WHEN IT WAS COLD.

Timaru Herald, Volume XIIC, Issue 13892, 1 May 1909, Page 2

WHEN IT WAS COLD.

AY A K ATI Pl' UNDEJ? ICE. (By J. H.) The seventh ••Bulletin" issued by the geological survey under the new rule of Dr Hell, is a description of Lake Wakatipn and the country near it on the eastern side, and one chapter deals with the eHects of the glaciation of the district. Professor Park, the author in his introductory remarks says the point of greatest interest in the report is the presentation of proof that the Lake \Y akatipii region was once covered bv a continuous ice-sheet of vast depth—a continental ice-sheet that reached the sea, and probably covered the greater part of the South Island. The i><?sheet at the time of maximum refrigeration had a thickness exceeding 7000 ft. in the Wakatipu basin, forming a vast plateau, above which only the higher peaks appeared like strings of rocky islet® in a frozen sea. .

" feature of the land in the Lake Wak.'itipn region and from there southwards fo the plains of Southland and eastwards to tjie sea, tip to a height of GoOOft. above sea-level, are everywhere dominated bv evidences of ire-erosion on a wale of mncrnificoncc that is unknown elsewhere in the southern heir-isnhere.'and is perhaps without a parallel outside the polar reg-ons. The existing valley flaeiers of New Zealand rank among; the largest on the globe; hut they i»re as shrivelled 01Vmie? compared with' the maiestic sheet r»f movinc ire that in the Hacene period covered all but the highest peaks, uwl drove furrowing coulters deeply nto the sides of the resisting inotinains. . . . During the period of

greatest refrigeration the ice-shoot attained a maximum thickness probably exceeding 7400 ft." The evidences of .this great refrigera tion, described and pictured in the itul letin are convincing to any reader «lu knows anything about such evidences. "Along the floor of the valleys then are cskars, rock basins forming lakes and tarns,, roches moutonuees (whale backs), ice-grooved and striated hum mocks, true erratics, perched blocks, niorainic matter and till; on the foothills broad ice-cut platforms or benches: and on the slopes of the mountain ranges, tier upon tier of ice-cat benches and innumerable mammilated hummocks." ' m . The proofs of the existence of an icesheet are the marks of ice-abrasion high np the mountains and Professor Park found them —on the Remarkable? up to 6500 ft above sea-level, on the Kyre and Richards ranees lip to 6000 ft. Dome-shaped crests and terraced slopes tells us that even the liighpst penk® of lessor ranges north of the Remarkahlos were overridden by a continuous icesheet. The Professor points oi«t. thai ice must have a'considerable thickness in order to do any work leaving permanent marks on the rocks, and making what he deems a low estimate ot 750 ft to give the ice-sheet any abr«dii»« power, thus must be added to the <w>ooft above sea-level, the height of marks on the -Remarkables. But the bottom of Lake Wnkatiou is 240 ft below sea-level, so that the thickness of ice in the mid 1 die of the lake basin must have l>e«n 7490 ft., or nearly a mile and a liali! In the Arrow basin, he says, it must have been 5340 ft thick, which exceeds the 'computed maximum thick-ness-of the-ice-sheet covering Scotland in the glacial epoch of the northern hemisphere. Such a depth must give the ice great scooping power in the hollows where the maximum depths occur, as the weight of the mass of ice, in motion, however. slow, must crush the surface of any but the hardest rocks. As was mentioned above, fessor Park estimated a depth o£ 150 ft as sufficient to enable ice to abrade the Wakatipn rocks; what power then must 5000 and 7000 feet have had! The " Bulletin" contains many fine photographs of ice-rounded hummocks and ridges, moraines and eskars, being erratics, ice-ground and striated bosses and boulders, and one photograph of a truly remarkable set of ice-terraces —of which he counted thirty, one above another, seen on Ben More, looking ' across Lake - Luna, a small lake a few miles from Wakatipu. The history of the great ice-sheet, as now worked out, shows that it flowed in several directions from the great liollo\v of Wakatipu, east and west as well as along the main line southwards; but the streams did- not appear as valley glaciers like the Tasnian of the present day, they were merely the more forcibly moving deeper portions of an icesheet spread over the whole country, save a few of the higher mountain tops, and the Professor concludes that all the hill country of Otago and Canterbury was in the sanife condition. THE GLACIER THEORY.

The question of the ability of a glacier to excavate a rock bed is inquired into .in this "Bulletin," and Professor Parte has thrown a new light upon it, by pointing out that given sufficient weignt of ice moving over arock, the surface must be crushed, as is the surface of a road under a heavy load, and the crushed material would then be easily removed. As mentioned above; he made an estimate of the minimum depth ot ice required to crush and abrade the rocks of the Remarkablcs at 750 ft. Another scientific question dealt with is the nature ot ice-flow, and Professor Park too easily accepts Forbes' theory. He states that the movement of a glacier "is now conceded to resemble in nearly all respects the flow of a river." He does not explain that reservation "nearly," and under that reservation is hidden an all-important difference between a glacier and a river. The author says—and adds a couple of diagrams to further explain what he says—that a glacier flows faster in the .middle than at the sides, and faster at the surface than in its depths. In a paper published in the "Transactions" of theNew Zealand Institute of 1890, 1 proposed a theory of ice-flow which denies that'the surface ''flows" at all. The view expressed in that paper is, in brief, that ice flows when under suf-ficient-pressure (just as Carrara marble can be made to flow, as mentioned by Professor Park in his paper); that in a glacier or ice-sheet of sufficient thickness, the upper portion supplies that pressure upon the portion beneath it, causes this to flow, and in flowing it bears the upper portion along as a floating load. One cannot see this, optically, but it is easily visible to the eye of the imagination—by that faculty to which Tyndall taught us to apply the German term " vorstellungcraft." If the surface of a glacier flowed, the phenomena of flowing should J>e most clearly apparent where the glacier moves fastest down the stei>i>er grades of its course. It is, however, just ou these steeper grades that the surface becomes crevassed, discontinuous, loses all sign of flow except movement. Look at a typical ice-fall, or a photograph of one—the Hoehstetter lor instance—and one sees no suggestion of surface flow. What one does see is explained by a theory of pressure flow, and floating load supplying the pressure. There are allusions in Professor Park's discussion of the subject to "gravitational stress" which appear to belong to this ♦ li«orv, and not to Forbes' theory at all.

Apropos of tli** glacier theory (liiis lias nothing to do with the "Bulletin," but with the glacier theory at large), it is strange that no one seems~ito have enquired what becomes of the air which is inmrisonecl in neve ice, and what part it plays iu the history of th« plncier. Jt must produce one set of effects oil being compressed by deep

burial in the novo and glacier, and another sot of effects when expanding on being partially relieved from pressure as the glacier thins out. Compression warms it. which involves the melting of some ice about it: expansion cools it, which" invbWes the freezing of some of the water with which the glacier ice is saturated. The-precise effects of these changes of temperature in the imprisoned air must be worth studying. Perhaps they have something to do with the production of that peculiar "structure" of' the ice to which Forbes attached sn imnh importance.