Quaternary Glaciation of the Southern Sierra Nevada Mountains

Quaternary Glaciation of the Southern Sierra Nevada Mountains

Calif Tervo

27 November 2013

Prepared for ES767 Quaternary Geology

Dr. J. Aber, Emporia State University

Contents:

Abstract

Glacial History

Geology and Topography

West Side GlaciersKern Basin GlaciersEast Side Glaciers

Conclusions

References

Abstract

During the Quaternary Period, the Sierra Nevada Mountains (Sierras) experienced several extensive glacial episodes. The glaciers of the Sierras were not connected with the Wisconsinian continental glacier but formed independently. From Yosemite Park north, these glacial episodes were characterized by westward flowing glaciers fed by large, thick, upland ice fields that had domed caps that did not reflect the covered topography. The ice fields covered the mountains except for a few nunataks. However, from Sequoia Park south, these glacial episodes did not include large ice fields, but, instead, were characterized by glaciers substantially confined to their cirques and canyons and leaving exposed peaks and ridges. This was partially due to lower latitude, but mainly due to topography. The southern Sierras include an additional north-south crest, i.e., the Great Western Divide, and the south-flowing Kern River Basin that provides an additional drainage and divides the precipitation.

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Glacial History

The Sierras experienced at least six major and minor periods of Quaternary glaciation. There is disagreement on the number and names. One source lists them, from oldest to youngest, as:

Glacial Episonde Dates of Occurrence
McGee about 1.5 Ma
Sherwin about 1 Ma
Tahoe about 70-150 Ka
Tioga about 19-26 Ka
Recess Peak about 14-15 Ka
Matthes (Little Ice Age) stadial. about 1250-1900 CE

Table 1: Quaternay Glaciation in the Sierras. (Modified from Hill, 2006, p. 311).

The Sherwood glaciation was likely the largest of the glacial episodes. Large tills containing extremely decayed rocks provide evidence of the Sherwin glaciation. Most other signs have weathered or eroded. The next largest glaciation was the Tahoe, and its polish and striations have also weathered and eroded but are readily recognizable. Slightly smaller still was the Tioga glaciation which reached a peak about 18-20 Ka and than rapidly retreated. The glacier polish and grooves of the Tioga glaciation are relatively fresh and unaltered. The lateral moraines are prominent and terminal moraines are complete except for the breach of the steam The Recess Peak glaciation was much smaller still (Guyton, 1998, pp. 32-40).

James G. Moore and Gregory S. Mack use a compilation of existing works to define the Tahoe glaciation into two stages that range from 140-200 Ka and 42-50 Ka and the Tioga glaciation at 14-25 Ka (Moore et al, 2008). Figure 1 is a portion of a map showing the extent of the Tahoe ice mass during the younger Tahoe stage, 42-50 Ka.

Figure 1: Map of Late Tahoe Glaciation in Southern Sierras


USGS Scientific Investigations Map 2945. Annotations by Calif Tervo

In the southern Sierra Nevada, the Tahoe glaciation is the oldest glaciation for which there is considerable evidence. There is very limited evidence for older glaciations. As can be seen from the map of Figure 1, from the terminus of the Kern Canyon glacier nothward, the glaciers covered about 70 per cent of the area above 3,000 m. The Tahoe glaciation was only slightly more extensive that the Tioga glaciation. The terminal moraines of the Tahoe glaciers are found about 300 m lower than Tioga terminal moraines (Moore, 2008). The recent and current glaciers in the Sierras were formed during the Little Ice Age (1250-1900 CE) (Schultz, 2010, p. 2). During the Little Ice Age, California glaciers advanced and retreated in response to temperature fluctuations and may have reached a recent maximum around 1895 (Guyton, 1998, p.108).

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Geology and Topography

The Sierra Nevada Mountain Range, the largest contiguous mountain range in the contiguous United States, runs roughly parallel to and inland from the California coast. The Sierras, with a width of 80-130 km and length of 650 km, have almost as much area as the Alps. The Sierras are notably warmer in their southern portion. In general, the Sierras are a west-sloping fault block that climbs from less than 100 m in the Central Valley in the west, to an eastern escarpment, the Sierra Crest, with 4,000 m peaks. For the northern portion of the Sierras, the Sierra Crest is also the watershed divide, such that all the precipitation on the west slopes flows westerly and the precipitous eastern slopes are mainly dry. Because there are no intervening mountains of consequence, the Sierras receive moist Pacific Ocean air and extract most of the moisture by orographic lift. Owens Valley and Death Valley lie to the east in the resulting rain shadow.

The Sierras consist of a batholith of Mesozoic plutons resulting from subduction of the Farallon plate under the North American plate in the Cretaceous Period 80-100 Ma. The rock is principally granitic and mainly granodiorite, monzonite, and tonalite (quartz diorite) (Hill, 2006, p. 180). The granitic rock is intruded into metamorphic marine sedimentary rocks and island arc volcanic rocks, both now preserved as roof pendants (Ehlers, 2004, p. 51). The Sierras are rising. Although the age of the batholith is 80-100 million years old, the age of the Sierras as mountains is estimated to be somewhere between 3 to 40 million years old depending upon various theories of their rise, but probably are not more than 10 million years old.

