THE CONTRIBUTION OF LANDSLIDES TO LANDSCAPE EVOLUTION IN THE PAONIA-MCCLURE PASS AREA, COLORADO, USA

Mass movement can be activated by earthquakes, rapid snowmelt, or intense rainstorms in concert with gravity. Whereas mass movement plays a major role in the evolution of a hillslope by modifying the morphology of the slope and transporting material from the slope to the valley, such movement is also a potential natural hazard. Studying the morphology of hillslopes and the stream channels, and determining the frequency and magnitude of landslides are fundamental to understanding the role of landslides in landscape evolution and hazard assessment.

We mapped 735 (<160,000 m²) shallow landslides in the Paonia to McClure Pass area of western Colorado. These data were used to determine the relationships of frequency and magnitude of the landslides, and to prepare a map of susceptibility to landslides. In addittion, longitudinal profiles of stream channels in this area were evaluated to understand the relationships between the density of landslides and the concavity of each channel.

The frequency-magnitude of the landslides in Paonia-McClure Pass area are related by a double pareto equation with values α = 1.1, and β = 1.9 for the exponents. The total area of landslides is 4.8×10⁶ m² and the total volume of the landslides is 1.4×10⁷ m³. The areas (A) and the volumes (V) of landslides are related by V = 0.0254×A^1.45. The frequency-magnitude analysis shows that landslides with areas ranging in size from 1,600 m² - 20,000 m² are the most potentially hazardous landslides in the study area. These landslides are the most frequent and also do a significant amount of geomorphic work.

A logistic regression approach was employed to develop a model of mapping landslides. The model predicted 86% of the observed landslides. Most of the observed and predicted landslides were located along the edges of the upland plateaus and inner gorges of the North Fork of the Gunnison River and associated tributaries.

Characteristics of the stream channels in the study area were evaluated by plotting local slopes vs. the drainage area. The study shows that the channels in the basins, consist of a large number of landslides, are convex in nature.