About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

Alaska Geological Society

Abstract


Guide to the Bedrock geology of a Traverse of the Chugach Mountains from Anchorage to Cape Resurrection, 1984
Pages 24, 35-40

Abstract: Portage Lake and Glacier

G. R. Winkler1

The following synopsis of what we will see at the Chugach National Forest visitor center at Portage Lake is adapted from Mayo and others (1977).

For centuries the low pass at the head of Turnagain Arm served as a surface transportation route between Upper Cook Inlet and Prince William Sound–prehistorically, for competing interior and coastal native groups, and subsequently for Russian traders and trappers and early miners in the region. During an early geological reconnaissance of the area, Mendenhall (1900) gave the broad, 600-ft divide the name Portage Pass. During the past 200 years, Portage Glacier has advanced and retreated markedly. According to reports from the Vancouver expedition, in 1794 the glacier did not occupy the valley below the pass, but Portage Lake may have been larger than it is today. The glacier then advanced strongly at least 5 km until about 1890, at which time Portage Pass and the lake basin were completely occupied by ice. The low rubbly mounds which impound present Portage Lake are remnants of the terminal moraine left by this advance. In 1898, gold rush prospectors used the pass by climbing over Portage Glacier.

The approximately 4-km retreat of the glacier since at least 1914 has been documented by Barnes (1943) and Schmidt (1961) and apparently continues today, leaving 190-m deep Portage Lake in the glacial depression. Surface access to Portage Pass is difficult because the lake is subject to high winds and may be choked with icebergs, the lower part of the glacier is very crevassed, and the bedrock valley walls are very steep. From observations of pronounced glacial thinning in the terminus area and decreased input from tributary glaciers and from calculations of ice-balance data, Mayo and others (1977) forecast that Portage Glacier will continue to retreat. If it continues at the average rate of retreat since 1914, the terminus will disappear from view at the present Chugach National Forest visitor facility about 2020. However, the rate of retreat has had a sustained dramatic increase since 1970, and the glacier may be out of view from this point much sooner.

References

Barnes, F. F., 1943, Geology of the Portage Pass area, Alaska: U.S. Geological Survey Bulletin 926-D, p. 211–235.

Barry, M. S., 1973, A History of Mining on the Kenai Peninsula: Northwest Publishing Co., 214 p.

Berg, H. C., Jones, D. L., and Richter, D. H., 1972, Gravina-Nutzotin belt-tectonic significance of an upper Meszoic sedimentary and volcanic sequence in southern and southeastern Alaska: U.S. Geological Survey Professional Paper 800-D, p. D1–D24.

Blake, M. C., Jr., and Jones, D. L., 1974, Origin of Franciscan melanges in northern California, in Dott, R. H., Jr., and Shaver, R. H., eds, Modern and ancient geosynclinal sedimentation: Society of Economic Paleontologists and Mineralogists, Special Publication No. 19, p. 345–357.

Budnik, R. T., 1974, The geologic history of the Valdez Group, Kenai Peninsula, Alaska–Deposition and deformation at a Late Cretaceous consumptive plate margin: University of California, Los Angeles, unpublished Ph.D. dissertation, 139 p.

Burk, C. A., 1965, Geology of the Alaskan Peninsula–Island arc and continental margin: Geological Society of America Memoir 99, 250 p.

Byrne, Tim, 1979, Late Paleocene demise of the Kula–Pacific spreading center: Geology, v. 7, no. 7, p. 341–344.

Cann, J. R., 1970, Rb, Sr, V, Zr, and Nb in some ocean floor basaltic rocks: Earth and Planetary Science Letters, v. 10, p. 7–11.

Carden, J. R., Connelly, William, Forbes, R. B., and Turner, D. L., 1977, Blueschists of the Kodiak Islands, Alaska: an extension of the Seldovia schist terrane: Geology, v. 5, no. 9, p. 529–533.

Clark, S. H. B., 1972, Reconnaissance bedrock geologic map of the Chugach Mountains near Anchorage, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-350, 1 sheet, scale 1:250,000.

Clark, S. H. B., 1973, The McHugh Complex of south-central Alaska: U.S. Geological Survey Bulletin 1372-D, p. D1–D11.

