Geochemical Study of Soil Trapped in Rock Cracks and Role of Plants on Soil Stability at the Peripheral Slopes of Borobudur, Central Java

Borobudur Temple is one of the world’s Seven Wonders, and the Borobudur periphery must be preserved because the location serves as a buffer zone supporting tourism. However, areas with steep slopes are prone to landslides due to soil and slope instability. This study aimed to characterize the mineralogy of fresh andesite rocks (FAR) and weathered breccia rocks (WBR), as well as the physicochemical nutrient content in the soil trapped in rock cracks (SC) and soil overlying rock (SO), and to investigate the role of plants on soil and slope stability. Field surveys were conducted to collect samples of FAR, WBR, SC, and SO, which were analyzed in the laboratory. FAR were observed through optical petrography, while WBR and SC were examined with X-ray diffraction (XRD) and X-ray fluorescence (XRF). SC and SO were measured for their physical and chemical properties. The study’s results identified that FAR contained 69%–89% weatherable minerals, while WBR and SC contained 46.9%–98.4% and 51.3%–98.7%, respectively. The mineral analysis revealed that FAR and WBR provided a source of weatherable minerals to SC and SO. SC had better soil characteristics for plant growth with higher pH and base saturation than SO. Plant-root systems play a vital role in soil stabilization in hilly areas. Root–plants distribution in SC enhances soil and slope stability by mechanical root–soil–rock interlocking and reduces runoff by creating root channels to enhance water infiltration. Parallel cracks significantly contribute to planar landslide events in the study area by creating low-strength surfaces that trigger sliding, particularly when the soil is saturated with water during rainfall. In conclusion, natural vegetative-based landslide mitigation is seen as a practical, affordable, and eco-friendly solution. In the future, the findings of this study can be generalized to areas with comparable characteristics, such as soil trapped in breccia rock cracks.