Rates of subcritical cracking and long-term rock erosion

Journal Article · Tue Sep 25 00:00:00 EDT 2018 · Geology

DOI:https://doi.org/10.1130/G45256.1· OSTI ID:1477884

Eppes, M. C. ^[1]; Hancock, G. S. ^[2]; Chen, X. ^[3]; Arey, J. ^[1]; Dewers, T. ^[4]; Huettenmoser, J. ^[2]; Kiessling, S. ^[1]; Moser, F. ^[1]; Tannu, N. ^[1]; Weiserbs, B. ^[1]; Whitten, J. ^[2]

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1. Univ. of North Carolina, Charlotte, NC (United States). Dept. of Geography and Earth Sciences
2. College of William and Mary, Williamsburg, VA (United States). Dept. of Geology
3. Univ. of Texas, Austin, TX (United States). Bureau of Economic Geology
4. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

Bedrock fracture is a key element of rock erosion and subsequent surface processes. We test the hypothesis that rock's susceptibility to subcritical cracking, a specific type of fracturing, significantly drives and limits rock erosion. We measured ¹⁰Be-derived erosion rates, compressive strength, and crack characteristics on 20 outcrops of different rock units (quartzite, granite, and two metasandstones) in the northern Blue Ridge Mountains of Virginia (USA). We also measured the subcritical cracking index (n), Charles’s law velocity constant (A), and fracture toughness (K_IC) of samples from four of the same outcrops, representative of each rock type. Erosion rates range from 1.16 ± 0.67 to 32.3 ± 7.8 m/m.y. We find strong correlations—across the four rock units—between average erosion rates and the three subcritical cracking parameters (R² > 0.85, p < 0.05), but not compressive strength (R² = 0.6; p > 0.1). We also find a correlative relationship between n and outcrop fracture length (R² = 0.91; p < 0.05). The latter correlation is consistent with that of published model predictions, further indicating a mechanistic link between subcritical cracking and rock erosion. We infer that subcritical cracking parameters closely tie to erosion rates, because subcritical cracking is the dominant process of mechanical weathering, leading to positive feedbacks relating subcritical cracking rates, crack length, porosity, and water accessibility. Finally, these data are the first that directly test and support the hypothesis that subcritical cracking can set the pace of long-term rock erosion.

• Research Organization: Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Univ. of Texas, Austin, TX (United States); Univ. of North Carolina, Charlotte, NC (United States); College of William and Mary, Williamsburg, VA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES); USDOE National Nuclear Security Administration (NNSA); USDOE Office of Fossil Energy (FE); United States Geological Survey (USGS); Univ. of North Carolina, Charlotte (United States); College of William and Mary (United States)
• Grant/Contract Number: NA0003525; SC0006883; FE0023316
• OSTI ID: 1477884
• Report Number(s): SAND-2018-9306J; 667314
• Journal Information: Geology, Vol. 46, Issue 11; ISSN 0091-7613
• Publisher: Geological Society of America
• Country of Publication: United States
• Language: English

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58 GEOSCIENCES