Instability leading to channel initiation occurs when advective processes dominate diffusive processes in the transport of surface material. Smith and Bretherton's (1972) linear treatment of this stability/instability phenomenon is here reexamined. Slopes of finite length are considered and a turning point analysis is used to construct a full asymptotic solution for the short wavelength limit. The analysis shows that the initial longitudinal profiles of marginally unstable surface incisions are deepest at a point corresponding to the convex/concave boundary in the base state profile and may actually extend upslope some distance from that point. The extent of the upslope incision is dependent upon the diffusion coefficient for the surface material and the wave number of the disturbance. In the original stability model, the growth rate of the short wavelength instability increases with decreasing wavelength, so that the shortest wavelengths are the most unstable. By introducing a surface material transport function which accounts for microscale nonlocal transfer, the shortest wavelengths are damped and the unstable growth rates are largest at moderate values of the wave number. The lengthscale set by nonlocal material transport represents the spatial scale at which the continuum description underlying the stability model breaks down. The neutral stability diagram for slope length‐wave number space illustrates that when the very shortest wavelengths are damped, concave slope segments may exhibit stability, at least while the system is within a linear regime. The most promising field application of the linear model lies in the characterization of shallow surface incisions, such as rills, which are in initial stages of development.

A zero Reynolds number approximation to the Orr–Sommerfeld equation is used to assess the effects that viscosity stratification has on the stability of a very viscous flow on an incline when surface tension is negligible. Results indicate that for a two-layer system with uniform density, the flow is always unstable when the viscosity of the upper layer is greater than that of the lower layer, regardless of the thickness of the upper layer. The wavenumber of the fastest growing mode is on the order of the inverse of the thickness of the upper layer, implying that the instability is manifested in waves having finite wavelength, whereas previous research on this topic has focused on a long wavelength approximation. It is further shown that neutral stability is independent of the angle of inclination of the underlying slope, although the growth rate of any instability is not. The results suggest that the transverse surficial ridges, which commonly occur on the surfaces of rock glacier forms, may be the product of a flow instability arising from the differing viscosities of the layers that comprise such features.

The stability of a low Reynolds number flow on an inclined plane is investigated with respect to modelling the initiation of transverse wave-like ridges which commonly occur on the surfaces of rock-glacier forms. In accordance with field observations indicating the presence of stratification in rock glaciers, two models of rock-glacier structure are considered, each stratified and possessing a lower layer which is treated as a Newtonian fluid. An upper, less compliant layer is treated, alternatively, as a Newtonian fluid of viscosity greater than that of the lower layer, or as an elastic solid under longitudinal compression induced by a decrease in the slope of the underlying incline. A linear stability analysis is used to examine the behaviour of each of the proposed models, and both are found to generate instabilities at wavelengths comparable to those associated with transverse surficial ridges on rock glaciers. The growth rates of a flow disturbance predicted by the viscous-stratified model appear to be too slow to account fully for the development of wave forms of finite amplitude, suggesting that other mechanisms are involved in the amplification of an initial disturbance. The results of the stability analysis of the elastic lamina model indicate that finite surficial ridges may develop on rock glaciers as a product of a buckling instability in the surface region if there is a decrease in the slope of the underlying incline. Both of the analyses illustrate that transverse ridges can occur on the surface of a rock glacier in the absence of any variations in debris supply to the system. The results further imply that the use of these features in the paleoreconstruction of Holocene climatic conditions must entail an assessment of the relative roles of external climatically driven forcingversusinternal Theologically derived instability.

The stability of a low Reynolds number flow on an inclined plane is investigated with respect to modelling the initiation of transverse wave-like ridges which commonly occur on the surfaces of rock-glacier forms. In accordance with field observations indicating the presence of stratification in rock glaciers, two models of rock-glacier structure are considered, each stratified and possessing a lower layer which is treated as a Newtonian fluid. An upper, less compliant layer is treated, alternatively, as a Newtonian fluid of viscosity greater than that of the lower layer, or as an elastic solid under longitudinal compression induced by a decrease in the slope of the underlying incline. A linear stability analysis is used to examine the behaviour of each of the proposed models, and both are found to generate instabilities at wavelengths comparable to those associated with transverse surficial ridges on rock glaciers. The growth rates of a flow disturbance predicted by the viscous-stratified model appear to be too slow to account fully for the development of wave forms of finite amplitude, suggesting that other mechanisms are involved in the amplification of an initial disturbance. The results of the stability analysis of the elastic lamina model indicate that finite surficial ridges may develop on rock glaciers as a product of a buckling instability in the surface region if there is a decrease in the slope of the underlying incline. Both of the analyses illustrate that transverse ridges can occur on the surface of a rock glacier in the absence of any variations in debris supply to the system. The results further imply that the use of these features in the paleoreconstruction of Holocene climatic conditions must entail an assessment of the relative roles of external climatically driven forcing versus internal Theologically derived instability.

The Rocky Mountain region is one of the most topographically distinct and impressive parts of North America. The Rocky Mountains rise abruptly above the bordering regions, particularly on the east and northeast where they are flanked by plains, less so on the west and southwest where they are bounded by high plateaus. The Rocky Mountains comprise more than 100 individually named ranges that form a belt extending for slightly more than 5,000 km, from near Santa Fe, New Mexico, on the south to the Bering Sea on the north (Fig. 1). The belt varies in width from less than 100 km in the Canadian Rockies to nearly 600 km in the Middle Rockies of Wyoming and northeast Utah. The summits of the ranges rise 1,500 to 2,100 m above adjacent lowlands, to heights 1,800 to 4,400 m above sea level. The Southern Rockies of Colorado have the greatest amount of area, between 3,300 and 4,400 m, and the highest peak, Mount Elbert (4,400 m). The largest area of low mountains is in the Northern Rockies of Idaho and Montana, where summits are commonly only 2,100 to 2,400 m above sea level. A substantial part of the Rocky Mountain region consists of lowlands, in the form of basins and fault-bounded troughs and trenches that lie between ranges. The Rocky Mountain Trench is perhaps the most spectacular fault-bounded lowland, even if it is not the most representative. It extends north from Flathead Lake, Montana, more than 1,500 km, and forms