In general, both topographic relief and maximum elevation increase if erosion is most intense within valleys and less intense on the peaks. Alpine glaciers clearly incise. In nonglaciated regions, incision forms when erosion occurs by infrequent large storms while smooth upland topography forms when erosion occurs by frequent small storms [ Chase, 1992]. The high elevation of Tibet is partly responsible for the high intensity of Indian monsoons and even the current global cold climate [ Kutzbach et al., 1993; Molnar et al., 1993]. The cold climate of the Earth in the last 4 million years in turn has caused incision to occur on formerly smooth uplands. Youthful incised geomorphological surfaces have been globally misinterpreted as evidence Late Cenozoic uplift [ Molnar and England, 1990].
Recent incision of an older upland is well documented along the Front Range of Colorado [ Gregory and Chase, 1992, 1994]. A smooth upland surface developed within the Front Range and the adjacent High Plains by 35 Ma following the Laramide orogeny. Paleobotanic evidence at that time indicates that the upland was at its present elevation relative to sealevel. Structural evidence and the slope of ancient alluvial surfaces also indicate that the current relief between the Front Range and the High Plains formed by 35 Ma. The present escarpment of the Front Range and the youthful valleys incised in it are thus not associated with recent tectonics. Rather the climate has changed so that major storms produce large floods which carry sediment well out onto the High Plains. Such floods are a serious enough hazard that highways through incised canyons have signs warning travelers to climb to high ground.