geobotanical studies on the taku glacier anomaly

American Geographical Society

Geobotanical Studies on the Taku Glacier AnomalyAuthor(s): Calvin J. Heusser, Robert L. Schuster and Arthur K. GilkeySource: Geographical Review, Vol. 44, No. 2 (Apr., 1954), pp. 224-239Published by: American Geographical SocietyStable URL: http://www.jstor.org/stable/212357 .

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GEOBOTANICAL STUDIES ON THE TAKU GLACIER ANOMALY*

CALVIN J. HEUSSER, ROBERT L. SCHUSTER, AND ARTHUR K. GILKEYt

S TUDIES of ice recession in western North America have largely been made near the termini of glaciers; relatively few investigators have studied in the ice fields that nourish the valley drainage. But the ter-

minus presents only a partial picture of the fluctuations of a glacier, whereas observations of conditions and trends in its source region enable an insight into the entire pattern of change. A receding glacier may not be dwindling in its upper reaches, and a glacier may be sinking in the area of accumulation while the terminus continues to advance. Thus in order fully to understand the behavior of a glacier at its front, the changes taking place at higher elevations must be measured and evaluated. By means of such study a reasonable appraisal of future advance or retreat may be made.

On Taku Glacier, in Alaska, the main active drainage artery of the Juneau Ice Field (Fig. i), the geobotanical team of the I952 field party of the Juneau Ice Field Research Project undertook to determine the location, amount, and direction of the changes that had taken place since the general lowering of ice of the late-postglacial maximum. This glacier had been chosen for study for several reasons. The historical fluctuations of the terminus were known, the regimen of the glacier was being worked out by glaciologists of the project, and the anomalous advance presented a con- fusing issue in view of the world-wide recession generally in progress. This last reason was the most provocative, because the answer to the problem of Taku advance was to be found in the ice field proper.

These investigations upglacier may be considered a counterpart to those

* This is a report on one phase of the Juneau Ice Field Research Project, which is directed by the Society through contract with the Office of Naval Research. The cooperation and assistance of the following are gratefully acknowledged: members of the 1952 party, Departments of the Army and the Navy, the Tenth Air Rescue Group, and the U. S. Forest Service inJuneau. The first author wishes to

express his thanks to Yale University for the opportunity to pursue his part of this research under the Theresa Seessel Fellowship for postdoctoral study.

> DR. HEUSSER is geobotanist in the Society's Department of Exploration and Field Research and is in charge of the Juneau Ice Field Research Project. MR. SCHUSTER is on the staff of the Snow, Ice and Permafrost Research Establishment (Corps of Engineers) at Wilmette, Ill.; he has spent two seasons with the Juneau Ice Field Research Project. DR. GILKEY was leader of the Society's expedition to theJuneau Ice Field in I952. He was killed on Mt. Godwin Austen (K-2) in August, I953, while serving as geologist on the American Alpine Club Third Karakoram Expedition.



THE TAKU GLACIER 225

madeu (CE FIELD . importance

-58'3058

5 0 5 0 Km.

TAU YUKON TERRITORY

.....> .... .\8 ..CNAD

ISLAND ~ ~ ~ ~ ~ ~ ~~~~ ANA

Pacific Ocean

GEOGR. REVIEW APRIL 1954 13 13 4

FIG. ISketch map showing location of Taku Glacier. Arrows indicate main Taku drainage.

made by Lawrence' at the terminus. The work emphasizes the importance of the team approach in the solution of a problem, which is the underlying principle of the Juneau Ice Field Research Project. Investigators trained in different disciplines are working together in order to obtain a more compre- hensive knowledge of the problems relating to this ice field.'

TAKu GLACIER

The Juneau Ice Field occupies an area estimated at 700 square miles, largely on the southwestern slope of the Alaskan Coast Mountains and

I D. B. Lawrence: Glacier Fluctuation for Six Centuries in Southeastern Alaska and Its Relation

to Solar Activity, Geogr. Rev., Vol. 40, I950, PP. I9I-223; reference on pp. 208-2II. 2 W. 0. Field, Jr., and M. M. Miller: The Juneau Ice Field Research Project, Geogr. Rev., Vol.

40, I950, pp. I79-I90.



