10. How Porosity Increases During Incipient Weathering of Crystalline Silicate Rocks

Navarre‐Sitchler, Alexis; Brantley, Susan L.; Rother, Gernot

doi:10.1515/9781501502071-010

Cited by 8 publications

(5 citation statements)

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“…As mineral assemblages in exhumed rocks re-equilibrate with meteoric fluids over many regions of the Earth's surface, the density of pores and fractures in bedrock often increases (Molnar et al, 2007;Navarre-Sitchler et al, 2015;St Clair et al, 2015) until the bedrock disaggregates and begins to form soil. Such disaggregation eventually allows physical removal of the soil and rock material by mechanical transport or chemical removal as solutes in flowing fluids.…”

Section: Introductionmentioning

confidence: 99%

Exploring an ‘ideal hill': how lithology and transport mechanisms affect the possibility of a steady state during weathering and erosion

Lebedeva

Brantley

2020

Earth Surf Processes Landf

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We present a model of chemical reaction within hills to explore how evolving porosity (and by inference, permeability) affects flow pathways and weathering. The model consists of hydrologic and reactive‐transport equations that describe alteration of ferrous minerals and feldspar. These reactions were chosen because previous work emphasized that oxygen‐ and acid‐driven weathering affects porosity differently in felsic and mafic rocks. A parameter controlling the order of the fronts is presented. In the absence of erosion, the two reaction fronts move at different velocities and the relative depths depend on geochemical conditions and starting composition. In turn, the fronts and associated changes in porosity drastically affect both the vertical and lateral velocities of water flow. For these cases, estimates of weathering advance rates based on simple models that posit unidirectional constant‐velocity advection do not apply. In the model hills, weathering advance rates diminish with time as the Darcy velocities decrease with depth. The system can thus attain a dynamical steady state at any erosion rate where the regolith thickness is constant in time and velocities of both fronts become equal to one another and to the erosion rate. The slower the advection velocities in a system, the faster it attains a steady state. For example, a massive rock with relatively fast‐dissolving minerals such as diabase – where solute transport across the reaction front mainly occurs by diffusion – can reach a steady state more quickly than granitoid rocks in which advection contributes to solute transport. The attainment of a steady state is controlled by coupling between weathering and hydrologic processes that force water to flow horizontally above reaction fronts where permeability changes rapidly with depth and acts as a partial barrier to fluid flow. Published 2020. This article is a U.S. Government work and is in the public domain in the USA.

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Section: Introductionmentioning

confidence: 99%

Exploring an ‘ideal hill': how lithology and transport mechanisms affect the possibility of a steady state during weathering and erosion

Lebedeva

Brantley

2020

Earth Surf Processes Landf

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“…In natural systems, the depth of weathering has also been observed to increase with the density of fracturing (e.g., Dewandel et al, 2006). Conversely, both L and ℓ are very small for massive, unfractured rocks such as diabase (Bazilevskaya et al, 2013;Bazilevskaya et al, 2015;Navarre-Sitchler et al, 2015). Brantley et al (2017) also simulated weathering of a hill of fractured bedrock eroding at constant rate E under the steady-state condition that E = W. As in the models in Figure 2c,d, the hill geometry was parabolic and dictated by the value of E. The hills were allowed to evolve to a constant regolith thickness L (Figure 4c,d).…”

Section: Fractured Versus Unfractured Rocksmentioning

confidence: 99%

Section: Fractured Versus Unfractured Rocksmentioning

confidence: 99%

Relating land surface, water table, and weathering fronts with a conceptual valve model for headwater catchments

