluent. Les resultats montrent que la calotte de glace, reposant sur un la rge noyau rocheux, a un e epaisseur inferi eure it 500 m. On a trouve une profonde vallee dans le socle rochellx sous la calotte it 15 km environ d e I'origine d'un g lacier de drainage. La precision des m esures d'epaisseur est d e 15 % pour la calotte e t de 20 % pour le glacier. ZUSAMMENFASSUNG . SchwerkraftmessUllgen auf der Eishaube von Devon Island und auf einem benachbartell Gletseller. Zur Bestimmung von Eisdicken im westlichen Teil der Eishaube auf Devon Isla nd in der kanadischen Arktis wurden Schwerkraftmessungen herangezogen. Die Messungen erstreckten sich a uch auf ein Profil am R ande der Eishaube und auf ein Profil liber einen benachbarten G letscher. Es li ess si ch feststellen, dass die Eishaube grossenteils einen Felskern besitzt, liber dem die Eisdicke im a llgemeinen weniger a ls 500 m betrag t. lm Felsuntergrund d er Eishaube wurde 15 km hinter dem Anfang eines AbAussgletschers ein tiefes Tal entdeckt. Die gemessenen Eisdicken dlirften auf der Eishaube etwa 15 %, a uf dem Gletscher etwa 20 % genau se in .