Earth Science Frontiers ›› 2023, Vol. 30 ›› Issue (2): 506-513.DOI: 10.13745/j.esf.sf.2022.2.15

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Formation and transformation of condensate water inside rocks: Insight into source of rock moisture affecting weathering

OUYANG Kaigao1(), JIANG Xiaowei1,*(), MA Ce1, YAN Hongbin2, REN Jianguang2, FAN Yao2, ZHANG Runping2, FU Qianfang3, LI Xu3, WAN Li1   

  1. 1. School of Water Resources and Environment, China University of Geosciences(Beijing), Beijing 100083, China
    2. Yungang Research Institute, Datong 037034, China
    3. Beijing OUV Online Technology Co., LTD, Beijing 102218, China
  • Received:2021-09-10 Revised:2021-11-12 Online:2023-03-25 Published:2023-01-05
  • Contact: JIANG Xiaowei

Abstract:

Water plays an important role in controlling rock weathering, but there is still limited understanding of the source of rock moisture in rocks not directly exposed to sunshine and rainfall. In this study, a cave wall of the Yungang Grottoes in northern China is selected as an example for rock moisture measurement using the frequency domain reflection (FDR) method. Using the hourly monitoring data on the apparent rock water content at the rockwall between May 2020 to May 2021, different mechanisms controlling rock moisture fluctuations in summer and winter are identified. From early June to early October, the change of atmospheric humidity is the direct controlling factor for the increase and decrease of the rock moisture at the rockwall. Specifically, when atmospheric humidity gradient points to the interior of the mountain, water vapor migrates into the porous rock and condenses into liquid water, which increases rock moisture; inversely, liquid water within the rock evaporates thus decreases rock moisture. From middle October to early June, although the rock is relatively dry, the apparent rock water content of the rockwall surface layer still increases significantly in mid-December via cryosuction-induced water migration. This indicates that there is weakly bound water in the rockwall which can migrate and promote chemical weathering. By identifying an important moisture source in stone heritages, this study deepens the understanding of the rock weathering mechanism, and provides a decision-making basis for the conservation of stone heritages.

Key words: rock weathering, humidity, rock moisture, condensate water, capillary condensation, the Yungang Grottoes

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