Clark, S. H. B., 1981, Guide to the bedrock geology along the Seward highway north of Turnagain Arm: Anchorage, Alaska Geological Society Publication Number 1, 36 p.

Coleman, R. G., 1977, Ophiolites: Berlin-Heidelberg-New York, Springer-Verlag, 229 p.

Coleman, R. G., and Peterman, Z. E., 1975, Oceanic plagiogranite: Journal of Geophysical Research, v. 80, p. 1099–1108.

Connelly, William, 1978, Uyak Complex, Kodiak Islands, Alaska–A Cretaceous subduction complex: Geological Society of America Bulletin, v. 89, p. 755–769.

Connelly, William, and Moore, J. C., 1977, Geologic map of the northwest side of the Kodiak Islands, Alaska: U.S. Geological Survey Open-File Map 77-382, 2 sheets, scale 1:250,000.

Cowan, D. S., 1982, Geological evidence for post-40 Ma large-scale, northwestward displacement of part of southeastern Alaska: Geology, v. 10, no. 6, p. 309–313.

Cowan, D. S., and Boss, R. F., 1978, Tectonic framework of the southwestern Kenai Peninsula, Alaska: Geological Society of America Bulletin, v. 89, no. 1, p. 155–158.

Csejtey, Bela, Jr., Nelson, W. H., Jones, D. L., Silberling, N. J., Dean, R. M., Morris, M. S., Lanphere, M. A., Smith, J. G., and Silberman, M. L., 1978, Reconnaissance geologic map and geochronology, Talkeetna Mountains quadrangle, northern part of the Anchorage quadrangle, and southwest corner of the Healy quadrangle: U.S. Geological Survey Open-File Report 78-558A, 60 p., 1 sheet, scale 1:250,000.

Decker, J. E., 1980, Geology of a Cretaceous subduction complex, western Chichagof Island, southeastern Alaska: Stanford University, unpublished Ph.D dissertation, 135 p.

Decker, J. E., and Plafker, George, 1982, Correlation of rocks in the Tarr Inlet suture zone with the Kelp Bay Group, in Coonrad, W. L., ed., The United States Geological Survey in Alaska–Accomplishments during 1980: U.S. Geological Survey Circular 844, p. 119–123.

Decker, John, Wilson, F. H., and Turner, D. L., 1980, Mid-Cretaceous subduction in southeastern Alaska [abs.]: Geological Society of America, Abstracts with Programs, v. 12, no. 3, p. 103.

Dickinson, W. R., and Suczek, C. A., 1979, Plate tectonics and sandstone compositions: American Association of Petroleum Geologists Bulletin, v. 63, p. 2164–2182.

Dumoulin, J. A., 1984, Composition and provenance of sandstones of the Orca and Valdez Groups, Prince William Sound, Alaska: Geological Society of America, Abstracts with Programs, v. 16, (in press).

Ernst, W. G., 1976, Petrologic Phase Equilibria: San Francisco, W. H. Freeman and Company, 333 p.

Grant, U. S., 1915, The southeastern coast of Kenai Peninsula, in Martin, G. C., Johnson, B. L., and Grant, U. S., Geology and mineral resources of Kenai Peninsula, Alaska: U.S. Geological Survey Bulletin 587, p. 209–238.

Grant, U. S., and Higgins, D. F., Jr., 1909, Notes on the geology and mineral prospects in the vicinity of Seward, Kenai Peninsula, in Brooks, Alfred H., and others, mineral resources of Alaska, report on progress of investigations in 1908: U.S. Geological Survey Bulletin 379, p. 98–107.

Grommé, Sherman, and Hillhouse, J. W., 1981, Paleomagnetic evidence for northward movement of the Chugach terrane, southern and southeastern Alaska, in Albert, N. R. D., and Hudson, Travis, eds., The United States Geological Survey in Alaska–Accomplishments during 1979: U.S. Geological Survey Circular 823-B, p. B70–B72.

Hoekzema, R. B., 1981, Placer sampling and related Bureau of Mines activities on the Kenai Peninsula, Alaska: U.S. Bureau of Mines Open-File Report 138-81, 28 p.

Hsu, K. J., 1968, Principles of melange and their bearing on the Franciscan-Knoxville paradox: Geological Society of America Bulletin, v. 79, p. 1063–1074.

