BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA

VOL. 44, t=P. 575-600, II FIGS. JUNE 30, 1933

PALISADE OF THE HIGn SIERRA OF CALIFORNIA1

BY 0. D. TON ENGELN (Presented before the Geological Society, December 27, 1929)

CONTENTS Page Introduction...... 575 Palisade Glacier...... 576 Location ...... 576 Size, altitude, former extension...... 579 Movement and crevasses...... 581 Moraines and glacier tables...... 583 Glacial chutes...... 585 Glacial pavement...... 589 Glacier stairway and pater noster lakes...... 590 Introduction...... 590 The cirque...... 592 Retreat of the cross-wall...... 594 Origin of the cross-wall...... 595 Basins and steps below the cross-wall...... 597 >% __

I ntroduction Between , latitude 35° 40' north, altitude 5248 feet, and Tioga Pass, latitude 37° 35' north, altitude 9941 feet, a distance of 158 miles on a north and south lirLe, there are no highways across the high, eastern front of the Mountains of . This great barrier to travel on east and west lines is commonly referred to as the High Sierra. The greatest elevation on its crest line is , 14,496 feet, the highest summit in the United States. From Mount Whit­ ney, at latitude 36° 35' north, the elevation of the. crest line declines southward rather regularly in 65 miles, on a north and south line, to the elevation of Walker Pass. North of Mount Whitney there is, however, only little change in elevation of the h;gher points in the 93 miles to Tioga Pass. Thus, , latitude 37° 6' north, has an elevation of 14,254 feet, and , latitude 37° 44' north, 13,090 feet. These peaks,

1 Manuscript received by the Secretary of the Society, January 26, 1932.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 576 O. D. VON ENGELN---PALISADE GLACIER

and the many others along the crest line, are held to be monadnocks rising above an old erosion surface, the Subsummit Plateau, that constitutes the upland level of the western slope of the Sierra Nevada. As the aver­ age altitude between peaks of the Subsummit Plateau is 11,500 feet, the scarp of the High Sierra from Mount Whitney northward presents an imposing wall (figure 1) towering 8000 feet above the floor of the Owens Yalley at its base. In this section, below Mount Sill, is Palisade Glacier, the southernmost glacier in the United States (figure 2).

F ig u r e 1 .—Section of the Crest Line and dissected Scarp of the High Sierra half way between Split Mountain and Mount Sill Telephoto view across the summit of the Inyo Range. Viewpoint is 30 miles distant from the Sierra summits. Photo by Carl Allen.

P a l is a d e G l a c ie r

LOCATION

There are several references in geographic and geologic literature to the effect that the southernmost glacier of the High Sierra “is a few miles north of Mount Whitney” 2 and “the small glacier in latitude 36° 35' near Mount Whitney now seems to be the (glacier in the United States)

2 N. M. Fenneman : Thysiography of Western United States. New York, 1931, p. 41C».

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 io PALISADE GLACIER F e r u g i .— 2 kth a o te ein f h Plsd Gair California Glacier, Palisade the of Region the of Map Sketch \ i e lic .\A + ,11 III 0 vC VU*.* M' W' vux ^ n -'

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 578 0 . D. VOW ENGBLJST----PALISADE GLACIER

farthest south.” 3 The glacier is reported to exist at the head of a cirque of East Pork. The cirques of East Pork are west of the crest line of the Sierra Nevada scarp but open directly to the north, hence are under the shadow of Mount Russell and Mount Young. Further, they are pro­ tected from the east and the west sun by high and steep ridges extending north; these ridges are the sides of the cirque amphitheatre. The site, accordingly, is extremely favorable for preservation of a glacier. How­ ever, the area available there that is above the level of 12,500 feet would only suffice for a minute cliff gacier. The glacier is supposed to be under the shadow of Russell which is only 14,190 feet high. Hence, the presence of a glacier in those parts can not be ascribed to the superior height of Mount Whitney. If this one does not exist, no glacier is present west of the scarp line for the distance of a degree of latitude farther north, and there the small Darwin Glacier, the terminus of which is at an alti­ tude of 12,500 feet, occupies the head of a cirque that also faces directly north. Lawson 4 evidently saw the cirque at the head of the south branch of East Fork but makes no mention of an existing glacier. He makes note, however, (op. cit., p. 366) that according to J. N. Le Conte “ still linger in the cirques of the summit divide but a short distance north of the head of the Kern.” The Mount Whitney, California, quadrangle topographic sheet of the United States Geological Survey, 1919 edition, shows neither a glacier nor even a snowbank at sites around latitude 36° 35' north. John M uir5 asserts he “made excursions over all the High Sierra” in search of glaciers (page 24) and that he found 65 existing residual glaciers “in that portion of the range lying between latitude 36° 30' and 39°” (page 20); but Mount Whitney . . . does not now cherish a single glacier. Small patches of lasting snow and ice occur on its north­ ern slopes, but they are shallow, and present no well marked evidence of glacial motion (page 35). If Muir had said that the existing glaciers of the High Sierra are found north of 37° instead of 36° 30' he would have been precisely accurate. At 37° 4', in the upper levels of the large cirque at the head of the South Fork of Big Pine Creek, there are mapped seven distinct glacierets, the largest of which is about half a mile in each

