Characterization of topographic steady state in Taiwan

Abstract

The arc-continent collision in Taiwan has resulted in surface uplift, high relief and high rates of erosion. Because the collision is older in the north and has propagated southward, Taiwan offers the opportunity to study the evolution of topography as it evolves towards a large-scale steady state. In this paper, we analyze a 40-m digital elevation model of Taiwan to determine how topographic steady state is expressed in the landscape; particular attention is paid to the eastern Central Range, where major drainage basins are approximately aligned in the direction of the collision propagation. Analyses of orogen size, regional topographic slope, drainage basin hypsometry, and local topographic slope reveal a geomorphological transition 100–125 km north of the southern tip of the island. To the south of this transition, topographic characteristics change with distance along the island; to the north, these characteristics are relatively constant, which we interpret as representing large-scale topographic steady state. Assuming that the collision has propagated southward at a rate of 55 mm/yr, the time to topographic steady state is 1.8–2.3 Myr after emergence above sea level. Within the steady state region, we evaluate regional variability in the topography and find that the most prominent deviations from a steady form are associated with large-scale structures, though our analyses of local topographic slope and river profile form suggest that spatial variations in rock strength and rock uplift rate also contribute to regional topographic variability.