Shakedown in Madagascar: Occurrence of lavakas (erosional gullies) associated with seismic activity

Erosion via lavaka formation is widespread in Madagascar, but controls on why and where lavakas occur are not understood. Geographic information system analysis reveals a spatial correlation between lavaka abundance and the frequency of seismic events: most lavakas occur in or near areas where recorded earthquakes (magnitude 0.5-5.6) are most frequent. This correlation explains the unevenness of lavaka distribution in the Malagasy highlands, and highlights the importance of natural factors in lavaka formation. Seismic activity appears to precondition the landscape to lavaka formation, although the mechanism by which this happens is not yet known. Recognizing the connection, however, allows us to pinpoint areas prone to future lavaka development in zones of active deforestation. Areas with the greatest frequency of seismic events are most at risk for high-density lavaka development.