Debris flow and long-term denudation rates in a tropical passive margin escarpment in South America

Abstract

Mass wasting events are frequent processes that occur on the steep slopes of passive-margin escarpments located in humid tropical regions. Not much is known about their role in the morphodynamics and morphogenesis of these escarpments. This study measured long-term denudation processes using cosmogenic 10Be produced in situ and characterized the sedimentary deposits to understand the role that debris flows have played in the dynamics and evolution of the oceanic slope of a sector of Serra do Mar, Brazil, the steepest passive-margin escarpment in South America. The findings indicate that the catchments were subjected to episodic debris flows, albeit with an uneven temporal distribution, and that these infrequent mass wasting episodes account for most of the escarpment erosion in Serra do Mar. In conclusion, debris flows are among the main geomorphological processes responsible for most of the erosion in this passive-margin escarpment, and they played a significant role in its retreat.