Denali National Park and Preserve, Geologic Resources Inventory Report

Geologic Resources Division

This report accompanies the digital geologic map for Denali National Park and Preserve in Alaska, produced by the Geologic Resources Division in collaboration with its partners. It contains information relevant to resource management and scientific research. This document incorporates preexisting geologic information and does not include new data or additional fieldwork. Denali National Park and Preserve covers more than 6 million acres and features a vast and varied geological landscape. The park protects large portions of the long, arcuate Alaska Range—including Mount McKinley (known as “Denali” [“The High One”] in the native Athabaskan language), which has the greatest vertical relief of any mountain on Earth. The active tectonic processes of southern Alaska are still uplifting the mountains along the Denali fault system. Countering this uplift are weathering and erosion of the highlands by wind and water. Like much of Alaska, the whole of Denali National Park and Preserve is composed of accreted terranes—where the Pacific plate, acting like a conveyor belt, has been bringing bits of islands, the ocean floor, and slivers of other continents northward to for hundreds of millions of years forming a “jigsaw puzzle” of these terranes. The compositions, structures, metamorphic grades, and fossils of these terranes set them apart from neighboring rocks separated by discrete faults. The terranes are covered with more recent sedimentary deposits, and are studded with igneous intrusive rocks. Glacial ice covers a significant amount of the surface area of Denali National Park and Preserve; glaciers carve through thousands of meters of sedimentary, metamorphic, and igneous rocks exposed within the park, creating wide U-shaped valleys and transporting vast amounts of sediment. These glaciers flow over 40 km (25 mi), descending more than 4,500 vertical meters (14,800 ft) from the highest peaks of the range to the lowland hills below. The size, climate, isolation, and complexity of the park’s geologic setting create both a challenge to scientists hoping to understand the environment and a valuable target for preservation of a pristine ecosystem. Understanding the geology in south-central Alaska leads to an appreciation for the unique relationship between geology and the environment. Geologic processes give rise to rock formations, topographic expression, surface and subsurface fluid movement, and soils; thus, geologic units hold clues to the history of the area. Man-made disturbances at the park are also significant. River terraces and channel deposits were reworked during mining periods, locally altering the topographic expression of the landscape and threatening riparian zone health. Human developments may have altered the fragile permafrost regime; as well, glaciers are shrinking due to climate change. Denali National Park and Preserve’s Resource Stewardship Strategy for 2008-2027 identified several geologic processes, values, and components fundamental to achieving the park’s goals and maintaining its significance. The following are critical geologic issues for park management: • Glacier Issues. Today, glacial ice covers approximately 17% of the park. Glacier processes are incredibly dynamic and have far-reaching effects. Resource management concerns include interactions with the changing climate (manifested as glacial thinning or surging glaciers) to visitor safety on glacial surfaces and unstable glacial deposits. The aerial photographic record of glaciers at Denali is extensive, providing an important tool for evaluating glacial changes. Glaciers carved vast valleys and deposited thick mantles of unconsolidated sediment on park slopes, which are vulnerable to slope processes and susceptible to intense erosion. Continual monitoring of the “state of health” of the park’s glaciers would help resource managers understand both the past and future conditions of the glaciers. Seismicity.

Denali National Park and Preserve, Geologic Resources Inventory Report

Collections