GLACIAL FEATURES OF DENALI N.P., ALASKA RANGE
FIELD TRIP STOPS – RESULTS OF GLACIAL SCULPTING
LOCATION: South Alaska about 230 miles north of Anchorage
GEOLOGIC FEATURES: Hanging Valley; U-Shaped Valley; Arete; Cirque; Horn; Braided Streams.
DESCRIPTION: Mt. McKinley in Denali N.P. (formerly called Mt. McKinley N.P.) is the tallest peak in North America, reaching 20,310 ft, and growing. Its local relief of about 18,000 ft is the highest in the world. Denali N.P is renowned for its glacial features, some of which are illustrated here. The last phase of glacial sculpting occurred during the Wisconsin Glaciation which reached a maximum at 15-20,000 years ago. Since the Pleistocene had nearly 20 Glacial / Interglacial cycles, the Wisconsin did the final resculpting of the landscape, continuing to form the Cirques, Aretes, Horns, and U-Shaped Valleys that we see today.
(1) Describe what is meant by glacial/interglacial cycles of the Pleistocene?
(2) Differentiate an Arete from a Horn.
(3) CHALLENGE: What natural phenomena are thought to have combined to account for the cyclic nature of glaciation and then warming? (Hint: Milankovitch Cycles.)
-Harris, A. and E. Tuttle. 1983 (3rd ed.). Geology of the National Parks. Kendall/Hunt Publishing Company. Dubuque, IO. 554 pp.
-Harris, D.V. and E.P. Kiver. 1985 (4th ed.). The Geologic Story of the National Parks and Monuments, John Wiley and Sons, New York, 464 pp.
Figure 1 - Getting a glimpse of Mt. McKinley's peak can be quite frustrating as it is often covered by clouds. and fog. Here we get a look at the briefly exposed peak within the central Alaska Range. (Photo 1973)
Figure 2 - Mountain glaciers emerge from Cirques, carving U-shaped Valleys separated by sharp Aretes
Figure 3 - Hanging Valley between two Aretes found just outside the park boundary en route to Anchorage.
Figure 4 - Braided Streams carry glacial meltwater. Braid Bars composed of coarse sediment separate the network of channels