Terras caídas: Fluvial erosion or distinct phenomenon in the Amazon?

Abstract

In the Amazon River Basin, as in other hydrographic regions of Brazil and the world, fluvial erosion processes occur because of rivers dynamics. However, the lateral erosion that occurs on banks of Amazonian rivers, called terras caidas, typically is associated with gravitational movements and is mainly related to large landslides that can damage structures or kill people who live along these riverbanks. To better understand the erosive processes that occur in rivers of northern Brazil, especially those located in the Amazon River Basin, this work aims to describe the terras caidas phenomenon and determine whether it is a distinct phenomenon of fluvial erosion processes. The investigation includes analysis of hydrometeorological data of the National Water Agency (ANA), information collected during field expeditions, and mapping of geological and hydrological risk areas in the states of Amazonas, Acre, Rondonia, Para, and Amapa performed by the Geological Survey of Brazil—(CPRM) from 2011 to 2016. It is concluded that terras caidas is a distinct phenomenon in the Amazon rivers that is different from erosive processes in other Brazilian rivers, because it is associated not only with the lateral erosion, but also with mass movements of moderate and large extents, which cause landslips, undermining, creeps, and major landslides.