Understanding Earth’s eroding surface with 10Be

Portenga, Eric W.; Bierman, Paul R.

doi:10.1130/g111a.1

Cited by 486 publications

(532 citation statements)

References 53 publications

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“…S5), evidently because exposed bedrock weathers slower than bedrock covered by soil in the Sierra Nevada (19,48). Previous cosmogenic nuclide studies of other granitic landscapes (e.g., 47) have shown that this is common (Fig. 4).…”

Section: Implications For Landscape Evolutionmentioning

confidence: 90%

“…A global compilation of cosmogenic nuclide data (gray, after ref. 47) demonstrates that erosion from soil-mantled granitic terrain (Bottom; n = 416) is typically faster than it is from exposed granitic bedrock (Top; n = 250). This is consistent with cosmogenic nuclides in samples from the Sierra Nevada study region (black, with labeled averages ± SEM and number of samples); erosion is more than two times faster on average in soil-mantled terrain (Bottom) than it is in bare rock (Top).…”

Section: Methodsmentioning

confidence: 99%

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Bedrock composition regulates mountain ecosystems and landscape evolution

Hahm

Riebe

Lukens

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

202

205

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Earth's land surface teems with life. Although the distribution of ecosystems is largely explained by temperature and precipitation, vegetation can vary markedly with little variation in climate. Here we explore the role of bedrock in governing the distribution of forest cover across the Sierra Nevada Batholith, California. Our sites span a narrow range of elevations and thus a narrow range in climate. However, land cover varies from Giant Sequoia (Sequoiadendron giganteum), the largest trees on Earth, to vegetation-free swaths that are visible from space. Meanwhile, underlying bedrock spans nearly the entire compositional range of granitic bedrock in the western North American cordillera. We explored connections between lithology and vegetation using measurements of bedrock geochemistry and forest productivity. Tree-canopy cover, a proxy for forest productivity, varies by more than an order of magnitude across our sites, changing abruptly at mapped contacts between plutons and correlating with bedrock concentrations of major and minor elements, including the plant-essential nutrient phosphorus. Nutrient-poor areas that lack vegetation and soil are eroding more than two times slower on average than surrounding, more nutrientrich, soil-mantled bedrock. This suggests that bedrock geochemistry can influence landscape evolution through an intrinsic limitation on primary productivity. Our results are consistent with widespread bottom-up lithologic control on the distribution and diversity of vegetation in mountainous terrain.erosion rates | bedrock weathering | critical zone | forest distribution V egetation captures solar energy and sends it cascading through ecosystems, creating habitats for other organisms and fixing nutrients and carbon from the atmosphere. Vegetation also plays an important although still incompletely understood role in the breakdown and erosion of rock (1-3) and thus the evolution of Earth's topography (4). Understanding the factors that determine where vegetation thrives-and where it does not-is therefore fundamental to many disciplines, including ecology, geomorphology, geochemistry, and pedology. As a substrate for life, lithology can influence overlying vegetation, spurring endemism due to the presence of toxins (5, 6) and limiting productivity where rock-derived nutrients are scarce (7-9). However, lithologic effects on vegetation are generally considered secondary to climatic factors such as the length of the growing season and the amount of moisture available for plant growth (10). Here we show that bedrock composition can drive differences in vegetation on par with the systematic altitudinal differences found in mountains between their hot, dry foothills and cold, wet alpine summits.

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Section: Implications For Landscape Evolutionmentioning

confidence: 90%

Section: Methodsmentioning

confidence: 99%

Bedrock composition regulates mountain ecosystems and landscape evolution

Hahm

Riebe

Lukens

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

202

205

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“…For possible values of C o , (0.001-10 mm/y; ref. 35), Z b will be above the elevation of an adjacent channel for K=∅ between ∼10 −13 and 10 −8 m/s (Fig. S4).…”

Section: Model For a Bottom-up Limit To Bedrock Weatheringmentioning

confidence: 99%

A bottom-up control on fresh-bedrock topography under landscapes

Rempe

Dietrich

2014

Proc. Natl. Acad. Sci. U.S.A.