3 A. Knopf: A geologic reconnaissance of the Inyo Range and the eastern slope of the southern Sierra Nevada, California. U. S. Geol. Survey, Prof. Pap. 110, 1918, p. 105. (Knopf’s source for the statement above is a paper by R. E. Dickerson : Whitney Creek, its glaciation and present form, California Phys. Geogr. Club Bull., vol. 2, 1908, pp. 14 to 21.) 4 A. C. Lawson: Geomorphogeny of the upper Kern Basin. Univ. California Publica­ tions, Bull. Dept. Geol., vol. 3, 1903, p. 353. s : Mountains of California. New York, 1894, 1911, p. 34.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 PALISADE GLACIER 579

dimension. These ice masses were seen only from a distance by the author. They are small and possibly do not exhibit the characteristic of a true glacier—motion within the mass. The cirque basin at the head of the South Fork of Big Pine Creek in which these snow patches persist opens to the nortJ¥*and northeast. The mountain wall, “,” elevation 14,049 feet, under which five of the glacierets occur, has a west to east trend. It is this northern exposure with consequent “broad frosty shadows” (Muir) that determines this most southerly site of lingering glaciation. The same conditions, accentuated, three miles farther north at the head of the north branch of Big Pine Creek (figure 2) and under the shadow of three peaks approaching Mount Whitney in elevation (Mount Sill, 14,254 feet; Mount Winchell, 13,749 feet; and Agassiz Needle, 13,882 feet) have fixed the site of Palisade Glacier, the most southerly glacier in the United States, and have enabled it to maintain itself in dimensions greater than those of rival glaciers situated farther north.

SIZE, ALTITUDE, FORMER EXTENSION Palisade Glacier, as mapped by the United States Geological Survey in 1909, is more than one and one-half miles long in its greater dimen­ sion—that is, parallel to the “palisade” mountain wall at its head. From the mountain wall forward to the moraine at the widest part is nearly three-quarters of a mile. The Mount Lyell Glacier, on the northern slope of Mount Lyell, latitude 37° 45' north, is stated by Russell6 to be the most extensive existing glacier in the High Sierra and to be “less than a mile in length with a somewhat greater breadth.” The Mount Lyell Glacier is thus approximately 50 miles farther north than the Palisade Glacier, but much smaller. No less than 15 small fields of ice that might appropriately be termed glaciers or glacierets are present in the section of the High Sierra between the Palisade Glacier and the Mount Lyell Glacier. However, every one of these is much smaller than either the Palisade Glacier or the Mount Lyell Glacier. Like the two larger glaciers, the smaller glaciers exist, almost without exception, in cirque depressions at sites where a high mountain wall has a distinctly east-west trend, giving a northern exposure to a basin on the southern wall of which the glacier clings. The altitude of the head of Palisade Glacier is 13,000 feet; of its front, approximately 12,500 feet. The Mount Lyell Glacier is between

« I. C. Russell : Glaciers of North America. Boston, 1901, p. 38 ; Existing glaciers of the United States. U. S. Geol. Survey, 5th Ann. Eept. 1883-84, p. 315.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 580 O. D. VON ENGELN---PALISADE GLACIER

F ig u r e 3 .— Overflow Tongue from upper Level to lower Level of Palisade Glacier Note transverse crevasses, medial moraine, and “chutes.”

F i g u r e 4 .— General View of the Site of the Palisade Glacier Shows the two divisions of the glacier, moraine at the front of the upper level division, the cross wall at the head of the valley trough, “ice tongues” or “chutes,” and the highest of the lakes. Photo copyright, H. W. Mendenhall, Big Pine, Cali­ fornia.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 PALISADE GLACIER 581

12,500 and 12,000 feet in elevation. Evidently the 500 feet greater eleva­ tion at the more southerly site compensates for the difference in latitude. It is interesting to note that Knopf (op. cit., page 96) says that the Pleistocene glaciers of Big Pine Creek descended to an altitude of 5000 feet, “the lowest descent so far discovered on the east flank of the Sierra Nevada.” The Pleistocene glaciers that, farther north, descended to the plain of the basin ended at elevations above 6000 feet.

F ig u r e 5 .— Lower level Palisade Glacier Note bergschrund cutting across “ice tongues” or “chutes” in cirque head-wall. Con­ nects on left side with figure 3.

MOVEMENT AND CREVASSES The Palisade Glacier has two, well-defined parts, of which the south­ ern and eastern division is by far the larger and has the higher altitude. In consequence of its greater elevation the larger division overflows laterally northeastward to join the lower level part (figure 3). This overflow partially fills a notch in a spur from Mount Winchell which projects as a buttress between the two ice sheets. The overflow is not clearly shown on the topographic sheet (Mount Goddard quadrangle). This map presents the two divisions of the glacier as continuous at their lower end. From this fact it may be inferred either that the glacier has

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 582 0. D. VON ENGELN ---- PALISADE GLACIER

shrunk very considerably since 1909 when the survey for the map was made or that a snow cover masked the lower projection of the Mount Winchell spur at the time the mapping was being done. The alternative explanation is unlikely, however, because the view shown in Figure 4 was evidently made early in the spring when large snow patches were still present in the hollows of the lower slopes, and it shows this projection prominently exposed.7 I t can be noted in Figure 3 that the slope of the surface of the overflow tongue is distinctly steeper than the surface of the upper level glacier and than that of the lower division. In fact, the overflow is an ice cascade, and as such displays well developed transverse crevasses at and below the crest line. The phenomenon of this overflow and its transverse crevasses demon­ strates conclusively the true glacial nature of the Palisade G-lacier. Pali­ sade Glacier is not merely an inert mass of ice lingering in a corner of an ancient cirque. Instead, the upper section has sufficient volume and active motion to spill laterally across a low divide between its two parts. That the masses of both divisions of the glacier are in motion is imme­ diately evident from the perfection of development of the bergschrund. In Figure 4 it can be seen that the line of the bergschrund follows along the line of the mountain front quite continuously, though the picture was taken in early spring when the cover of snow on the glacier was still deep. The perfectly developed bergschrund is shown in the picture of the lower, or Glacier, taken October 7, 1929 (figure 5). Other crevasses, transverse, appear below the bergschrund in the upper level, or South Palisade Glacier, and the section these expose (figure 6) shows clear ice with no evidence of layers of snow. Like Figure 5, Figure 6 was taken October 7, 1929, about the beginning of the winter season. There was a light fall of snow in the morning, and the temperature was below freezing at the altitude of the glacier surfaces, so that the ice was dry and hard.