Brantley

Lebedeva

2020

Hydrological Processes

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Knowing little about how porosity and permeability are distributed at depth, we commonly develop models of groundwater by treating the subsurface as a homogeneous black box even though porosity and permeability vary with depth. One reason for this depth variation is that infiltrating meteoric water reacts with minerals to affect porosity in localized zones called reaction fronts. We are beginning to learn to map and model these fronts beneath headwater catchments and show how they are distributed. The subsurface landscapes defined by these fronts lie subparallel to the soil-air interface but with lower relief. They can be situated above, below, or at the water table. These subsurface landscapes of reaction are important because porosity developed from weathering can control subsurface water storage. In addition, porosity often changes at the weathering fronts, and when this affects permeability significantly, the front can act like a valve that reorients water flowing through the subsurface. We explore controls on the positions of reaction fronts under headwater landscapes by accounting for the timescales of erosion, chemical equilibration, and solute transport. One strong control on the landscape of subsurface reaction is the land surface geometry, which is in turn a function of the erosion rate. In addition, the reaction fronts, like the water table, are strongly affected by the lithology and water infiltration rate. We hypothesize that relationships among the land surface, reaction fronts, and the water table are controlled by feedbacks that can push landscapes towards an 'ideal hill'. In this steady state, reaction-front valves partition water volumes into shallow and deep flowpaths. These flows dissolve low-and high-solubility minerals, respectively, allowing their reaction fronts to advance at the erosion rate. This conceptualization could inform better models of subsurface porosity and permeability, replacing the black box.

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“…The vegetation succession and species change after disturbance will depend not only on local ecosystem resilience, but also on climate (Rother & Veblen, 2016, 2017) and on existing CZ structure (i.e., deep and porous soils vs. low subsurface storage) (Tague & Moritz, 2019). Over long periods of time, disturbance severity and return intervals can govern processes such as weathering fluxes, subsurface porosity development (Navarre‐Sitchler et al., 2009, 2013, 2015), and surface erosion (Orem & Pelletier, 2015, 2016). One commonality across disturbance vectors for montane forests is an expectation that climate change will increase the occurrence, severity, and extent of disturbance (Dale et al., 2001; Loehman et al., 2017; Tague et al., 2019).…”

Section: Introductionmentioning

confidence: 99%

Seeing the Disturbed Forest for the Trees: Remote Sensing Is Underutilized to Quantify Critical Zone Response to Unprecedented Disturbance

et al. 2023

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Understanding the severity and extent of near surface critical zone (CZ) disturbances and their ecosystem response is a pressing concern in the face of increasing human and natural disturbances. Predicting disturbance severity and recovery in a changing climate requires comprehensive understanding of ecosystem feedbacks among vegetation and the surrounding environment, including climate, hydrology, geomorphology, and biogeochemistry. Field surveys and satellite remote sensing have limited ability to effectively capture the spatial and temporal variability of disturbance and CZ properties. Technological advances in remote sensing using new sensors and new platforms have improved observations of changes in vegetation canopy structure and productivity; however, integrating measures of forest disturbance from various sensing platforms is complex. By connecting the potential for remote sensing technologies to observe different CZ disturbance vectors, we show that lower severity disturbance and slower vegetation recovery are more difficult to quantify. Case studies in montane forests from the western United States highlight new opportunities, including evaluating post‐disturbance forest recovery at multiple scales, shedding light on understory vegetation regrowth, detecting specific physiological responses, and refining ecohydrological modeling. Learning from regional CZ disturbance case studies, we propose future directions to synthesize fragmented findings with (a) new data analysis using new or existing sensors, (b) data fusion across multiple sensors and platforms, (c) increasing the value of ground‐based observations, (d) disturbance modeling, and (e) synthesis to improve understanding of disturbance.

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10. How Porosity Increases During Incipient Weathering of Crystalline Silicate Rocks

Cited by 8 publications

References 43 publications

Exploring an ‘ideal hill': how lithology and transport mechanisms affect the possibility of a steady state during weathering and erosion

Exploring an ‘ideal hill': how lithology and transport mechanisms affect the possibility of a steady state during weathering and erosion

Relating land surface, water table, and weathering fronts with a conceptual valve model for headwater catchments

Seeing the Disturbed Forest for the Trees: Remote Sensing Is Underutilized to Quantify Critical Zone Response to Unprecedented Disturbance

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