Hillslope evolution in response to lateral base level migration

Abstract

Hillslopes evolve in response to base level change, sediment production, and sediment transport. Many previous studies have focused on hillslopes undergoing vertical base level migration due to tectonic forcing and bedrock incision. Many geomorphic features, however, are characterized by lateral hillslope retreat and have not been adequately studied. Here I adapt a theory of linear diffusive hillslope evolution to relate the velocity of lateral hillslope retreat to the steady-state hillslope form. A case study in a Florida sapping network, in which headward migration of seepage faces in a sandy soil sets the base level for the surrounding hillslopes, provides numerous opportunities to test the analytical model by direct measurement. Measurements of hillslopes in the Florida sapping network found quantitative agreement between the predicted and observed hillslope morphology. An expected relationship between geometric drainage area and channel growth velocity was not borne out in the data, but the distribution of measured v/K ratios is consistent with what I expect based on my preferential sampling of slow-moving gently-sloped heads. Several explanations are given to explain why the expected relationship with drainage area is not observed, and suggestions for future work based on these findings is offered.