7 Harlow M. Stafford, Snow Supervisor, Department of Public Works, Sacramento, California, courteously furnished the author with a transcript of the State’s Snow Survey of snow depths at 10,000 feet above tide on Big Pine Creek. The record extends from 1926 through 1931. The period is too short to permit any correlation between snow­ fall and change in the Palisade Glacier. However, the great variation during these years (1926, 31 inches; 1927, 88 inches; 1928, 36.9 inches; 1929, 37.6 inches; 1930, 38.1 inches; 1931, 16.8 inches; all measurements made at approximately the same date, near the end of March or the first of April) indicates that if there should be a succession of years with exceptionally low or exceptionally high precipitation there could be marked fluctuation in the size of the Palisade Glacier. Stations with records that extend through a longer period (maximum 25 years) are too distant and in situations too unlike those in the Palisade Glacier area to be significant.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 PALISADE GLACIER 583

MORAINES AND GLACIER TABLES As W. D. Johnson made clear,8 blocks of rock are detached from the cirque wall at the bottom of the bergschrund and are incorporated in t he forward-moving ice of the glacier. This process is much facilitated in the region of the Palisade Glacier by the well-developed block jointing of the granite of the cirque wall. This wall, moreover, appears to have

F ig u r e 6 .— Crevasse in upper level Palisade Glacier Photo by T. Rust.

been maintained much steeper in the Palisade Glacier section (by the sapping recession of the bergschrund) than at the Mount Lyell site, where Johnson made his observations. As a consequence, weathering, though active, has not kept pace with the recession due to the bergschrund, and the “palisade” cliff of the cirque head is very steep. Hence, great joint

8 W. D. Johnson : M aturity in Alpine glacial erosion. Jour. Geol., vol. 12, 1904, p. 574.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 584 O. D. VON EN G ELN ---- PALISADE GLACIER

blocks of the granite, loosened by frost action or undermined by the bergs- chrund recession, are precipitated directly upon the glacier surfaces in considerable numbers. I t appears also (figure 3) that some rocky debris is incorporated in the moving ice by erosion of roches moutonnées. Ac­ cordingly, there is an abundant supply of rock fragments for transport as englacial and surface moraine. The development of glacier tables is promoted by the presence of many large blocks of rock that plunge down from the cliffs and come to rest on the surface of the ice (figure 7). Although to be positive, one would need to witness a fall, still it is not improbable that blocks of rock, which plunge from the higher levels of the cliffs, roll and slide completely across the glacier and come to rest in the end moraine at its front. Goldthwait9 has suggested such an origin for the “great heap of blocks on the floor of King’s Ravine.” He says when “the ice border retired it left only stagnant masses of ice at the heads of these cirques, which served as toboggan slides for loose blocks that fell off the oversteepened headwalls as soon as the ice support was withdrawn.” However, as indicated above, the ice over which the slid­ ing takes place may be an active cirque glacier. This possibility was early recognized by Richter,10 who said that the material of the cirque wall “loosened by weathering is removed by the glacier or slides off over the névé to form either actual moraines, or, at least, névé moraines.” The end moraine of the upper level, South Palisade Glacier, has a front of the steepness of the angle of rest of the material composing it (figure 4). This development is in accord with the idea of dumping and sliding from the upper surface. As the material is coarse and angular, the slope is steep, giving the effect of a wall. Probably the moraine here is a veneer supported at the rear by the ice of the glacier, which has a front equally steep and high. A rapid shrinking of the ice would result in a slumping of the rocky débris to the inverted Y cross-section characteristic of deposited morainic ridges. The end moraine of the lower level, North Palisade Glacier (figure 5), appears to be derived in greater volume from the melting out of débris carried englacially. It rises slightly above the end of the glacier (Octo­ ber, 1929), apparently because it serves to protect ice under it from melt­ ing as rapidly as the ice up-glacier, which is free of débris. The fact

9 J. W. Goldthwait : Geology of New Hampshire. New Hampshire Acad. Sci., Hand­ book No. 1, 1925, p. 12. i° E. Richter : Geomorphologische Beobachtungen aus Norwegen, Sitzungsber. Wiener Akad. Math. Naturw. KI., vol., 105, 3896, Abt. 1, pp. 152-164; quoted by W. H. Hobbs: Characteristics of existing glaciers. New York, 1911, 1922, p. 14.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 PALISADE GLACIER 585

that a patch of what may be termed medial moraine appears (figure 5) in line with the buttress of Mount Winchell gives support to the deduc­ tion that much of the material of the end moraine of the lower glacier is englacially transported. A pronounced medial moraine, which gives a distinctly convex surface to the overflow tongue from the upper to the lower glacier, is evidently derived (figure 3) from a longitudinal spur

F ig u r e 7 .— Glacier Table on upper level Palisade Glacier View looks down valley of the north fork of Big Pine Creek. Photo by Robert Sheridan.

of rock that projects at the brink of the descent. The undue amount of lateral moraine that appears on the left side of the overflow tongue (fig­ ure 3) may be explained as the result of the conveying around the corner of part of the end moraine of the upper-level glacier.

GLACIAL “CHUTES” In 1884, Russell11 called attention to a feature of the Sierra Nevada glaciers which he called ice-tongues. He says :

111. C. Russell : Existing glaciers of the United States. U. S. Geol. Survey, 5th Ann. Kept., 1883-84. pp. 3i6. 323.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 586 0. D. YON ENGELN---PALISADE GLACIER

F ig u r e 8 .— Glacial Chute on Cross Wall below the Cirque Basin of Palisade Glacier Note the close jointing of the granite.

