FRACTAL CHARACTERISTICS OF THE ALASKA CONTINENTAL DIVIDE

We have performed a detailed geometric analysis of the Alaska Continental Divide, digitizing the Divide trace from 1:250,000 topographic maps with point spacing of 0.5 km or less. Thirty-one sections of the Divide can be identified based on geomorphic criteria, ranging in standardized length from 30 to 80 km. Each section of the Divide was analyzed by the divider method to evaluate its fractal geometric characteristics.

Richardson plots for the 31 sections show 17 cases having one linear segment and 14 cases having two linear segments with significantly different fractal dimensions (D). Cases with one or two linear segments tend to be grouped together along the Divide. In cases with two linear segments the lower D values are typically found at a larger scale of wandering, whereas the larger D values are found at the smaller scale of wandering; the opposite occurs for a few cases. The eastern half of the Alaska Continental Divide traverses along moderately high mountain ranges, fairly continuous ridge lines, with exception of a few steep passes. Divide sections in this area show fairly constant geometry. The western half of the Divide crosses mostly lowland and scattered mountains and shows much more local variation in D values.

Sections of the Divide can be categorized in the following way. Some lowlands with scattered mountains show D values of 1.00-1.07, while transitional sections mixing lowland and moderately high rugged mountain ranges show D values of 1.08-1.09. Sections of continuous, moderately high rugged mountains with extensive glacial features have characteristic D values of 1.10-1.15. Finally, some lowland sections with scattered mountains display much higher D values, 1.16-1.25, than the first group. Drainage patterns may cause this contrast: the lowland sections marked by lower D values characteristically have better integrated drainage systems, whereas those marked by higher D values have very poor drainage and are swampy in nature.