Hsu, K. J., 1974, Melanges and their distinction from olistostromes, in Dott, R. H., Jr., and Shaver, R. H., eds, Modern and ancient geosynclinal sedimentation: Society of Economic Paleontologists and Mineralogists, Special Publication No. 19, p. 321–333.

Hudson, Travis, 1983, Calc-alkaline plutonism along the Pacific rim of southern Alaska, in Roddick, J. A., ed., Circum-Pacific plutonic terranes: Geological Society of America Memoir 159, p. 159–170.

Hudson, Travis, and Plafker, George, 1982, Paleogene metamorphism of an accretionary flysch terrane, eastern Gulf of Alaska: Geological Society of America Bulletin, v. 93, p. 1280–1290.

Hudson, Travis, Plafker, George, and Peterman, Z. E., 1979, Paleogene anatexis along the Gulf of Alaska margin: Geology, v. 7, p. 573–577.

Johnson, B. L., 1912, Gold deposits of the Seward-Sunrise region, Kenai Peninsula: U.S. Geological Survey Bulletin 520, p. 131–173.

Jones, D. L., and Clark, S. H. B., 1973, Upper Cretaceous (Maestrichtian) fossils from the Kenai-Chugach Mountains, Kodiak and Shumagin Islands, southern Alaska: U.S. Geological Survey Journal of Research, v. 1, no. 2, p. 125–136.

Jones, D. L., and Silberling, N. J., 1979, Mesozoic stratigraphy–The key to tectonic analysis of southern and central Alaska: U.S. Geological Survey Open-File Report 79-1200, 37 p.

Karl, Susan, Decker, John, and Jones, D. L., 1979, Early Cretaceous radiolarians from the McHugh Complex, south-central Alaska, in Johnson, K. M., and Williams, J. R., eds., The United States Geological Survey in Alaska–Accomplishments during 1978: U.S. Geological Survey Circular 804-B, p. B88–B90.

Karl, S. M., Decker, J. E., and Johnson, B. R., 1982, Discrimination of Wrangellia and the Chugach terrane in the Kelp Bay Group on Chichagof and Baranof Islands, southeastern Alaska, in Coonrad, W. L., ed., The United States Geological Survey in Alaska–Accomplishments during 1980: U.S. Geological Survey Circular 844, p. 124–128.

Lanphere, M. A., 1966, Potassium-argon ages of Tertiary plutons in the Prince William Sound region, Alaska: U.S. Geological Survey Professional Paper 550-D, p. D195–D198.

Loney, R. A., Brew, D. A., Muffler, L. J. P., and Pomeroy, J. S., 1975, Reconnaissance geology of Chichagof, Baranof, and Kruzof Islands, southeastern Alaska: U.S. Geological Survey Professional Paper 792, 105 p.

Martin, G. C., Johnson, B. L., and Grant, U. S., 1915, Geology and mineral resources of Kenai Peninsula, Alaska: U.S. Geological Survey Bulletin 587, 243 p.

Mayo, L. R., Zenone, Chester, and Trabant, D. C., 1977, Reconnaissance hydrology of Portage Glacier basin, Alaska: U.S. Geological Survey Hydrologic Investigations Atlas HA-583, 2 sheets, scales 1:50,000 and 1:250,000.

Mendenhall, W. C., 1900, A reconnaissance from Resurrection Bay to the Tanana River, Alaska, in 1898: U.S. Geological Survey 20th Annual Report, pt. 7, p. 265–340.

Mitchell, P. A., 1979, Geology of the Hope-Sunrise (gold) mining district, north-central Kenai Peninsula, Alaska: Stanford University, unpublished M.S. thesis, 123 p.

Moffit, F. H., 1905, Gold placers of Turnagain Arm region: U.S. Geological Survey Bulletin 259, p. 90–99.

Moffit, F. H., 1907, Gold fields of the Turnagain Arm region: U.S. Geological Survey Bulletin 277, 80 p.

Moore, G. W., 1969, New formations on Kodiak and adjacent islands, Alaska: U.S. Geological Survey Bulletin 1274-A, p. A27–A35.

Moore, J. C., 1973, Cretaceous continental margin sedimentation, southwestern Alaska: Geological Society of America Bulletin, v. 84, p. 595–614.

