Mass soil movement on terraced landscapes of the Mediterranean mountain areas: a case study of the Iberian Range, Spain

Terraces represent one of the most common agricultural landscapes in Mediterranean mountainous regions. However, the demographic and socioeconomic changes occurring in the second half of the last century caused terraces abandonment, leading to the loss of maintenance work required by these agricultural structures, and promoting various erosion processes, in particular the collapse of stone walls and small slides in risers. This paper analyses these mass movements by quantifying their size and frequency and defining the variables involved in their triggering in the upper valleys of Leza, Jubera and Cidacos rivers (Camero Viejo, Iberian Range, Spain), where bench terraces occupied 13,274 hectares (63% of agricultural space). A total amount of 240 small slides were recorded in 53 terraces studied, which means an average of 4.5 slides per plot and 33.1 m3 of material mobilized per 100 m of wall. This study proves that the most decisive causes for slides to start are related to soil infiltration capacity, as well as to the way in which water runs down the hillside.