Weathering and Erosion of Rock Carvings in Sweden during the Period 1994-2003 Micro Mapping with Laser Scanner for Assessment of Breakdown Rates

This research report describes a 10-year long monitoring project for assessments of recent downwearing rates on rock carvings in southern and central Sweden. The investigations have been made by repeated measurements on the same sites with a laser scanner, especially constructed for the purpose. The scanner records the microtopography of rock surfaces with a resolution of 0.025 mm. From the field data accurate micro maps of areas up to 40x40 cm can be made. Deterioration rates are calculated by computerised comparisons of micro maps from consecutive measurements. A total number of 26 sites have been followed from 1994 to 2003. There are large variations in downwearing rates between the investigated places. Averages are, however, similar to those that can be expected from crystalline rocks in general in Scandinavia. It has also been revealed that the micro weathering is episodic. This means that periods with fast breakdown alternate with periods when almost nothing happens. Furthermore the spatial variation within the laser scanned areas of where downwearing takes place could be studied. Usually deterioration at times only takes place on limited spots while most of the micro mapped area is left unaffected. After material losses have taken place from these spots weathering continues at other places.