Geomorphic altitudinal zonation of the high mountains of Taiwan

The Central Range of Taiwan has the characteristics of a high mountain area: Pleistocene glacial forms, crests exceeding the timberline, and debris slopes produced by frost weathering. Estimated denudation rates for Taiwan have an average of 5 mm/a, and are presumed to be in equilibrium with the uplift rate. These values are derived either from short-term debris measurements in rivers or from fission track dating for a long-term evaluation. A 5 mm/a denudation rate over long timescales seems reasonable, but does not indicate whether this rate operated continuously throughout. Today it is apparent that mass movements and fluvial erosion, triggered by typhoons, are more intense at altitudes below 3000 m a.s.l., and therefore the denudation rate in these altitudes is very likely higher than 5 mm/a. Above 3000 m precipitation is lower. Mass movements are rare, and above 3400-3500 m a.s.l. frost weathering during winter produces debris slopes. Low fluvial activity in the seasonal to episodically occupied stream valleys does not significantly contribute to fluvial erosion. Only in very few places has backward erosion already reached the zone above 3000 m a.s.l., and gravity-related processes are active. Since glacial features are still preserved, the denudation rate is considered to have been lower than 5 mm/a since the last glacial cycle, and denudation in the mountains is not in equilibrium from the top to the lower valleys.