226 THE GEOGRAPHICAL REVIEW

north of the city of Juneau. At least I2 valley glaciers flow from this field, all of which reach low level in the Territory except two prominent streams that flow into British Columbia. Taku Glacier is the largest of those in Alaska and drains the largest area of the ice field. Its length of drainage, extending from the international boundary to tidewater at Taku Inlet, is about 32 miles; the firn region ranges approximately from 3000 to 6ooo feet in elevation. Several tributary glaciers empty into the Taku. Numerous nunataks occur along its upper drainage, and the last I2 miles are bordered by ridges projecting upglacier from the Taku Valley.

The evidence obtained by Lawrence3 suggests that at its maximum, in late-postglacial time, Taku Glacier completely crossed the valley, blocking the river and impounding a lake. When the glacier reached this maximum is not known, but in the middle of the eighteenth century it began to retreat from the valley. The age of the oldest trees on the ice-denuded surfaces is the basis for this date. A general retreat followed until the beginning of the twentieth century, when the Taku began a readvance that has since been more or less continuous. In more than 50 years the glacier has moved forward into Taku Inlet a distance of about three miles and a half

The time of the advance that caused Taku Glacier to obstruct the Taku Valley may be inferred from evidence gathered elsewhere on the periphery of the Juneau Ice Field. Mendenhall Glacier, flowing southwest from the same upper firn as the Taku, plowed into forest when it advanced in the late postglacial. Since the recent retreat of the glacier, stumps and other forest remains buried during the advance have been exhumed, and the wood has been dated by radiocarbon analysis as being I790 ? 285 years old.4 This radiocarbon date represents the approximate time at which ice that had begun to accrue at higher elevations with the onset of the "little ice age" reached the lower valley in which Mendenhall Glacier flowed forward. The "little ice age" followed the postglacial thermal maximum, dated, through radiocarbon content of wood buried in a nearby muskeg, at 3500 ? 250

years ago.5 On the basis of this information, the "little ice age" lasted in the outer valleys for some I300-I900 years. It can be inferred, therefore, that the advance of Taku Glacier to its maximum began about the beginning of the Christian era.

3 Loc. cit. 4J. L. Kulp and others: Lamont Natural Radiocarbon Measurements, I, Science, Vol. 114, 195I,

PP. 565-568; reference on p. 568. 5J. L. Kulp and others: Lamont Natural Radiocarbon Measurements, II, Scienice, Vol. iI6, 1952,

pp. 409-414; reference on p. 412. See also the following papers by C. J. Heusser: "Radiocarbon Dating of the Thermal Maximum in Southeastern Alaska," Ecology, Vol. 34, 1953, pp. 637-640, and "Pollen

Profiles from Southeastern Alaska," Ecological Monographs, Vol. 22, I952, pp. 331-352.




RESEARCH METHODS

The maximum advance of a glacier is known from the trimline which it produces during its outermost stand. A trimline results from the forward and lateral movements of the glacier as it plows into old forest. As the ice withdraws, moraines and outwash are formed, which are at first devoid of plants but are soon invaded by plants of the regional vegetation. Al- though in time the position of the trimline may be obscured by the later stages of succession, an analysis of the vegetation will show the former position of the ice. This is true only if not too much time has elapsed for the entire vegetation to become homogeneous. Fortunately, glacier retreat in North America is relatively recent, and even though in general more than two centuries have passed since the beginning of recession, trimlines are still outlined. Trees that seeded in on the earliest outwash when the glacier first began to withdraw contain in their growth layers a record of the approximate time since recession started. By means of tree-ring counts the beginning of the retreat can be dated, though not entirely accurately, since the length of time between the denuding of the terrain by deglaciation and the establishment of tree seedlings is usually unknown.6

These conventional methods are applicable only below timber line. Above the timber the trimline can be observed where the glacier cut the arctic-alpine heath. Often, however, this line is difficult to distinguish because of late winter snow, avalanching, and intercepting cirques. It is dis- continuous by comparison with the trimline in the timber; and because of the absence or paucity of woody plants containing annual growth layers, the age of the vegetation can only be estimated.

Botanical and geomorphic evidence was used to locate the former level of the ice on nunataks and ridges bordering Taku Glacier. The difference in elevation between this level and the present surface of the glacier was measured by means of an aneroid altimeter. The localities studied and measured are indicated by Roman numerals on the accompanying map, which was constructed largely from vertical aerial photographs (Fig. 2). The procedure at each locality was to "walk the trim" and note the available evidence above and below. The extent of the plant cover, its degree of development or successional stage, the soil thickness, and the number and kinds of plant

6 It is possible to determine this time if one has old photographs that give the date of ice with- drawal from a surface on which the age of the oldest trees is known. W. 0. Field, head of the Society's Department of Exploration and Field Research, and C. J. Heusser were able to determine this interval for glacier areas in the Canadian Rockies as between io and I7 years. Adding this to the age of the oldest trees at a locality for which the time of ice recession is unknown gives a more accurate date of the recession.




species were the major botanical or ecological criteria on which conclusions were founded. Geomorphic criteria included differential weathering, friction cracks, striations, polish, grooving, and topographic breaks in adjacent spurs. Travel was by skis, on foot, and by oversnow vehicle ("weasel"). Ground work was supplemented by aerial reconnaissance at different times during the field season.

