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Deciphering the role of solar-induced thermal stresses in rock weathering

2016; Geological Society of America; Volume: 128; Issue: 9-10 Linguagem: Inglês

10.1130/b31422.1

1943-2674

Martha Cary Eppes, Brian I. Magi, B. Hallet, Eric Delmelle, Peter Mackenzie‐Helnwein, Kimberly Warren, S. Swami,

Seismic Waves and Analysis

Research Article| September 01, 2016 Deciphering the role of solar-induced thermal stresses in rock weathering Martha Cary Eppes; Martha Cary Eppes † 1Department of Geography and Earth Sciences, University of North Carolina at Charlotte, Charlotte, North Carolina 28223, USA †meppes@uncc.edu Search for other works by this author on: GSW Google Scholar Brian Magi; Brian Magi 1Department of Geography and Earth Sciences, University of North Carolina at Charlotte, Charlotte, North Carolina 28223, USA Search for other works by this author on: GSW Google Scholar Bernard Hallet; Bernard Hallet 2Department of Earth and Space Sciences, University of Washington, Seattle, Washington 98195, USA Search for other works by this author on: GSW Google Scholar Eric Delmelle; Eric Delmelle 1Department of Geography and Earth Sciences, University of North Carolina at Charlotte, Charlotte, North Carolina 28223, USA Search for other works by this author on: GSW Google Scholar Peter Mackenzie-Helnwein; Peter Mackenzie-Helnwein 3Department of Civil and Environmental Engineering, University of Washington, Seattle, Washington 98195, USA Search for other works by this author on: GSW Google Scholar Kimberly Warren; Kimberly Warren 4Department of Civil and Environmental Engineering, University of North Carolina at Charlotte, Charlotte, North Carolina 28223, USA Search for other works by this author on: GSW Google Scholar Suraj Swami Suraj Swami 1Department of Geography and Earth Sciences, University of North Carolina at Charlotte, Charlotte, North Carolina 28223, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Martha Cary Eppes † 1Department of Geography and Earth Sciences, University of North Carolina at Charlotte, Charlotte, North Carolina 28223, USA Brian Magi 1Department of Geography and Earth Sciences, University of North Carolina at Charlotte, Charlotte, North Carolina 28223, USA Bernard Hallet 2Department of Earth and Space Sciences, University of Washington, Seattle, Washington 98195, USA Eric Delmelle 1Department of Geography and Earth Sciences, University of North Carolina at Charlotte, Charlotte, North Carolina 28223, USA Peter Mackenzie-Helnwein 3Department of Civil and Environmental Engineering, University of Washington, Seattle, Washington 98195, USA Kimberly Warren 4Department of Civil and Environmental Engineering, University of North Carolina at Charlotte, Charlotte, North Carolina 28223, USA Suraj Swami 1Department of Geography and Earth Sciences, University of North Carolina at Charlotte, Charlotte, North Carolina 28223, USA †meppes@uncc.edu Publisher: Geological Society of America Received: 11 Sep 2015 Revision Received: 05 Feb 2016 Accepted: 01 Mar 2016 First Online: 02 Jun 2017 Online Issn: 1943-2674 Print Issn: 0016-7606 © 2016 Geological Society of America GSA Bulletin (2016) 128 (9-10): 1315–1338. https://doi.org/10.1130/B31422.1 Article history Received: 11 Sep 2015 Revision Received: 05 Feb 2016 Accepted: 01 Mar 2016 First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Martha Cary Eppes, Brian Magi, Bernard Hallet, Eric Delmelle, Peter Mackenzie-Helnwein, Kimberly Warren, Suraj Swami; Deciphering the role of solar-induced thermal stresses in rock weathering. GSA Bulletin 2016;; 128 (9-10): 1315–1338. doi: https://doi.org/10.1130/B31422.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract A dearth of direct field observations limits our understanding of individual mechanical weathering processes and how they interact. In particular, the specific contributions of solar-induced thermal stresses to mechanical weathering are poorly characterized. Here, we present an 11 mo data set of cracking, using acoustic emissions (AEs), combined with measurements of rock temperature, strain and other environmental conditions, all recorded continuously for a granite boulder resting on the ground in open sun. We also present stresses derived from a numerical model of the temperature and stress fields in the boulder, idealized as a uniform elastic sphere experiencing simple solar temperature forcing. The thermal model is validated using this study's data.Most observed cracking coincides with the timing of calculated maximum, insolation-driven, tensile thermal stresses. We also observe that most cracking occurs when storms, or other weather events, strongly perturb the rock surface temperature field at these times. We hypothesize that these weather-actuated thermal perturbations result in a complex thermal stress distribution that is superimposed on the background stresses arising from simple diurnal forcing; these additive stresses ultimately trigger measurable cracking. Measured locations of observed cracking and surface strain support this hypothesis in that they generally match model-predicted locations of maximum solar-induced tensile stresses. Also, recorded rock surface strain scales with diurnal temperature cycling and records progressive, cumulative extension (dilation), consistent with ongoing, thermal stress-driven subcritical crack growth in the boulder.Our results therefore suggest that (1) insolation-related thermal stresses by themselves are of sufficient magnitude to facilitate incremental subcritical crack growth that can subsequently be exploited by other chemical and physical processes and (2) simple insolation can impart an elevated tensile stress field that makes rock more susceptible to cracking triggered by added stress from other weathering mechanisms. Our observed cracking activity does not correlate simply with environmental conditions, including temperature extremes or the often-cited 2 °C/min thermal shock threshold. We propose that this lack of correlation is due to both the ever-varying ambient stress levels in any rock at Earth's surface, as well as to the fact that ongoing subcritical crack growth itself will influence a rock's stress field and strength. Because similar thermal cycling is universally experienced by subaerially exposed rock, this study elucidates specific mechanisms by which solar-induced thermal stresses may influence virtually all weathering processes. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.