F ig u r e 9 .— Roche Moutonnée in Glacial Chute, down valley from Site of Figure # Note up-hill direction of striations on stoss side.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 PALISADE GLACIER 587

“In the steep amphitheatre walls overlooking the névés of the glaciers there are frequently deep narrow cliffs [sic; a misprint for clefts] leading toward the higher peaks. In many instances these are partially filled with ice which shoots up above the névés in tapering tongues some hundreds of feet in height. . . . These ‘ice-tongues’ are an interesting feature of the Sierra glaciers . . . ; whether they have motion or not remains to be determined.” In a later publication12 he writes further about these ice tongues and says that the base of the largest of these in the glacier is cut off by the bergschrund—a suggestion that motion of the ice tongue, if any, is slower than that of the main glacier. He refers to John Muir’s description (1872) of narrow high-grade canyons, called “devil’s slides,” “devil’s lanes,” etc., which occur about the higher peaks and are fre­ quently occupied by ice. These ice-filled gorges were evidently present where there was no development of a cirque glacier. In one of these gorges the ice was found to have a motion of a fraction of an inch a day. Russell adds that such masses of ice are what he calls “ice-tongues.” If they do have movement, as Muir asserts, they may be regarded as the last, faint expression of active glaciation in mountain regions that have been deeply cirque-incised. Similar ice tongues are conspicuous features in the head walls of both parts of the Palisade Glacier (figures 3, 4, 5). In early spring and in late fall all these ice tongues appear to be cut across by the bergschrund where they join the mass of the cirque glacier. Hence, the motion, if they do flow, must' be slower than that of the cirque glaciers. Observa­ tions to determine whether the bergschrund during the summer gapes less widely and less deeply opposite these ice tongues than along the wider spurs might afford evidence on the question of motion or relative movement. The jointed structure of the Sierra granite in the region of the Palisade Glacier unquestionably is the factor that greatly promotes the develop­ ment of the gorges that hold the ice tongues. As these gorges remain filled with ice and snow to the end of the melting season, their sides and bottoms are not exposed to weathering processes. Accordingly, the fact that they are maintained as recesses in the walls at the head of the cir­ ques—walls that are receding through the bergschrund sapping—-in itself indicates quarrying action, or plucking, by ice motion. Given movement, that process, in view of the steep gradient of the ice tongues and the blocky structure of the granite with the vertical joints most prominent and well developed, should be very effective.

“ I. C. Russell: Glaciers of North America. Boston, 1901, pp. 39, 47, 50.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 588 0. D. VON" ENGELN ----PALISADE GLACIER

Similar channels, below the ends of the cirque glacier, now free of ice were referred to as “chutes” in an abstract13 published by the author. Since then a paper14 has appeared describing a remarkable series of analagous channels on the steep slope of Mount Puy Puy, Peru. I t is interesting to note that Harvey fixes on “glacial chutes” as the most appropriate term to designate such channels, and suggests its adoption for technical usage. The rock slopes below the Palisade Glacier are glacially rounded to a marked degree across the whole width of the cirque basin, and are prac­ tically free of weathering waste for a distance of a mile forward and 2000 feet down from the front of the glacier, as is well shown in Figure 4. Such rounding and absence of waste indicate that this area was freed of ice in comparatively recent time. But.it will be noted in Figure 4 that just below the fronts of the existing glaciers there are wide gaps between the knobs of rock rounded by glacial scour. Further, these broader gaps are cut into by narrower, straight-sided trenches that, in Figure 4, are filled with snow. However, in Figures 8 and 9, which are detail views made in early autumn—the first, close to the glacier front; the second, half a mile or more down the valley—it will be noted that these trenches have considerable depth. Knopf15 refers to a lesser development of the same phenomenon as follows: “long narrow trenches, bounded by vertical joint faces and as much as 6 feet deep [are] clearly indicative of ice plucking, having been excavated on the summits of roche moutonnee ridges.” The upper ends of such channels are the direct and lowest out­ lets from the cirque basins and would convey the first overflow of ice, if there should be an increase in the volume of the existing glaciers, across the steep slope below the cirque basin. That they have served as channels for ice movement is clearly demonstrated by the ice-smoothed surface at the left in Figure 8 and by the perfect roches moutonnees in Figure 9. Again, the marked jointing of the right wall of the channel in Figure 8 indicates the significance of such structure in the excavation of these trenches. In his description and interpretation of the Mount Puy Puy chutes, Harvey emphasizes precisely the same phenomena. The Mount Puy Puy troughs plunge down the face of a steep escarpment at the base of the mountain; glaciers are present today a few hundred feet above the

13 O. D. von Engeln : Palisade Glacier, Sierra Nevada Mountains, California. Bull. Geol. Soc. Am., vol. 41. 1930, pp. 99-100. w R. D. Harvey : Glacial chutes from the Peruvian Cordillera. Am. Jour. Sci., 5th ser., vol. 21, 1931, pp. 220-231. 15 Op. cit., pp. 101-102.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 PALISADE GLACIER 589

