Análisis e interpretación de los perfiles longitudinales en la red fluvial del sur y sureste de Mallorca

Abstract

The analysis of river longitudinal profiles through the channel topography, derived from digital elevation model, is particularly useful for the extraction of geomorphological indicators. Surface topography reflects the competition and interaction between climatic and tectonic forces and. the shape of the longitudinal river profile contains this information. The modern landscape, defined by its climatic, geological history and current tectonic forces, has a state, transient or steady, that can be described through these indicators. In this work we have analysed 74 longitudinal profiles of 60 drainage basins located in the south and southeast of Mallorca, an area with semi-arid climatic conditions, low rates on tectonic activity and limited Quaternary dating. Through geomorphological indicators such as concavity and convexity, the results show that there are areas in clear state of immaturity and imbalance with a convex river profile and others with a concave profile on a dynamic equilibrium. There are 6 zones with particular characteristics affected by the local topography caused by crustal tilting and Neogene tectonic structures that disrupt that balance. The different carbonate lithologies, with its contrasting response to erosion and dissolution processes, display breakpoints on the concave-upward stream profiles, called knickpoints. In 31 of the 37 streams, lithological knickpoints have been found where the river flows through the contact between materials of the Pliocene and the Quaternary, and the Tortonian and the Messinian calcarenites. Moreover, for the physiographic context of the study area, a threshold has been found in the minimum drainage area, between 2.3 × 105 and 7.2 × 105 m2, from which a knickpoint is generated due to flow concentration. A knickpoint in the longitudinal profiles is a factor that generates a transient state in the evolution of the drainage network. In addition, reconstruction of paleoprofiles from knickpoints is useful for determining eustatic level changes or fault displacement under certain conditions. A 30 m displacement has been identified on a stream of the southern area which may indicate an uncharted dip slip fault block displacement.