BOTANICAL EVIDENCE

Several matters must be considered before the direct evidence from the field is taken up. Plant succession needs the greatest attention; the others are of secondary importance. By succession is meant the sequence of plants that ensues at a given site until a stage is reached that is not immediately altered further. At this "climax" the plant assemblage is said to be in equilibrium with the environment. Because of the various environments in the Juneau Ice Field, several different groups of plants will make up this stage. Environments vary largely according to available

FIG. 2-The Taku Glacier study area,

showing localities at which evidence

was gatbered and measurements taken.

?9 I 2 3 Mi. N )

frt~~~~~~~~~~~~4

1 1 /-~ >,~--~

'it1~~~~7

... ... ,/So .

C~~~~~~rsn ic '7 low \

-Y - --- dm

a tR b~~~~Lae,pslca leve or :exe,

/ I . / _, Contaoct:. RocA -ermanent snow or f/rn _ f aximnum area rrloge or nurnatak




moisture and soil; thus altitude, exposure, angle of slope, type of soil parent material, and degree of snow cover prescribe what plant group will develop at each locality. Each plant is governed in large measure by the interplay of these factors, and the ecological amplitude of the individual, in turn, de- termines its place in the region.7

The most conspicuous successions are on rock flour, on bare rock, along meltwater streams, and on talus (scree). Since it would take too long to describe each, the following succession is given as an example of that which occurs under mesic conditions on rock flour between timber line (about 3300 feet) and 5000 feet on the nunataks. The rush Luzula parviflora8 is usually the first invader, followed by the sedge Carex pyrenaica. These persist and subsequently come into association with the sedge Carex aenea, the rush Juncus drummondii, and the heath Cassiope mertensiana. Fireweed Epilobium latifolium and the saxifrages Saxifraga ferruginea and S. punctata ssp. pacifica may also associate if there is a moderate increase in available water. In time, as soil develops under increasingly stable conditions, certain plants are unable to persist as the environment is altered, and new ones replace them. When the last stage is reached, all but one of the above plants have been pushed out by invaders. Cassiope mertensiana remains and usually grows along with other heaths, Cassiope stelleriana, Phyllodoce glanduliflora, Loise- leuria procumbens, Vaccinium uliginosum, and Empetrum nigrum, and the club mosses Lycopodium alpinum and L. selago var. appressum. This assemblage in some places forms a thick cover of several hundred square meters on soils as much as half a meter in depth. Because of such disturbances as solifluction and avalanching, various stages of succession are found in this predominant group.

Generally, then, the plants above the trimline will be different from those below, will have attained a much higher stage because of a longer period without disturbance, and will exhibit a more nearly complete and more extensive ground cover. The area above the trim will possess a far greater number of species because of the existence of several different successional stages. Below the trim, only an early stage with a limited plant complement is usually found.

The kinds and cover of plants above and below the trim are sometimes not markedly distinct, and other factors determine this line. Mineral matter

7 The plant distribution is treated in C. J. Heusser: Nunatak Flora of the Juneau Ice Field, Alaska, Bull. Torrey Botan. Club, Vol. 8i, I954. (In press.)

8 Nomenclature follows Eric Hulten: Flora of Alaska and Yukon (in io parts), Lunds Univ. Arsskrft, N.S., Sect. 2, Vols. 37 (No. I)-46 (No. I), 1941-1950.




conditions the physical and chemical properties of the soil and may locally affect the microclimate. Plants, for example, are poorly distributed on diorite as compared with granodiorite. This may be attributable to a complex of causes. Weathered diorite produces large crystals of hornblende, which should have a lower water-holding capacity than the clay particles weathered from granodiorite. The dark color of diorite (low albedo) increases the amount of insolation; diorite soils are accordingly more rapidly deprived

0 igoo 20.00 FEET

B A

_____ ~~~19,52 glac/er surface GE0OGR REV.F'N, APRIL 19

FIG. 3-Sketch of trimline studied at locality XIII in Figure 2.

of water. Finally, because diorite lacks potash feldspar, derived soils possess little or no potassium, an important element in plant nutrition. It should also be mentioned that the presence or absence of such minerals as apatite (for phosphorus) and marble (for calcium) is likewise of importance in nutrition.

