Landslide development in a coastal valley in Northern Spain: conditioning factors and temporal occurrence

Sixty-five landslides have been mapped in the Meredal Valley, carved in one of the Asturian Precoastal Ranges on Mesozoic bedrock. From a genetic point of view, two groups of landslides can be distinguished: landslides developed mainly over Triassic lutites (complex movements, flows and rockslides) and landslides developed from calcareous cliffs (rock avalanches). Many of them are relict landslides, although evidence of activity can be recognized, as a result of a partial reactivation of some of the landslides. Four chronological classes have been established according to geomorphological criteria and the degree of preservation of the landslides. A lateral plugging deposit provides a minimum age of 5050±40 B.P. for the oldest class. In the same way, a stalactite gives to the third class of landslides a minimum age of 3392±128 B.P. The origin of landslides can be related to the plastic behavior of lutite and the permeability of the overlying limestone, which allows vertical seepage of water. From a regional point of view, landslides could be connected with Quaternary fluvial incision processes, as well as to Holocene high rainfall events.