The role of geological conditions in the disintegration of historical structures on the escarpment of the Lower Vistula Valley, on the example of Chełmno (Poland)

Abstract Chełmno is a town in the north-western part of the Chełmno Lakeland. It is one of few towns in Poland to have fully preserved its medieval defensive walls. Its touristic and natural environs make it a popular tourist destination. The town’s location near the escarpment of the Vistula valley mean that the preserved historical structures (including the defensive walls) are under threat. A few years ago a buttress became detached and two sections of the defensive walls collapsed. One part was rebuilt (the site where the studies were conducted), while the second part remains unrestored. Bricks are also progressively coming away. This situation may be the result of several factors, although the authors claim that the most important are the geological structure and the wall foundations (which are shallow, at a depth of 1-2 m, with the wall having been built up higher in the 16th century).