Avalanching causes the greatest amount of disturbance by introducing into the deglaciated area below the trim plants that would otherwise be absent there. Meltwater streams also introduce plants from the relatively undisturbed area above the trim: water-borne disseminules invade as well as those that are air-borne. Stream courses below the trimline usually possess a greater cover and diversity of plants than adjacent areas; this is probably a result of the higher water-holding capacity of the finer sediments in the stream course. After snow patches on the nunataks have completely melted and the streams have ceased flowing, this quality is an important factor. One last point should be mentioned, and that is the mycorhizae, or root fungi, which certain plants need to thrive. Heaths, particularly, depend on mycorhizae for survival. The absence of these would seriously alter the normal succession by preventing certain plants from becoming established.

Evidence from nunatak locality XIII (Fig. 2) is representative of most of the localities for which a change of level was determined. The general topography and location of the trimline are shown in Figure 3; the area



THE TAKU GLACIER 23I

indicated by the letter A will be discussed first. To the right of the col, 38 plants were listed above the triniline and 3 below: above, 24 vascular plants, i I lichens, and 3 mosses; below, 3 vascular plants only. The three plant entities below were sporadic on recently exposed rock flour; above, mats of sedge, grasses, and heaths were well developed on soils as much as a decimeter and a half in depth. Xeric and mesic habitats were apparent, with the plants characteristically associated with each at this elevation. The lists of plants on both sides of the trimline are as follows:9

ABOVE THE TRIMLINE

VASCULAR PLANTS

Lycopodium selago L. var. appressum Desv. Hierochloe alpina (Sw.) Roem. & Schult. Poa leptocoma Trin. Festuca brachyphylla Schult. Carex macrochaeta C. A. Mey. Luzula arcuata (Wahlenb.) Wahlenb. Luzula spicata (L.) DC. Luzula wahlenbergii Rupr. Salix sp. Silene acaulis L. Cardamine bellidifolia L. Saxifraga bronchialis L.

ssp.funstonii (Small) Hult. Saxifragafmrrrginea Graham Saxifraga rivularis L. Potentilla emarginata Pursh

ssp. nana (Willd.) Hult. Sibbaldia procumbens L. Empetrum nigrum L. Loiseleuria procumbetns (L.) Desv. Cassiope stelleriana (Pall.) DC. Vaccinium uligitiosum L. Primula cuneifolia Ledeb.

ssp. saxifragifolia (Lehm.) Hult. Campanula lasiocarpa Cham. Auttennaria pallida E. Nels. Artemicia arctica Less.

ABOVE THE TRIMLINE

MOSSES

Polytrichum piliferum Hedw. Calliergonella schreberi (Bry. Eur.) Grout Brachythecium salebrosum (Web. & Mohr)

Bry. Eur.

LICHENS

Alectoria pubescenis (L.) Howe Cetraria islandica (L.) Ach. Cetraria nivalis (L.) Ach. Cladoniia bellidflora (Ach.) Schaer. Cladonia coccifera (L.) Willd. Cladonia gracilis (L.) Willd. var. chordalis

(Flk.) Schaer. Cladonia mitis Sandst. Rhizocarponi disportirn (Naeg.) Mull. Arg. Soloritna crocea (L.) Ach. Stereocaulon paschale (L.) Hoffm. var.

alpinium (Laur.) Mudd. Thamnolia vermicularis (Swartz) Schaer.

BELOW THE TRIMLINE

VASCULAR PLANTS

Carex pyrenaica Wahlenb. Luzula wahlenbergii Rupr. Saxifragaferruginea Graham

Almost the same situation obtains in area B, to the right of the saddle (Fig. 3). Here 20 vascular plants were found above the trim and only 5 below. No lichens or mosses were listed. Thick heath mats were relatively widespread and were more highly developed than those in area A. Soils were as much as two decimeters thick above the trim; inorganic rock flour, a few centimeters deep, formed the substratum for the sparsely distributed plants below.

