Weathering of runestones in a millennian perspective

Publisher Summary Runic monuments are Scandinavian specialty and can be divided into three groups: ancient runestones, Viking runestones from 11 th century, and medieval runic monuments from 12 th century and later. The chapter discusses the chronological century-long studies of stone weathering to define the total deterioration. This chapter focuses on the Viking age monuments, because they are the numerous and consist of erected, standing stones. The monuments were altered by weathering of chemical, biological, and physical nature. Through the centuries, the chemical and biological weathering alters the surface by increasing the porosity after the dissolution of more easily weathered minerals such as calcite, biotite, and anorthitic plagioclase (calcium-rich feldspar). This facilitates material loss by physical processes such as freeze/thaw cycles and salt crystallization/dissolution. Thus, the weathering increases strongly with time. Different bedrock types show different weathering rates. Isotropic siliceous rocks such as granite are more resistant, while anisotropic rocks such as limestone and sandstone degrades more rapidly. This pattern is illustrated in the examination of 22 different runic monuments in Sweden. Many factors tend to disguise this general pattern, the most important being human interference.