224

310

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The depth to unweathered bedrock beneath landscapes influences subsurface runoff paths, erosional processes, moisture availability to biota, and water flux to the atmosphere. Here we propose a quantitative model to predict the vertical extent of weathered rock underlying soil-mantled hillslopes. We hypothesize that once fresh bedrock, saturated with nearly stagnant fluid, is advected into the near surface through uplift and erosion, channel incision produces a lateral head gradient within the fresh bedrock inducing drainage toward the channel. Drainage of the fresh bedrock causes weathering through drying and permits the introduction of atmospheric and biotically controlled acids and oxidants such that the boundary between weathered and unweathered bedrock is set by the uppermost elevation of undrained fresh bedrock, Z b . The slow drainage of fresh bedrock exerts a "bottom up" control on the advance of the weathering front. The thickness of the weathered zone is calculated as the difference between the predicted topographic surface profile (driven by erosion) and the predicted groundwater profile (driven by drainage of fresh bedrock). For the steady-state, soil-mantled case, a coupled analytical solution arises in which both profiles are driven by channel incision. The model predicts a thickening of the weathered zone upslope and, consequently, a progressive upslope increase in the residence time of bedrock in the weathered zone. Two nondimensional numbers corresponding to the mean hillslope gradient and mean groundwater-table gradient emerge and their ratio defines the proportion of the hillslope relief that is unweathered. Field data from three field sites are consistent with model predictions.

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“…If these rock-surface-lowering values from the Esperanza Fire are assumed to represent a typical fire effect and are multiplied by 20 fires per 1000 yr (fire recurrence interval of 50 yr), then the rock erosion rate would range from 14 to 246 mm/k.yr. The high end of this range exceeds reported erosion rates based on 10 Be concentration in bedrock surfaces (e.g., Portenga et al 2011) and does not seem to be a reasonable sustainable rate for this landscape. Our next consideration is whether the Esperanza Fire might be considered a typical chaparral wildfire.…”

Section: Discussionmentioning

confidence: 39%

Granitic Boulder Erosion Caused by Chaparral Wildfire: Implications for Cosmogenic Radionuclide Dating of Bedrock Surfaces

Kendrick¹,

Partin

Graham

2016

The Journal of Geology

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A B S T R A C TRock surface erosion by wildfire is significant and widespread but has not been quantified in southern California or for chaparral ecosystems. Quantifying the surface erosion of bedrock outcrops and boulders is critical for determination of age using cosmogenic radionuclide techniques, as even modest surface erosion removes the accumulation of the cosmogenic radionuclides and causes significant underestimate of age. This study documents the effects on three large granitic boulders following the Esperanza Fire of 2006 in southern California. Spalled rock fragments were quantified by measuring the removed rock volume from each measured boulder. Between 7% and 55% of the total surface area of the boulders spalled in this single fire. The volume of spalled material, when normalized across the entire surface area, represents a mean surface lowering of 0.7-12.3 mm. Spalled material was thicker on the flanks of the boulders, and the height of the fire effects significantly exceeded the height of the vegetation prior to the wildfire. Surface erosion of boulders and bedrock outcrops as a result of wildfire spalling results in fresh surfaces that appear unaffected by chemical weathering. Such surfaces may be preferentially selected by researchers for cosmogenic surface dating because of their fresh appearance, leading to an underestimate of age.

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Understanding Earth’s eroding surface with 10Be

Cited by 486 publications

References 53 publications

Bedrock composition regulates mountain ecosystems and landscape evolution

Bedrock composition regulates mountain ecosystems and landscape evolution

A bottom-up control on fresh-bedrock topography under landscapes

Granitic Boulder Erosion Caused by Chaparral Wildfire: Implications for Cosmogenic Radionuclide Dating of Bedrock Surfaces

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