The level of the glacier on the nunatak showed evidence of falling in both areas. The upper deglaciated surface had the few plants mentioned; near the firn, plants were completely lacking. Other localities studied up-

9 Mosses were determined by Dr. Edwin T. Moul of Rutgers University, and lichens by Dr. John W. Thomson of the University of Wisconsin.




glacier showed a similar direction of change. Downglacier the level of the ice was found to be rising. Plants have formed an extensive cover below the trim, and the glacier was overwhelming them; at some places ice was push- ing over small trees, and here the trimline was more difficult to define. Above the trim the heath mat was well developed on a thick soil mantle, logs of old trees were found, and there were only a few scattered boulders. Below the trim the heath was only partly formed on thin soils, trees were fewer, there were no fallen logs, and boulders were strewn over the slope.

GEOMORPHIC EVIDENCE

The geomorphic evidence obtained by the field party leads in most cases to nearly thie same conclusions as the botanical evidence. Of the geomorphic criteria, differential weathering is the most useful for trimline interpretation. Above the trimline the present surface has been subjected to weathering since at least the postglacial thermal maximum. Below the trimline the more recently glaciated rock has been exposed to weathering only since about the middle of the eighteenth century. The younger surface is still fresh-looking and retains glacial polish, in contrast with the dull, weathered appearance of the rock above the trimline. The mafic minerals (ferromagnesian group) exposed in the granodiorite above the trimline have begun to deteriorate; below, these minerals show no sign of deterioration.

Additional evidence is presented by topographic breaks in the spurs that were transected by Taku Glacier during the late-postglacial readvance. As Taku eroded downward and outward, it steepened the faces of these spurs. Although the levels of the breaks may not be exactly coincident with the surface of the glacier during the late-postglacial maximum, they do indicate the maximum elevation of glacial abrasion.

The small-scale features of glacial action (striations, friction cracks, and grooves) are also of use in trimline interpretation. In many cases these showed that certain surfaces, recently glaciated yet above the level of the trimline, had been abraded not by Taku but by ice flowing into it from adjacent cirques. Thus in these particular cases such features were invaluable in determining the limit of trim. Apparently, cirques that are not active at present were debouching ice at the beginning of, and for some time following, the "little ice age."

Geomorphic evidence from locality XIII (Fig. 2) may be considered supplemental to the botanical evidence. A definite topographic break appears just to the right of the col (Fig. 3, A). This break coincides with a noticeable change in the amount of weathering. Tlle granodiorite in the col below the




topographic break is fresh, with no signs of deterioration of mafic minerals; glacial polish of the rock surface is common. Above, the surface of the granodiorite is dull, and mafic minerals are disintegrating. The saddle (Fig. 3, B) presents almost the same geomorphic evidence as the col. It is plain that both these narrow passes were glaciated during the late-postglacial maximum.

LATE-POSTGLACIAL MAXIMUM

When Taku Glacier reached its maximum in late-postglacial time, its average annual nourishment was far greater than at present. It was difficult, however, to ascertain at each locality investigated whether the trimline evidence available was a result of actual ice or of higher firn. In the area of accumulation the surface across the glacier between nunataks is generally concave. As the nunataks are reached, the accumulation becomes a progressively thinner veneer and finally wedges off. This thin cover presumably flows directly downslope and gradually joins the main glacier stream. Thus it was not necessarily the direct action of the glacier that produced the trimline on upper Taku; moreover, it is largely a result of the higher snow or firn on the margins of the nunataks. This level, developed to a maximum over the many years of the "little ice age," resulted in what has been called "trim" in this study. The trim at high level is accordingly produced in a different way from that on the lower glacier.

Downglacier, in the area of ablation, the transverse surface is convex. The edges of the glacier are much lower than points nearer midstream. Seasonal snow that collects along the margins has ablated by the end of summer. Raw ice is then generally exposed, and this produces the trirnline. There is little or no lateral fringe of snow-firn cover, characteristic in the accumulation area.

Since the firn line, separating the ablation and accumulation areas, was probably farther downglacier during the maximum, the trim over much of the parts studied appears to be largely the result of a higher permanent snow level on the bordering nunataks. The unevenness of the trimline (snow- formed) on the upper glacier and its sharp definition (ice-formed) down- valley attest to this conclusion.

Evaluation of the change in level was made with this information in mind. The amounts of lowering at the localities studied (Table I) are dia- gramed in Figure 4, with the data gathered by Lawrence in the terminal region.'" On the upper glacier, generally in the nourishment area, the level

IO Lawrence, loc. cit. [see footnote i, above].




