and Preserve (Denali) are a legacy of the region’s geological history and the advance and retreat of glaciers. One of the major influences on Denali’s ecosystems is the Alaska Range, the massive wall of rock, gla-cial ice, and snow running from southwest to northeast across the park’s six million ac...
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.560.8088 http://home.nps.gov/dena/naturescience/upload/Ecological-Overview.pdf |
| Summary: | and Preserve (Denali) are a legacy of the region’s geological history and the advance and retreat of glaciers. One of the major influences on Denali’s ecosystems is the Alaska Range, the massive wall of rock, gla-cial ice, and snow running from southwest to northeast across the park’s six million acres (2.4 million hectares). It towers above and separates the Kuskokwim and Tanana river basins to the north and from the Susitna River lowlands to the south (Figure 1). This mountain barrier creates two major climate zones in the park and dramatic elevation differences. As a result, the ecosystems range from lowlands with taiga forests, braided glacial stream floodplains, and meandering sloughs; to subalpine woodlands, meadows, and scrub tundra; to alpine low-shrub tundra slopes and steep peaks, including Mt. McKinley at 20,320 feet (6,194 m). Geologic History The oldest rocks in the park, collectively called the Yukon-Tanana terrane, were ocean sediments deposited in shallow seas during the Paleozoic era some 300 to 500 million years ago. Later in the Paleozoic and into the Early Mesozoic (100 to 300 million years ago), other terranes, fragments of the larger continental plates, migrated north on the Pacific Plate and attached to the Yukon-Tanana terrane, creating the current jigsaw puzzle of rocks from many depositional environments. During the last 100 million years, the assembled terranes buckled from continu-ous tectonic collision, uplifting to create the present-day topography of the Alaska Range. About six million years ago, a regional uplift that began in the Alaska Range spread north to push up the Outer Range (Mts. Healy, Margaret, and Wright) (Fitzgerald et al. 1993). Around 70 million years ago, alternating warm, near-tropical conditions and cooler, drier periods enhanced erosion and depo-sition in sedimentary basins such as the “During the past two million years, Denali’s history has been characterized by repeated advances and retreats of a massive ice sheet. Landforms such as sculpted valleys, terraces, ... |
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