Moore, J. C., 1978, Orientation of underthrusting during Latest Cretaceous and Earliest Tertiary time, Kodiak Islands, Alaska: Geology, v. 6., no. 4, p. 209–213.

Moore, J. C., Byrne, Tim, Plumley, P. W., Reid, Mary, Gibbons, Helen, and Coe, R. S., 1983, Paleogene evolution of the Kodiak Islands, Alaska–Consequences of ridge-trench interaction in a more southerly latitude: Tectonics, v. 2, p. 265–293.

Moore, J. C., and Connelly, William, 1977, Mesozoic tectonics of the southern Alaska margin, in Talwani, Manik, and Pitman, W. C., III, eds., Island arcs, deep sea Trenches, and back-arc basins: Journal of Geophysical Research Maurice Ewing Series, v. 1, p. 71–82.

Nelson, S. W., Dumoulin, J. A., and Marti Miller, 1984, Geologic map of the Chugach National Forest, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-1645-B, scale 1:250,000 (in press).

Nilsen, T. H., 1982, Accretion model for the Cretaceous Chugach terrane, southern Alaska, in Coonrad, W. L., ed., The United States Geological Survey in Alaska–Accomplishments during 1980: U.S. Geological Survey Circular 844, p. 93–97.

Nilsen, T. H., and Bouma, A. H., 1977, Turbidite sedimentology and depositional framework of the Upper Cretaceous Kodiak Formation and related stratigraphic units, southern Alaska [abs.]: Geological Society of America, Abstracts with Programs, v. 9, no. 7, p. 1115.

Nilsen, T. H., and Moore, G. W., 1979, Reconnaissance study of Upper Cretaceous to Miocene stratigraphic units on sedimentary facies, Kodiak and adjacent islands, Alaska: U.S. Geological Survey Professional Paper 1039, 34 p.

Nilsen, T. H., and Zuffa, G. G., 1982, The Chugach terrane, a Cretaceous trench-fill deposit, southern Alaska, in Legget, J. K., ed., Trench-forearc geology–Sedimentation and tectonics on modern and ancient active plate margins: London, Blackwells, p. 213–227.

Park, C. F., Jr., 1933, The Girdwood district, Alaska: U.S. Geological Survey Bulletin 849-G, p. 381–424.

Pavlis, T. L., 1983, Pre-Cretaceous crystalline rocks of the western Chugach Mountains, Alaska–Nature of the basement of the Jurassic Peninsular terrane: Geological Society of America Bulletin, v. 94, no. 11, p. 1329–1344.

Pearce, J. A., 1975, Basalt geochemistry used to investigate past tectonic environments on Cyprus: Tectonophysics, v. 25, p. 41–67.

Plafker, George, and Campbell, R. B., 1979, The Border Ranges fault in the Saint Elias Mountains, in Johnson, K. M., and Williams, J. R., eds., The United States Geological Survey in Alaska–Accomplishments during 1978: U.S. Geological Survey Circular 804B, p. B102–B104.

Plafker, George, Jones, D. L., Hudson, Travis, and Berg, H. C., 1976, The Border Ranges fault system in the Saint Elias Mountains and the Alexander Archipelago, in Cobb, E. H., ed., The United States Geological Survey in Alaska–Accomplishments during 1975: U.S. Geological Survey Circular 733, p. 14–16.

Plafker, George, Jones, D. L., and Pessagno, E. A., Jr., 1977, A Cretaceous accretionary flysch and melange terrane along the Gulf of Alaska margin, in Blean, K. M., ed., The United States Geological Survey in Alaska–Accomplishments during 1976: U.S. Geological Survey Circular 751-B, p. B41–B43.

Plumley, P. W., Coe, R. S., and Byrne, Tim, 1983, Paleomagnetism of the Paleocene Ghost Rocks Formation, Prince William terrane, Alaska: Tectonics, v. 2, no. 3, p. 295–314.

Reed, B. L., and Lanphere, M. A., 1972, Generalized geologic map of the Alaska-Aleutian Range batholith showing potassium-argon ages of the plutonic rocks: U.S. Geological Survey Miscellaneous Field Studies Map MF-372, 1 sheet, scale 1:250,000.

Schmidt, R. A. M., 1961, Recession of Portage Glacier, Alaska: U.S. Geological Survey Professional Paper 424-D, p. D202–D203.