I I:l JLIX1V VLIIvIVIIX x x[xiI XII XLV 5000 -

4000 | EAST PROFILES -I-'-T 1

3000- Late-postg/ac I surface

ZU 1952 surface 2000

1000

Sea level

I IL IIL1 zIV, V, 5000 -

4000 lo - WEST PROFILES

~30001 |La6e-pos6g/acia/ surface

LU 2 | /1952 surface u- 2000-

1000 3 6 Mi.

Seaa _ ___ z . . . S . GEOGR. REVIEW, APRIL 1%4

level

FIG. 4-Long profiles of the late-postglacial and 1952 ice surfaces of Taku Glacier from localities studied, showing amount and direction of change.

TABLE I-CHANGE OF LEVEL ON TAKU GLACIER

(Infret)

EAST PROFILE WEST PROFILE

PRESENT LATE-POSTGLACIAL PRESENT LATE-POSTGLACIAL

LOCALITY ELEVATION ELEVATION LOWERING LOCALITY ELEVATION ELEVATION LOWERING

XIV 4420 4980-5095 56o-675 V1 4715 5155 440 XIII 3940 4555 615 IV1 3905 4440 535 XII 3970 4520 550 XI 3585 4030 445 X 3385 3720 335

IX 2795 2895 100 VIII 2585 2700 115 III1 2750 2900 150 VII 2460 VI 2390 .... ... V 2135

IV 2010 2I3 5 125 III I860 2025 I65 II Terminus II Terminus .... I .... Terminus I Terminus



THE TAKU GLACIER 23 5

has fallen far more than along the lower reaches-as much as 675 feet, as compared with about I50 feet downglacier. Furthermore, the evidence indicates continued lowering above, whereas below, the glacier is encroach- ing on the recent maximum trimline.

These facts suggest a history of the fluctuations of Taku Glacier since the mid-eighteenth century, when the ice began to retreat after reaching its maximum. They also offer an explanation of the Taku advance at the beginning of the twentieth century while other glaciers originating in the ice field continued to retreat.

The close of the "little ice age" presumably brought about a lowering of Taku Glacier that progressively decreased with altitude. Ablation is most intense at lower elevations, and, consequently, it would be expected that lowering would be greater there than at higher elevations, as is true of neighboring Norris Glacier. Instead, the converse holds, and a mass of ice is advancing toward the trimline representing the maximum position attained when Taku Glacier reached across the inlet. Since this mass is presently advancing below the firn line (ablation overcomes accumulation here), the thickening of the ice cannot be attributed to net nourishment but, rather, must be a result of flow from higher regions. These data would therefore favor a wave interpretation to explain the anomaly of Taku advance. As the piedmont lobe of the glacier melted away and lowering continued, increased snowfall and/or less ablation occurred simultaneously at higher elevations. Subsequently, this resulted in a broad wave (or series of waves) of ice that moved downward and finally effected an advance of the terminus that has persisted through the last half century. The accumulation-ablation conditions at high elevations have since been such that they are unable to maintain a constant datum, and the level of the upper glacier has therefore been falling.ii

Terminal growth coupled with thickening has been reported for several Alaskan glaciers, such as the Carroll and the Hoonah in Glacier Bay.'2 Re- ceding glaciers may also show a surface rise. Nisqually Glacier on Mt. Rainier, for example, was measured several years along four cross profiles.'3 A

II This may not be true locally at the 6ooo-foot crest, where net accumulation seeins considerable. See C. J. Heusser: Palynology of the Taku Glacier Snow Cover, Alaska, and Its Significance in the Determination of Glacier Regimen, Amer. Journ. of Sci., Vol. 252, I954. (In press.)

12 [W. 0. Field:] The Variations of Alaskan Glaciers I93 5-I947, Proces-Verbaux, Unlion GCode'sique et Geophysique Internationale, Assemble'e Generale d'Oslo, 1948, pp. 277-282.

I3 Arthur Johnson: Nisqually Glacier, Washington: Progress Report, I95 I (U. S. Geol. Survey, I952; mimeographed). See also A. E. Harrison: Ice Advances during the Recession of the Nisqually Glacier, The Monttaineer, Vol. 43, No. I3, I95I. pp. 7-I2.




progressive rise of the ice surface downglacier is strikingly shown. Sometime in the recent past this glacier was nourished above to such an extent that ablation has not greatly modified the nourishment in its subsequent progress down-valley.'4

That the Taku has advanced while the other Juneau Ice Field glaciers have continued to retreat appears to be a result of its being nourished from a higher area. Its source region begins at 6ooo feet, whereas all the other ice streams except Llewellyn Glacier begin at 4000 to 5000 feet. Although Llewellyn Glacier, which shares the 6ooo-foot crest of the Coast Mountains with the Taku, is retreating, its retreat, along with that of the others, may be due to the fact that its ablation area is more extensive than Taku's and also to the fact that it probably receives less nourishment because of its position on the lee side of the range ("snow shadow" effect). It is thought that the broadness of Llewellyn Glacier, in contrast with Taku, which is confined in a narrow valley, would not favor great thickening, and thus any wave development would not be of sufficient magnitude to be detectable.

