Sea Cliff Retreat Mechanisms in Northeastern Brazil

The coast of the State of Rio Grande do Norte at the Northeast Region of Brazil is undergoing an accelerated
process of urbanization. The coast of Rio Grande do Norte State is formed by cliffs and extensive dune fields.
The cliffs are formed by steep slopes with heights up to 50 m and inclinations to the horizontal ranging from 20º
to 90º. During the last few decades, facilities for tourist activities have been built at the top of the cliffs and
nearby region, ignoring the risks of landslides. This paper presents and discusses the retreat mechanisms of sea
cliffs monitored along 16 km of the coastline of the City of Tibau do Sul, Brazil. The modes of failure of vertical
sea cliffs include fall, topple, and slide from the upper part of the slopes. Surficial erosion and slides have been
identified in slopes with inclination between 45º and 60º. The stability of the cliffs becomes more critical when
seawater reaches its base. Under this situation, an incision at the toe of the cliff is formed by wave action,
triggering the instability of the upper layers. The action of the sea occasionally results in instabilities of major