heads of the chutes ; the slight amount of weathering and stream erosion indicates that ice occupied the troughs not many hundreds of years ago; the bottoms of the troughs show glacial polish and rounding ; the rough form of the sides is'governed by joint blocks; and parallel and intersecting joint fissures determine the straightness of the channels. It appears, accordingly, that Muir’s “devil’s slides,” Russell’s “ice tongues,” the “chutes” of the Sierra referred to by the present writer in the abstract quoted above, and the Mount Puy Puy “chutes” are homol­ ogous phenomena. Further, these glacial chutes are significant for studies of glaciation in that they exemplify the extreme expression of a characteristic of glacial action—namely, differential erosion. In the development of such chutes it is demonstrated that a large movement of ice directed by major topographic elements tends to be concentrated in particular channels by variations in the structure of the rocks, and once it is so localized, differential erosion and its effects are progressively enhanced. In the parts of the chutes close to the existing glacier fronts the sur­ faces are, in general, rough from vigorous plucking action. Farther down, rounding, smoothing, and striation are more and more in evi­ dence, and, in turn, these features gradually disappear as the effects of weathering become more pronounced down-valley. That the movement of the ice follows the contour of the chutes very closely is remarkably demonstrated by the inclination of the glacial striae. Where there is a steep descent the striae slope with it across the rock surfaces of the side walls. Where there is an obstruction to flow, the striae go up hill. This effect is so well developed that it shows perfectly on the roches mouton­ nées, large and small, in Figure 9. In this view the widening of the chutes and the effects of weathering down-valley are also clearly illustrated. GLACIAL PAVEMENT An interesting feature of the bottoms of the chutes close to the glacier front is a peculiar kind of rock pavement made up of small, angular rock fragments. Despite the angularity of the constituent particles the sur­ faces of such pavements were essentially smooth. Such deposits would appear to be ground moraine, pressed in place by the ice, from which the finer material had later been washed by the trickling flow that com­ monly results from the melting of banks of snow. Meanwhile, the larger rock fragments keep settling down and fitting in to make a near mosaic. Gilbert16 stated that a somewhat similar development between two till

16 G. K. Gilbert : Bowlder-pavement at Wilson, New York. Jour. Geol. yol 6 1898 pp 771-775.

XXXIX—B u l l . G e o l . S oc. A m ., V o l . 44, 1933

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 590 0. D. YOK ENGELN ----PALISADE GLACIER

sheets of the Pleistocene glaciation was due to the partial erosion of the subjacent till by a re-advance of the ice. As bedrock is immediately be­ low the pavement of the Sierra chutes, this explanation could not apply there. On the other hand, a gentle sheet flow of water from a wide glacial front might carry away fine material in such amount that a re-advance of the ice would press the exposed boulders into a pavement in the man­ ner described by Gilbert. Tarr17 calls attention to the fact that over deposits of glacial-lake clay, there is, in places, a sufficiently continuous veneer of stones to give the surface the appearance of a till sheet, although pure clay, three feet or more thick, lies beneath. He says he has no satis­ factory explanation for the phenomenon. If pressed down by a re-ad­ vance of the. ice such a veneer would also provide a boulder-pavement effect. G l a c ie r S t a ir w a y a n d P a t e r N o s t e r L a k e s INTRODUCTION Each author referred to above as an observer of glacial phenomena in the High Sierra is impressed by the notable development in this region of the feature variously designated as a giant stairway, cascade stairway, cyclopean stairway, glacier stairway, or pater noster lakes. Some of these writers mention factors that they consider to be significant for the exist­ ence and marked development of the phenomenon. It is stated, in gen­ eral, that the stepped tarns are eroded from the solid rock, and that a strong local control of glacial sculpture is exercised by jointing. The accounts that are devoted to a systematic exposition 18 of the phenomenon simi­ larly find differences in rock structure to be a factor in the excavation of the basins, but emphasize also the nature of the glacial erosive processes, the effect of differences in the measure of the valley cross-sections, the surface gradient of the glaciers, the varying position of the site of maxi­ mum ice thickness along the valley profile in the history of the growth and decline of the glacier, and the fact that a valley glacier, unlike a river, has a point of maximum volume and then declines in thickness to its terminus. More recently Matthes 19 finds that in the region of the Yosemite, California, cross-walls, glacier stairways, and roches moutonnees are all

17 R. S. T a r r : Watkins Glen-Catatonk Folio, No. 169, U. S. Geol. Survey, 1909, Field Edition, p. 190. 18 W. H. Hobbs : Characteristics of existing glaciers. New York, 1911, pp. 59-63. W. D. Johnson : M aturity in Alpine glacial erosion. Jour. Geol., vol. 19, 1904, pp. 570, 571 and 574, 575. A. Penck: Glacial features in the Alps. Jour. Geol., vol. 13, 1905, pp. 1, 8, 9, 15. 19 F. E. Matthes : Geologic history of the . U. S. Geol. Survey Prof. Pap. 160, 1930.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 GLACIEE STAIRWAY AND PATER NOSTER LAKES 591

the products of “selective” glacial erosion at points where monolithic, hence obdurate, granitic masses are interposed between much jointed, hence quarriable rock. The fracture-free monoliths, according to Matthes, yield only in negligible amount to glacial abrasion; the effec­ tive, plucking process of glacial sculpture operates solely on closely jointed rock. He maintains, also, that the cross-walls, or risers, of the glacier stairways are fixed in position—that they do not migrate toward the head of the valley. In the Yosemite, where, in places, “joints are altogether lacking for hundreds and even thousands of feet and the rock is wholly undivided,” Matthes’s conclusion, that such conditions fix the sites of the cross-walls there present, seems warranted. He is, nevertheless, constrained to infer considerable jointing (page 93) in rock masses that were glacially ex­ cavated at sites where the rock now exposed is notably massive. He points out that the type of rock involved varies extremely in structure, and that the excavated portions may have been closely jointed. If this relationship existed at one place, it may also have affected glacial sculpture at other points in the Yosemite region. The glacially excavated basins are interpreted as modifications of a preglacial, river-cut canyon. From Matthes’s diagrams (figure 30) it appears that the depth of glacial excavation varied between 1500 and 250 feet. Even if the glacial ex­ cavation did not go deeper than the minimum depth of 250 feet, that measure of erosion by the ice would be enough to permit the glacial proc­ esses to be let down from an easily quarriable rock structure to an un- quarriable mass below. Otherwise stated: if both the deeply excavated areas and the cross-walls are now, in places, on unquarriable rock, why infer that such structural condition is more indicative on the one kind— cross-wall—than on the other kind—deeply excavated—of site? In Matthes’s figure 15—a bird’s-eye view of the Yosemite Valley in the immediately preglacial canyon stage—it is clearly indicated that the gradient of the valley floor was then much interrupted by declivities, both small and great. These declivities had to be eliminated by glacial action or converted (through retreat?) into the great walls (risers) of the glacial stairway, as, for example, at Vernal Falls. In other words, at each step (cross-wall) the glacier quarried directly up to the massive rock. To the cliff (riser) of Vernal Falls notably, there still clings a large fragment of a vertical rock sheet that clearly tells the story (Matthes, page 98). One is led, however, to wonder whether there is not also un­ revealed jointing in the rock of the step above, which is said to be of mono­ lithic massiveness. Indeed, the presence of the fragment of the vertical

