The Colca Canyon (Central Andes, Southern Peru), about 100 km long and 1–3 km deep, forms a magnificent cross section of the Earth’s crust giving insight into mutual relations between lithostratigraphical units, and allowing relatively easy interpretation of the fascinating geological history written in the rocky beds and relief. Current activity of tectonic processes related to the subduction of the Nazca plate beneath the South American Plate exposed the geological heritage within study area. Well-developed tectonic structures present high scientific values. The volcanic landforms in the Valley of the Volcanoes and around the Colca Canyon include lava flows, scoria cones and small lava domes. They represent natural phenomena which gained recognition among tourists, scientists and local people. Studies performed by the Polish Scientific Expedition to Peru since 2003 recognized in area of Colca Canyon and Valley of the Volcanoes high geodiversity, potential for geoturism but also requirements for protectection. The idea of creating geopark gained recently the approval of regional and local authorities with support from the local National Geological Survey (INGEMMET). The Geopark Colca and Volcanoes of Andagua would strengthen the relatively poor system of the protected areas in the Arequipa department, increasing the touristic attractiveness and determine constraints for sustained regional development.

Dating of alluvia of large rivers based on subfossil tree trunks is discussed using examples from the Vistula Valley near Kraków and from literature referring to Central Europe. The method, which has been used hitherto for dating alluvia based exclusively on single trunks or single generations, has led usually to erroneous results because the majority of trunks in the alluvia were redeposited. Den drochronology is helpful in solving problems of dating alluvia, which should use only in situ trunks, i.e., trunks with bark, sapwood and branches. Equally suitable materials are stumps in growth position, which were cut down with an axe and which are preserved by an aggradating river. These stumps possess well-preserved root systems with roots of a lower order. Redeposition of trunks in alluvia is associated with lateral migration of a river channel. Channel migration leads to the washing out of subfossil trunks of different ages from older alluvia. These trunks, heavier than water, are redeposited at the level of channel lag. Simultaneously, waterside trees undermined by the river accumulate at the water level in the upper parts of point bar deposits. This results in one series of channel deposits with two layers of trunks ('a sequence of simulate aggradation'). In recent centuries, after deforestation of floodplains, this mechanism lead to the formation of a single level of black oaks at the level of channel lag. Nevertheless, the spatial pattern of redeposited trunks may be helpful in reconstruction of the direction of palaeochannel migration.