THE INFLUENCE OF TRAVERTINE DAM STRUCTURES ON VALLEY MORPHOLOGY AT FOSSIL CREEK, ARIZONA

Travertine deposits in Fossil Creek in central Arizona create small-scale dams that produce a step-pool morphology along the stream. Travertine is formed by the precipitation of dissolved calcium carbonate out of saturated spring-derived stream water. In addition to actively growing travertine dams, relict structures can be found along the banks of the channel and on adjacent terrace surfaces. Although these relict dam structures have little to no influence on the present flow, their presence is a clear indication of past channel morphology, and may offer clues as to the long-term evolution of the valley. Basalt and sandstone bedrock frequently outcrops in the channel bed, suggesting that large floods are capable of breaching travertine dams and scouring into bedrock. Travertine may simply slow the process of bedrock incision and valley deepening, or conversely, it may actively contribute, by focusing energy dissipation in plunge pools at the base of large travertine structures. Bedrock steps are spatially correlated with both active and relict travertine structures, suggesting a feedback between the dynamics of travertine growth, bedrock incision and possibly knickpoint migration. Travertine may also play a role in valley widening, by trapping sediment in pools and directing flow against the valley walls. I will discuss the relationship of travertine dam structures to the step-pool morphology found along Fossil Creek, and explore the role they may play in the long-term incision of Fossil Creek into the Mogollon Rim. The project combines field mapping in combination with GPS survey data to correlate modern dam structures and step pool morphology with relict travertine structures.