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 592 0. D. VON ENGELN ----PALISADE GLACIER

rock sheet suggests that the wall was retreating and that its present posi­ tion is due to the fact that the glacial quarrying stopped because the ice disappeared and not because the glacier, when it existed, was incapable of plucking the wall face. It is also a question whether one should accept the implication of Matthes’s Figure 33 that roches moutonnées require for their development the presence of obdurate bosses of rock between abundantly jointed rock. Certainly, the characteristic roche moutonnée shown in Figure 9 of the present paper, carved from Sierra granite, shows close-spaced jointing in all its parts. As Matthes does not notice the papers by Penck and by Ljunger referred to herein, it is not possible to determine what importance he considered these contributions to have in the problem of glacial sculpture in the Yosemite. To summarize: It appears that the various explanations heretofore presented are not adequate for a systematic and complete understanding of the geomorphology of the site of the Palisade Glacier and of the valley of the North Fork of Big Pine Creek, down which descended the former great glacier that had its head in the cirque basin of the Palisade Glacier. THE CIRQUE The great cirque in which the two parts of the Palisade Glacier rest is terminated down-valley by a great “cross-wall” (figure 4) of rock. Such a wall, according to Penck,20 is a feature that will normally be present below the cirque amphitheatre, and it marks the end, or head, of the excavation of a trough by the valley glacier. On the floor above it the last remnants of glaciation persist. These small glaciers, by sapping action according to Johnson’s description, and also under the conditions outlined by Bowman,21 develop a reversed slope—that is, one which has a down-grade toward the cliffs of the mountain head-wall. At the head- wall are developed gmall kars, or corries, which are to be distinguished from the larger cirque basin of which they are a part and which, as a whole, antedates them. “After having climbed over the walls of the trough’s end,” writes Penck, “one arrives at a flat, formerly occupied by a hanging glacier, usually surrounded by cliffs. Then one arrives at a corrie or series of corries. An ascent of the walls of a corrie always leads one to the crest of mountains.”

20 Op. cit., pp. 15, 16. 211. Bowman : The Andes of Southern Peru. New York, 1916, pp. 296-305 and fig. 197.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 GLACIER STAIRWAY AND PATER NOSTER LAKES 593

Bowman’s exposition of the initiation of the cirque hollow was antici­ pated in part by suggestions in a paper by the Chamberlins.22 In par­ ticular (pages 210-2 1 1 ), they indicate that the absence of the berg- schrund, a point that troubled Bowman (op. cit., pages 205-206, 304-305), is not significant, because the bergschrund and the sapping processes it fosters are sequential to cirque-initiating conditions that were previ­ ously effective. Bowman’s discussion reaches a similar conclusion but does not develop the sequential relationship. At the line of division between stationary, protective snow, and moving, abrasive snow-ice, a scar develops. For a considerable period the snow surfaces above it may remain continuous. But as an excavation is made by the abrasive process at the site of the scar, the part of the catchment basin under the moving ice is deepened, the line of parting between it and the inert snowbank becomes pronounced and is sharply defined, with the result that even­ tually a bergschrund opens. Thereafter, influences due to the existence of the bergschrund accelerate the sapping action at its base. However, independent of the diurnal changes of temperature that are possible be­ cause the bergschrund opens to the air, the physical conditions at the basal line of parting are of such nature that the sapping action must con­ tinue to be very effective. The temperature of the ice there will be slightly less than 0°C. as a maximum because of the pressure from the overlying mass; hence, any water that penetrates to this level will freeze. In the High Sierra the foot of the cirque wall is indicated particularly as the place where water from precipitation on the slope to the west of the scarp crest, percolating through joint fissures, will emerge. Its freezing at the outlet will tend to pry out joint blocks, and, as pointed out by the Chamberlins (op. cit., page 212), the sapping may proceed slightly downward, following in reverse the direction taken by the water in its outward flow. Another factor of importance emphasized in the Chamberlin paper, and recently elaborated upon by Ljunger,23 is the relation between the cohesive and the adhesive strength of the ice. Prom common expe­ rience in attempting to clear dry, solidly frozen ice from concrete and stone pavements it is evident that the cohesive strength of the ice is less than that of its adhesion to the rocky materials. Hence, if the cohesive strength of a prism of the moving ice suffices to pull a joint block loose from its position in the rock mass, the adhesion will be adequate to insure

