LITHOLOGICAL IMPACTS ON STEP POOLS IN ALPINE STREAMS IN THE SAN JUAN MOUNTAINS, COLORADO: A PRELIMINARY STUDY
The study area is located in the San Juan Mountains of southwestern Colorado. We measured the longitudinal profile and cross-sections, as well as documenting the type of lithology, and channel form. Our sample streams included both step-pool series formed by clasts and step pools in bedrock.
The results from our study suggest that no noteworthy difference appears to occur between a bedrock step-pool series and an in situ step-pool series. Regarding the longitudinal profile of a step-pool sequence, the connection between geometry of the channel, step wavelength of the steps and height of the steps from pool to top of a step is similar to results reported for other studies of high-gradient streams. Generally, lithology does not appear to influence step-pool size, spacing or depth of the pools. Channel gradient, width, and particle size seem to have a greater effect on step-pool morphology than does lithology. Channel width appears to be an additional important variable in influencing step wavelength and step-to-pool change in elevation for these streams.
We suggest that because lithology seems to have a minimal effect on step-pool spacing, energy dissipation and stream gradient are the fundamental physical attributes controlling step-pool spacing.