However, in the southern Sierras, the upper Kern River basin drainage begins northwest of Mount Whitney and descends southward. Kern River Canyon, paralleling the Sierra Crest, was initiated by a long fault and, though inactive for millions of years, still contains a hot spring. An east-west oriented ridgeline, the Kings-Kern Divide, defines the northern limit of the Kern River basin. From Triple Divide Peak on the Kings-Kern Divide, a ridge, the Great Western Divide, proceeds southward and defines the west side of the Kern Basin. The north-south disposed Great Western Divide is more than a mere ridgeline as it contains many peaks in the 3,000-4,000 m range and is has no significant gaps. Therefore, it removes substantial moisture. Thus, in the southern Sierras there are three drainages: westward from the Great Western Divide, eastward from the Sierra Crest, and, between these, the Kern River basin. This is an area of spectacular glacial canyons with hanging valley waterfalls, craggy horn peaks, knife-blade arêtes, cirques with snow fields, crystal clear alpine lakes, glacial polish, glacial striations, infinite erratics, tarns, and moraine till.

Figure 2 shows an east-west simplified profile of the southern Sierras from the city of Three Rivers in the Central Valley, curving slightly north and traversing at the Kaweah River canyon, Great Western Divide, upper Kern Canyon, Mt. Whitney and the town of Lone Pine to the Owens River in the Owens Valley. Vertical scale is exaggerated..

Figure 2: East-West Profile of Southern Sierras


© 2013 Calif Tervo (distance and altitude data from Google Earth)

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West Side Glaciers

Photos 1 and 2 are views of portions of the crest of the Great Western Divide from the east, looking across Big Arroyo. On the western side of the Great Western Divide, many glaciers originated near these peaks.

Photo 1: Portion of Great Western Divide (looking west)


© 2013 Calif Tervo

Photo 2: Portion of Great Western Divide (looking west)


© 2013 Calif Tervo

An exemplary western glacier valley is the Middle Fork of the Kaweah River. Photo 3 shows the cirque of the glacier in Eagle Scout Peak (3,670 m) on the Great Western Divide. Precipice Lake (3,150 m) is the tarn in the cirque. The glacier created a series of step lakes as it descended. Photo 4 shows Hamilton Lake (2,570 m), one of the step lakes. The lip of the lake is very hard granite and was smoothed by the glacier. Hamilton Lake occupies a rock bowl where three of four glaciers issuing from cirques 500-700 m higher converged. Further downstream, branch glaciers joined the valley glacier. On the north wall is a spectacular cliff formation called Valhalla. Branch glaciers flowed around these formations, but did not flow over their tops. Generally, the top of the side ridges were nunataks.

Photo 3: Precipice Lake


© 2013 Calif Tervo

Photo 4: Hamilton Lake and Vahalla


© 2013 Calif Tervo

Photo 5 shows another stunning rock formation farther down the valley on the south side. Branch glaciers flowed around these rock formations and smoothed their lower surfaces, but did not flow over their tops. The Middle Fork of the Kaweah River glacier reached a length of about 10 miles and the terminus was at 1,800m. Other nearby glaciers in the valleys of the Marble, East, and South Forks of the Kaweah River terminated at 1,860 m, 1,555 m, and 1,890 m, respectively (Moore, 2008).

Photo 5: South Wall Glacier Cuts


© 2013 Calif Tervo

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Kern Basin Glaciers

The Kern Basin is enclosed on the north by the King-Kern Divide, on the west by the Great Western Divide, and on the east by the Sierra Crest (see Map Figure 1). Kern Canyon is 10 km west of Mt. Whitney on the Sierra Crest and 15 km east of the Great Western Divide. Photo 6 is a view of Kern Canyon looking south from part-way up the west wall at Chagoopa Creek. Kern Canyon was carved by the southernmost trunk glacier in the Sierras (Guyton, 1998, p. 44). Kern Canyon is a classic truck glacier with many contributing branch glaciers. The Kern River glacier terminated at 1,920 m (Moore, 2008).

Photo 6: Kern Canyon


© 2013 Calif Tervo

One of the largest branch glaciers created Big Arroyo. Photo 7 is a view looking south near the head of Big Arroyo. As can be seen in Map Figure1, Big Arroyo, almost 25 km long, is the largest branch glacier along the western periphery of the Kern Basin. Big Arroyo begins at the King-Kern Divide and goes south along the Great Western Divide and then southeast to join Kern Canyon. Big Arroyo was fed by many branch glaciers originating along the Great Western Divide or along the Kaweah Peaks Ridge. The lower shoulders of Big Arroyo are rounded because of overriding by the glacier (Matthes, 1965).