22 R. T. and T. C. Chamberlin: Certain phases of glacial erosion. Jour. Geol., vol. 19, 1911, pp. 193-216. 23 E. Ljunger : Spaltentektonik und Morphologie der schwedischen Skagerrack-Kiiste. Geolog. Instit. Univ. Upsala Bull., vol. 21, 1930, pp. 291-293.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 594 O. D. VON ENGELN ----PALISADE GLACIEE

the forward movement of the fragment. Again, tension promotes freez­ ing, so that wherever there is a tendency to motion away from the foot of the rock wall, there is also a firming of the ice and a stronger ad­ hesion. Although he does not develop the point, G ilbert24 notes that at a late stage in the excavation of cirques a definite line separates a cliff above from a gentler slope below. That line, Gilbert conceives to mark the base of the bergschrund. Below it the ice-abraded and ice-plucked slope is the site where, after a certain measure of downward excavation by sapping has been wrought, there develops a downward, as well as a forward, mo­ tion of the ice. The conditions that Gilbert suggests appear to be a duplication of those giving rise to the cross-wall at the head of the valley trough, developed when glaciation extended beyond the confines of the cirque basin.

RETREAT OF THE CROSS-WALL

When the glacier of the Palisade basin was of slightly greater volume than it is now, movement of the ice extended over and down the slope of the cross-wall which is the most conspicuous feature in Figure 4. In that phase the glacial chutes were dug. When a still greater volume of ice was being furnished, the whole front of this cross-wall slope was covered by the glacial stream. Then, a series of parallel transverse crevasses in the ice would mark its site. As pointed out in the Chamberlin paper (op. cit., page 213), such a slope and the resulting transverse crevasses entail a break in the con­ tinuity of the glacier motion, hence the beginning of a new motion in the ice mass below at the bottom of the slope. Under these circumstances the erosive processes effective on the front of the cross-wall are quite analogous to those on the part of the cirque wall below the schrund line. There will be tension, freezing, and adhesion of the ice, and dragging out of blocks. In addition, there is present here in maximum degree a situa­ tion that Ljunger (op. cit., page 265) considers to be the most favorable of all for glacial erosion by plucking—namely, a forward thrust by the moving ice with no rock mass ahead to support or oppose the quarrying of blocks from the brink or face of the slope. Such action is not con­ fined to removal of pieces outlined by previously existing fissures. Every projecting angle of the rock affords an opportunity for the ice to break away conchoidal spalls. Where large blocks are broken out, imperfect

24 G. K. Gilbert: Systematic asymmetry of crest lines in the High Sierra of California. Jour. Geol., vol. 12, 1904, p. 582.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 GLACIER STAIRWAY AND PATER NOSTER LAKES 595

roche moutonnée forms are developed; these tend to be rounded by later spalling and abrasion, even on their plucked, downstream, leesides. Ultimately, the backward erosion wrought on the cross-wall declivity should eliminate this steep slope and make the head of the glacial trough coincident with the wall at the head of the cirque. But while the cross-

F ig u r e 10.— Galiano Glacier, Yakutat Bay, Alaska Trough has been excavated to glacial grade to cirque head-wall.

wall is retreating, the sapping processes at the head of the cirque are also effective, and the pursuit is a stern chase, proverbially a long one. At one site known to the writer—the Galiano Glacier, Alaska (figure 10)—this result seems to have been achieved. The rock of the Galiano basin is an easily eroded sandstone, and declivities that originally existed in its floor were apparently erased very quickly, so that the glacial trough now extends without break of slope on the surface of the glacier, right up to the mountain head-wall.

ORIGIN OF THE CROSS-WALL The processes described above apply to the fact and manner of retreat of the cross-wall; they do not afford any explanation of its presence. On the subject of the origin of the cross-wall, Penck’s 25 application

25 A. Penck : Glacial features of the Alps. Jour. Geol., vol. 13, 1905, p. 9.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 596 0. D. VON ENGELN—-PALISADE GLACIER

of the rule of adjustment of valley cross-section to the rate of glacial flow appears to satisfy every requirement. He points out that the con­ fluence of the “slope” glaciers from the cirque basin demands that there be an increase in velocity at the mouth of the cirque to permit continuous movement. Such increased velocity will then act on the glacier bed to deepen it until the rate of flow is equalized with that of the slope glaciers. He calculates that such depth theoretically will be 57 per cent greater

F ig u r e 11.— Pater noster Lakes and Rock Steps in North Fork of Big Pine Creek Valley View is from cross wall at head of the valley trough and below the cirque basin of Palisade Glacier.

than that at the semicircle from which the glaciers come. Accordingly, there should develop at the edge of the semicircle a declivity leading to a trough of adequate dimensions below. The same process is operative with the same results where “dimples” and “exudation basins” or “feeder basins” appear at the heads of the overflow glaciers, along the margin of the Greenland ice sheet; and at the sites of “glint” lakes and “scape colks’” where the Pleistocene ice of Scandinavia moved through gaps in the escarpment facing the west

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 GLACIER STAIRWAY AND PATER NOSTER LAKES 597

coast.26 The differential erosion due to increase in volume and in rate of flow at these places accentuates an initial declivity until the cross- section is adjusted by deepening to provide for the escape of the ice with a uniform rate of flow. Then differential erosion should cease. The adjustment of the cross-section does not, however, prevent the further retreat of the cross-wall in the manner described above.