Silberman, M. L., MacKevett, E. M., Jr., Connor, C. L., Klock, P. R., and Kelechitz, Georgiana, 1981a, K-Ar ages of metamorphosed Nikolai Greenstone from the McCarthy quadrangle, Alaska–The “docking” of Wrangellia, in Albert, N. R. D., and Hudson, Travis, eds., The United States Geological Survey in Alaska–Accomplishments during 1979: U.S. Geological Survey Circular 823-B, p. B61–B63.

Silberman, M. L., Mitchell, P. A., and O’neil, J. R., 1981b, Isotopic data bearing on the origin and age of the epithermal lode gold deposits in the Hope-Sunrise mining district, northern Kenai Peinnsula, Alaska, in Albert, N. R. D., and Hudson, Travis, eds., The United States Geological Survey in Alaska–Accomplishments during 1979: U.S. Geological Survey Circular 823-B, p. B81–B84.

Silberman, M. L., Madden, D. J., Mitchell, P. A., and Hoekzema, R. B., 1984, Geology and geochemistry of the lode-gold deposits in the Chugach Terrane of western Prince William Sound, southern Alaska: Geological Society of America, Abstracts with Programs, v. 16 (in press).

Stone, D. B., and Packer, D. R., 1979, Paleomagnetic data from the Alaska Peninsula: Geological Society of America Bulletin, v. 90, p. 545–560.

Tuck, Ralph, 1933, The Moose Pass-Hope District, Kenai Peninsula, Alaska: U.S. Geological Survey Bulletin 849-I, p. 469–530.

Tysdal, R. G., and Case, J. E., 1977, the McHugh Complex in the Seward quadrangle, south-central Alaska, in Blean, K. M., ed., The United States Geological Surevy in Alaska–Accomplishments during 1976: U.S. Geological Survey Circular 751-B, p. B48–B49.

Tysdal, R. G., and Case, J. E., 1979, Geologic map of the Seward and Blying Sound quadrangles, Alaska: U.S. Geological Survey Miscellaneous Investigation Series Map I-1150, 12 p., 1 sheet, scale 1:250,000.

Tysdal, R. G., Case, J. E., Winkler, G. R., and Clark, S. H. B., 1977, Sheeted dikes, gabbro, and pillow basalt in flysch of coastal southern Alaska: Geology, v. 5, p. 377–383.

Tysdal, R. G., and Plafker, George, 1978, Age and continuity of the Valdez Group, southern Alaska: U.S. Geological Survey Bulletin 1457-A, p. A120–A124.

Winkler, G. R., 1976a, Reconnaissance geochemistry and tectonics of Gulf of Alaska greenstones, in Cobb, E. H., ed, The United States Geological Survey in Alaska–Accomplishments during 1975: U.S. Geological Survey Circular 733, p. 11.

Winkler, G. R., 1976b, Deep-sea fan deposition of the lower Tertiary Orca Group, eastern Prince William Sound, Alaska, in Miller, T. P., ed., Symposium Proceedings, Recent and ancient sedimentary environments in Alaska: Anchorage, Alaska Geological Society, p. R1–R20.

Winkler, G. R., 1983, The Peninsular and Chugach terranes, southern Alaska–Their composition and timing of their amalgamation [abs.]: Geological Society of America, Abstracts with Programs, v. 15, no. 5, p. 386.

Winkler, G. R., and Plafker, George, 1981, Geologic map and cross sections of the Cordova and Middleton Island quadrangles, southern Alaska: U.S. Geological Survey Open-File Report 81-1164, 26 p., 1 sheet, scale 1:250,000.

Winkler, G. R., Silberman, M. L., Grantz, Arthur, Miller, R. J., and MacKevett, E. M., Jr., 1981, Geologic map and summary geochronology of the Valdez quadrangle, southern Alaska: U.S. Geological Open-File Report 80-892A, 2 sheets, scale 1:250,000.

Zuffa, G. G., Nilsen, T. H., and Winkler, G. R., 1980, Rock-fragment petrography of the Upper Cretaceous Chugach terrane, southern Alaska: U.S. Geological Survey Open-File Report 80-713, 28 p.

Acknowledgments and Associated Footnotes

1 G. R. Winkler: U.S. Geological Survey

Copyright © 2014 by the Alaska Geological Society