Photo 7: Big Arroyo


© 2013 Calif Tervo

The Chagoopa Plateau, at the juncture of Big Arroyo and Kern Canyon, was invaded by a side lobe of the Big Arroyo Glacier so as to contain a shallow ice field. It is now forested. A moraine from the Chagoopa Plateau ice field dammed Moraine Lake. Photo 8 shows Moraine Lake on a rim of Big Arroyo on Chagoopa Plateau. One of the few lakes dammed by a moraine, Moraine Lake is dammed by a Tahoe moraine that is well timbered.

Photo 8: Moraine Lake


© 2013 Calif Tervo

Immediately west of central Kern Canyon is the Kaweah Basin. Kaweah Basin has a stark beauty composed mostly of rough, treeless, glacier-scoured terrain of peaks, bare granite, cirques, arêtes, and small lakes. Kaweah Peaks Ridge, separating Big Arroyo from Kaweah Basin, was a nunatak. The crest includes rugged and loose metamorphic sedimentary rock and volcanics that were roof pendants to the granitic batholith. Photo 9 of Mount Kaweah shows volcanic rock.

Photo 9: Mount Kaweah


© 2013 Calif Tervo

Photo 10 of Black Kaweah Peak, a roof pendant to the granite batholith, is in the Kaweah Peak Ridge and exhibits very shattered, slatish rock overlying granitic rock (Hill, p. 105).

Photo 10: Black Kaweah


© 2013 Calif Tervo

East Side Glaciers

The eastern escarpment occupies by far the smallest surface area of the drainage areas. Due to its great height, the eastern escarpment had many glaciers, there being a glacier in almost every canyon (Matthes, 1930). However, eastern glaciers tended to be much shorter than the western or Kern Basin glaciers because the eastern escarpment was shorter and steeper, it received less precipitation, the areas at the canyon heads that could gather snowfall were small, and terminal areas were hotter and dryer. Consequently, the east slope glaciers terminated at higher elevations. The altitudes at which Tahoe glaciers terminated increased from north to south, from about 1,800-3,000 m (Moore, 2008). The aridity of the east escarpment preserved the glacial deposits better. Photo 11 shows the east face of Mt. Whitney (4,419 m) on the Sierra Crest.

Photo 11: East Face of Mount Whitney


© 2013 Calif Tervo

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Conclusions

During the Quaternary Period, the Sierras experienced several extensive glacial episodes. Unlike their brethren to the north, the glaciers of the southern Sierras did not commence in thick, ice fields with domed caps, but, instead, were substantially confined to their cirques and canyons. This was partially due to lower latitude, but mainly due to topography in that the southern Sierras include an additional north-south crest, the Great Western Divide, and include the south-flowing Kern River Basin. The steeper west side drainage prevented precipitation from reaching and creating large central ice fields. The Kern Basin created an additional drainage and divided the precipitation into three zones instead of two.

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References Cited

Ehlers, J. & Gibbard P.I (eds.). 2004. Quaternary Glaciations - Extent and Chronology, Part II. Elsevier Science, 450 p.

Guyton, Bill. 1998. Glaciers of California, Modern Glaciers, Ice Age Glaciers, the Origin of Yosemite Valley, and a Glacier Tour of the Sierra Nevada. University of California Press, Berkeley and Los Angeles, California. 223 pp.

Hill, Mary. 2006. Geology of the Sierra Nevada. University of California Press revised edition, Berkeley and Los Angeles, California 468 pp.

Matthes, François E. 1930. Geologic history of the Yosemite Valley (Geological Survey Professional Paper 160). United States Department of the Interior. Accessed from http://www.nps.gov/history/history/online_books/geology/publications/pp/160/.

Matthes, François E. Prepared posthumously by Fryxell, Fritiof. 1965. Glacial Reconnaissance of Sequoia National Park California (Geological Survey Professional Paper 504-A). United States Department of the Interior. Accessed from http://pubs.er.usgs.gov/publication/pp504A

Moore, James G., and Mack, Gregory S. 2008. Map showing limits of Tahoe glaciation in Sequoia and Kings Canyon National Parks, California. 2008. U.S. Geological Survey Scientific Investigations Map 2945, scale 1:125,000 Accessed from http://pubs.usgs.gov/sim/2945/ .

Schultz, Emily. 2010. Glaciers of the Sierra Nevada: Past, Present, and Future. Retrieved from Volcanoes of the Eastern Sierra Nevada: Geology and Natural Heritage of the Long Valley Caldera. Indiana University. Retrieved from http://www.indiana.edu/~sierra/papers/2010/schultz.html.

Other informative works:

Gillespie, Alan R. & Zehfuss, Paul H. Glaciations of the Sierra Nevada, California, USA. In Developments in Quaternary Sciences, Volume 2, Part B, 2004, pp. 51–62. Ehlers, J. & Gibbard P.I (eds.). 2004. Elsevier.

Storer, Tracy I., Usinger, Robert L., & Lukas, David. 2004.Sierra Nevada Natural History: California Natural History Guides, revised ed. 437 pp.

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