BASINS AND STEPS BELOW THE CROSS-WALL The reason set forth by Penck for the origin of the cross-wall at the head of the glacial trough does not specifically explain the presence of a series of steps with treads that are commonly the sites of lakes and with risers consisting of steep rock walls—the phenomenon that is so perfectly developed (figures 2 and 11) in the trough valley of Big Pine Creek and is a characteristic feature of nearly all the glaciated valleys of the High Sierra. To account for these steps and basins, Penck makes further applica­ tion of his rule of adjusted cross-sections. He points out that where a tributary glacier comes in, there must be an increase in depth or in width of the main trough if the rate of flow is to remain the same above and below the junction. It would, perhaps, be more accurate to say that there will be an increase in the rate of flow and a thickening of the ice, particularly up-glacier, in the main valley until deepening of the trough, due to these conditions, offsets their effects on the motion and thickness of the ice. He argues, further, that the bottom of the trough at such sites can have a reversed slope as long as the forward surface slope of the glacier is considerably greater than that of the reversed rock slope at the bottom. A third point he makes is that the glacial trough develops uniformly only in homogeneous rocks, and that steps and a narrower, deeper trough develop in consequence of the presence of highly resistant rocks. Finally, he refers to the fact that the valley glacier has a maximum volume, hence maximum erosive effectiveness, at or near the névé line, and that the volume diminishes progressively, if not uniformly, to zero at its terminus. Hence, the slope of the rock bed under the lower end of a glacier may be reversed, provided that in a series of cross-sections of the glacier, diminishing toward its end, the surface of the ice is indicated as so steep that the line of the center of gravity shows a continuous descent. In general, other writers who dis­ cuss this phenomenon refer to Penck, or content themselves with ascrib­

* W. H. Hobbs: Characteristics of existing glaciers. New York, 1911, 1922, pp. 132- 137; gives further details and cites specific observations.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 598 0. D. VON ENGELN— PALISADE GLACIER

ing the development of the glacial stairway to differences in joint- structure and in the nature of the rock that was excavated. All the factors enumerated by Penck are unquestionably significant. However, no tributary glacier of sufficient size to be of any consequence joined the glacial trough of the fork of Big Pine Creek below Palisade Glacier; the trough does not vary in width significantly; and its whole length is carved in essentially similar rock material—granite, with a small inclusion of diorite and gabbro just below the lake farthest down the valley. Hence, it would appear that the development of the glacial staircase is not finally dependent on these exterior and fortuitous circumstances and conditions; that instead, it is a normal phase in the process of en­ largement and deepening by glacial erosion of a valley that was origi­ nally opened by stream erosion. Where glaciation is initiated in moun­ tains of the middle latitudes, stream valleys will normally be in the stages between youth and maturity. Their longitudinal profiles will show steep descents for the whole length of what the British term the mountain track of the stream. On the other hand, the final effect in the excavation of the glacial trough is the development of a low gradient of its bottom. Hobbs,27 quoting Nussbaum,28 shows clearly the fact of this marked difference between the longitudinal profiles of stream valleys and glacial troughs but gives no indication that such difference is significant for interpretation of glacial step development. The longitudinal profile of a mountain stream valley is wholly un­ suited to the accommodation of a valley glacier. The stream has small volume, great fluctuations, and swift flow ; the glacier has great volume and slow rate of flow. Therefore, every excessively steep declivity in the bed of the stream valley, independent of variations in the rock structure, will be a site for the development of roches moutonnées. On these the contrasted kinds of glacial erosion—abrasion on the stoss side, plucking on the lee side—as postulated for the retreat of the cross-wall at the head of the glacial trough, will be effective. I t is indicated also, from the fact that the treads below the risers lengthen as one goes down-valley, that minor declivities present in the original stream valley are normally eliminated by glacial action. Their plucked fronts retreat until they disappear by merging with the reversed slope of the more deeply ex­ cavated tread below a greater declivity up-valley. In this manner, a series of major declivities are developed. The sites for these greater

27 W. H. Hobbs: Characteristics of existing glaciers. New York, 1910, p. 68, fig. 31. 28 F. Nussbaum : Die Täler der Schweizeralpen, Bern, 1910, pi. 3.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 GLACIER STAIRWAY AND PATER NOSTER LAKES 599

risers will probably be determined by the ratio between the rate of glacial erosion and the volume of rock to be excavated and, in some degree, by variations in the rock structure. As long as the glacial occupation of the valley persists in maximum volume, the risers of the several rock steps must continue to retreat. The ultimate effect should be the complete elimination of the rock steps in the trough. Their vertical measure would then serve to increase the height of the wall at the cirque head, as in Figure 10. Where the rock structure is only little resistant to the glacial processes, as in the Galiano Glacier valley and in the. Lauterbrunnen valley, Switzerland, this result may be accomplished rather rapidly. Where, however, the rock is pre­ vailingly granite, or its equivalent in resistance, as in the High Sierra, the steps persisted throughout the period of glaciation. The broad extent of the west slope of the Sierra highlands, with elevations high enough for glaciers, and, in consequence of these conditions, the large volume of rock subject to excavation there before a uniformly graded glacial trough could be cut, account for the remarkable development of the phenomenon of glacial steps and lakes in those areas. In the above discussion it has been assumed that the maximum extent of glaciation in a particular valley persisted until its rapid extinction. Such a history would, however, be exceptional. During the advance and retreat of the ice tongue, intermediate stages probably would be maintained over considerable periods. In accordance with Penck’s formulation, these differences in the volume and length of the glaciers would result in the concentration of maximum erosion at different places in the length of the valley. Recurrent glacia­ tions would still further complicate the problem of accounting for the distribution of the steps and lakes left at the close of glaciation. Despite these complications, it may be expected that the steps will be closer spaced and steeper near the head of the valley, as is true of those in the Big Pine Creek valley. This conclusion follows from the fact that the origi­ nal stream gradient would be flatter in the lower end of the valley, and would, accordingly, have fewer declivities to initiate the development of glacial steps; and from the fact that, because of the low gradient, the depth of rock subject to excavation in reaches at the lower end of a valley is not sufficiently great to provide the vertical element necessary for •pronounced steps at short intervals.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/44/3/575/3430356/BUL44_3-0575.pdf by guest on 26 September 2021