Abstract
Weathering of rocks can cause severe geohazards, such as rockfalls and collapses, posing threats to human safety. Understanding the mechanisms of rock weathering and developing geotechnologies that can autonomously regulate this process are therefore essential for sustainable society. Although weathering is largely governed by physical and chemical processes, endolithic microorganisms are increasingly recognized as significant contributors. This biologically driven process, known as microbial weathering, has been observed on rock outcrops and cave surfaces; however, few studies have investigated its role in caves, and none have directly linked it to cave stability. In this study, we examined microbial weathering in an artificial sandstone cave (Nybi sandstone) in Okinawa, Japan, focusing on surface flora, microstructure, and rock strength. The cave, excavated ~80 years ago, shows advanced weathering on both its ceiling and sidewalls, limiting accessibility. Field investigations revealed a progressive decrease in sidewall strength from the upper to lower sections, where 16S rRNA analysis identified abundant microbial communities, including cyanobacteria. The activation of these microorganisms promotes bio-alkalization on the sandstone surface, accelerating weathering. These results demonstrate that microbial activity plays a crucial role in the deterioration of sandstone caves and should be considered in the assessment of cave safety and long-term stability.
https://ror.org/02z1n9q24 