If the conclusions reached from these trimline investigations are correct, it can be suggested that Taku advance will continue until the ice wave presently moving in the downglacier defile dissipates at the terminus. It is not possible to prognosticate how soon this will be. Rates of movement and ablation are known from the lower ice, but these data are limited. The complexity of the area and of the controlling factors does not permit an exact prediction at this time. It seems probable, however, that the advance will continue for at least several years. The extent of lowering of the upper ice would seem to indicate that recession is eventually inevitable.

NOTES ON THE ADVANCE OF TAKU GLACIER

WILLIAM 0. FIELD

The advance of Taku Glacier since about I900 seems to be the greatest recorded for a valley glacier in the present century. Despite the accessibility of the area, this phenome- non has not been given detailed study, though the photographic record and various sur- veys provide a means of determining the approximate rate of advance and show the appearance of the terminus in different years. Two significant accounts have appeared:

14 It should be noted that the survey team of the I953 party on Taku Glacier ran several cross profiles

on the lower ice for comparison with those to be run in future years (personal communication from

Dr. Lawrence E. Nielsen, leader of the I953 expedition). For location (on the seismic transects pre-

viously made) see Figure 3 in T. C. Poulter, C. F. Allen, and S. W. Miller: Seismic Measurements on the

Taku Glacier (Stanford Research Institute, Stanford, Calif., 1949; mimeographed).




by Wentworth and Ray,'5 resulting from their observations in I93I; and by Lawrence,'6 describing his studies in I949.

Such an advance of a glacier is unusual today but was probably commonplace in the seventeenth and eighteenth centuries, somewhat less so in the nineteenth. At least six other large Alaskan glaciers are now more advanced than in I900, but, like the Taku, they are exceptions to the general trend, and their behavior is at variance with that of neighboring glaciers, flowing from adjacent neves.

The advance of the Taku terminus has been uneven, so that a measurement at any one point is not indicative of the average rate. A,more precise result is obtained by taking the average of three lines of measurement evenly spaced across the glacier. As was pre- viously stated,'7 the present advance is believed to have begun about I900. From I900 to I952, the advance measured at the middle of the terminus totaled about I8,200 feet, or an average of 3 50 feet a year. The yearly average advances in feet for the intervals between observations are approximately as follows:

I900-09 I909-29 I929-3I I93I-37 I937-4I I94I-48 I948-50 I950-52

3 85 272 6oo 522 525 27I I67 300

In the last interval the ice along the eastern part of the terminus welled out a total of some I200 feet, whereas the remainder of the terminus advanced only about 300 feet-an illustration of how misleading measurements may be if taken at only one point on an advancing terminus.

The terminus has advanced down the inlet in water that in I890 was 250 to 300 feet in depth.'8 By I937 a submerged push moraine that was building up in front of the advancing ice cliff had appeared above tide as a bar. Soundings by the United States Coast and Geodetic Survey'9 also showed an average depth of only a few feet along the base of most of the terminus. Subsequently the push moraine was gradually extended until in 1941 it was visible along most of the terminus. In the last few years, however, parts of the bar have at times either been overridden by the ice or been temporarily eroded away, so that sections of the terminus again became tidal in comparatively shallow water.

The advance of the terminus is now governed to some degree by three periglacial factors, two of which militate against further advance, while the other favors it. First, the glacier has now reached the end of the inner inlet and must necessarily expand as its terminus moves forward. Thus the headward pressure, or wave, of ice that is causing the advance tends to be dissipated over a larger area, and as the surface increases, ablation also increases. The second factor is the increasing resistance of the push moraine, which in the middle of the inlet attains a height from the valley floor of at least 240 feet and which now fronts the whole submerged part of the terminus. The third, and favoring, factor is

'5 C. K. Wentworth and L. L. Ray: Studies of Certain Alaskan Glaciers in I93 I, Bull. Geol. Soc. of America, Vol. 47, I936, pp. 879-933; reference on pp. 89I-893.

i6 Op. cit. [see footnote i, above]. 17 Ibid., p. 209.

