Weathering rates of historic sandstone structures in semiarid environments (Ebro basin, NE Spain)

Long-term weathering rates of sandstones were obtained for well-dated (from 400 to 1100 years BP) historic structures (wall sections of the Alberuela Castle) in a semiarid environment of the central Ebro basin (NE Spain) using an exclusive movable contour-plotting frame. This sandstone has a low durability controlled mainly by textural properties. Differences observed in weathering rates are clearly controlled by the age of building as well as the orientation of the studied sandstone wall sections. Weathering processes related to insolation control the asymmetric spatial pattern of weathering rates in surfaces exposed for since 1100 BP, which are higher in southeast facing sandstone wall sections (8.4 mm/100 years) than in southwestern (4.4 mm/100 years) and northern faces (3.9 mm/100 years). In addition, exponential increase in weathering rates with time (from 1.6–2.2 mm/100 years in surfaces exposed for since 800–400 BP to 8.4 mm/100 years in surfaces exposed for since 1100 BP) in southeastern faces may be probably related to environmental changes during the last millennium.