Ablation Rates in Limestone Cave Walls or Monuments Linked to Bat Guano —From In Situ Measurements in the Azé Cave (Monts du Mâconnais, France) to Laboratory Modelling

Abstract

In caves and monuments, biocorrosion caused by bats occurs partly under accumulations of guano. Tests were carried out both at cave temperature and under hot conditions in the laboratory on 4 different limestones. A comparison of the results obtained using these two methods shows that the processes leading to the weathering of the limestones are the same, and that the hot laboratory tests accelerate them in a well-constrained way. The higher the porosity and capillarity of the limestone, the faster the weathering process. The presence of large calcite crystals also favors weathering. In caves, the ablation rates obtained (8 mm/ka) are sufficient to destroy engravings in a few decades. In monuments, ablation rates are even higher because of the temperature, and could theoretically reach 32 cm/ka in extreme conditions at 80˚C. The laboratory test developed here can be adapted to the temperature of each case study. It has already demonstrated the mechanisms that lead from weathering to the formation of a phosphate crust.