A8 "Taku Inlet, S.E Alaska. By the party unter [sic] the charge of Lieut. Comdr. H. B. Mansfield ... 1:890." I: 40,000. U. S. Coast and Geodetic Survey hydrographic survey, photostatic reproduction.

'9 Shown on section of Hydrographic Survey No. H6267, surveyed in I937, on scale I: I0,000.

Photostatic reproduction.



23 8 THE GEOGRAPHICAL REVIEW

the increased protection of the terminus afforded by this push moraine from the strong melting effects of tidewater. The influence of this is well shown at glaciers where recession of a terminus resting in tidewater can be compared with that of an adjacent land terminus.

Observations of glacier advance are so meager that there is not too much informiation to draw on for clues to the future behavior of the Taku terminus. The most reliable indication would be the rising or sinking of the glacier surface some miles above the terminus. No indication of recent surface lowering for some miles above the terminus had been reported up to I953, but in that year marginal barren zones appeared, which would suggest the possibility that the maximum has been reached. In I953 additional reference points were established for future determination of change.

The I953 observations are recorded as follows:20

The Taku Glacier fluctuated somewhat during the I953 field season. When the glacier was first closely observed, it was not readily apparent whether the terminus had pushed beyond the I952 front as shown on United States Coast and Geodetic Survey chart H8032,21 or whether the surface of the glacier was higher or lower along the borders up the valley. Several changes were noted in the tidewater section of the terminus, notably two large embayments that had formed near the center of the front, from which small icebergs were being discharged. Later in the season when the fresh snow had disappeared from the ice, conspicuous barren zones were visible on both sides of the glacier as far up the valley as the south end of "Goat Ridge" [five miles above the terminus on the east side of the glacier], and the small push moraine along the front of the western part of the terminus (where the glacier ends on the alluvial flat extending from Norris Glacier) was separated from the ice ... 20 feet or more. . . . As the season advanced, the barren zones did not alter noticeably, but on a flight made September I0 the distance between the small push moraine mentioned before and the glacier had evidently become less, the glacier had readvanced I0 to I5 feet along nearly all the front bordering the moraine.

More noticeable, however, was a conspicuous bulge that had formed in the lobate central portion of the tidewater ice front. . . . This area appeared whiter and extended into salt water at high tide, forming a V extending from the otherwise uniformly curved front. This bulge had not been noted in the spring and appeared freshly broken and cre- vassed in late August when first seen. Evidently, a rapid advance was taking place at this small section of the terminus.

On July 9, and again 40 days later, the northeastern part of the tidewater front was visited. Here, for a distance of perhaps 500 feet, the glacier was advancing laterally against the forested cliffs. An advance of io feet had occurred during the 40-day interval, and the small stream bed between the glacier and the cliffs had noticeably narrowed. This advance appeared local; as one progressed up the margin of the glacier, one immediately entered the barren area, denoting a reduction of both the width and the depth of ice in the valley amounting to perhaps 20 to 50 feet. This distance between the ice and its former (I952?)

extent hardly changed at all during the 40 days. Some slight thinning had taken place at two points where checks had been made between 5 and I0 feet lower ice levels at the later date.

From these observations, it appears that Taku Glacier did advance slightly beyond the

I952 charted position, but that all this advance had taken place before the first observations

20 From a report, November 30, I953, by Austin Post, surveyor of the Juneau Ice Field Research

Project. 2I Hydrographic Survey No. H8032, preliminary compilation. Photostatic reproduction.



THE TAKU GLACIER 23 9

in I953, when a slight retreat was in progress. As the last check showed some slight readvance, and minor activity was noted at two local points, the glacier was at least in a state of near-perfect equilibrium during the summer, when ablation was at its greatest. Thinner ice in the valley immediately behind the terminus would not lead one to believe the glacier is likely to make any considerable advance beyond the I952 position; however, this thinning is not great enough to preclude this possibility.

It is strongly recommended that detailed observations of the terminus be made annually. The rise or subsidence of the ice surface in the lower part of the glacier should likewise be measured, and also observed by aerial reconnaissance. The glacier may be reaching its maximum extent in the present surge, or it may not. In any case, its behavior should be carefully noted, and a detailed record maintained during succeeding years to determine whether the next phase will b2 continued advance, relative equilibrium, or the beginning of recession. Such observations not only would contribute to a knowledge of glacier variation but would be of practical value for future economic planning in the Taku Valley.



geobotanical studies on the taku glacier anomaly

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