Aspect-dependent variations in regolith creep revealed by meteoric 10Be

Abstract

Although variations in insolation and emergent feedbacks among soil moisture, vegetation, and soil cohesion are commonly invoked to explain topographic asymmetry that depends on aspect, few studies have directly quantifi ed the effi ciency of regolith transport along hillslopes of opposing aspect. We utilize meteoric 10 Be concentrations in regolith (n = 74) to determine mass fl ux along equatorial-facing and polar-facing hillslopes in three forested upland watersheds in and adjacent to the Susquehanna Shale Hills Critical Zone Observatory in central Pennsylvania (USA). In combination with regolith depth measurements and high-resolution topography, these fl uxes allow us to evaluate transport rate laws and the effi ciency of regolith creep. Concentrations of meteoric 10 Be in regolith along six separate transects imply that regolith fl ux is similar along all hillslopes, despite differences in topographic gradient and regolith thickness. Comparison of fl ux with regolith depth and topographic gradient reveals that transport depends on regolith depth, and that regolith creep is twice as effi cient along low-gradient, south-facing slopes with thin regolith as compared to steep, north-facing slopes mantled with thicker regolith. We suggest that the observed topographic asymmetry in these watersheds has evolved over geologic time as a result of differences in the frequency of freezethaw events between hillslopes of opposing aspect.

Designing a network of critical zone observatories to explore the living skin of the terrestrial Earth

“…Now, geophysicists travel among CZOs to image the subsurface with a battery of instruments to image the belowground landscape (St. Clair et al, 2015). In another example, after the Boulder Creek CZO began emphasizing slope aspect as a useful natural experiment to examine controls on CZ architecture and function in 2009, similar analyses at other CZOs led to highlighted linkages among aspect, water, biota, regolith structure, and episodic events (West et al, 2014;Ebel et al, 2015;Pelletier et al, 2017). Finally, a deep drilling project ("drill the ridge") was proposed and then pursued at many CZOs, and these data in turn led to a special issue describing regolith formation (Riebe et al, 2016).…”

Laser vision: lidar as a transformative tool to advance critical zone science

“…Generally, lidar information complements rather than replaces field observations, with lidar observations leading to new hypotheses and process cognition (Roering et al, 2013). Broadly, lidar technology has been useful in studying geomorphic response to extreme events such as fire and storms (e.g., Pelletier and Orem, 2014;Sankey et al, 2013;Perignon et al, 2013;Staley et al, 2014), human activities (e.g., James et al, 2009), and past climatic and tectonic forcings (e.g., Roering, 2008;Belmont et al, 2011;West et al, 2014). Meter-and sub-meter-scale time-varying processes, often derived from TLS, have been quantified in the response of point bar and bank morphodynamics (Lotsari et al, 2014) and in the formation of micro-topography due to feedbacks with biota (e.g., Roering et al, 2010;Harman et al, 2014).…”

“…Meter-and sub-meter-scale time-varying processes, often derived from TLS, have been quantified in the response of point bar and bank morphodynamics (Lotsari et al, 2014) and in the formation of micro-topography due to feedbacks with biota (e.g., Roering et al, 2010;Harman et al, 2014). Examples of larger scale change detection applications, typically ALS-derived, include measuring changes in stream channel pathways resulting from Holocene climate change and anthropogenic activities (e.g., Day et al, 2013;Kessler et al, 2012;James et al, 2012;Belmont et al, 2011), rates of change in migrating sand dunes (Pelletier, 2013), the influence of lithology and climate on hillslope form (e.g., Marshall and Roering, 2014;Hurst et al, 2013;Perron et al, 2008;West et al, 2014), and channel head formation (e.g., Pelletier et al, 2013;Pelletier and Perron, 2012;Perron and Hamon, 2012). Automated tools to identify geomorphic features (e.g., floodplains, terraces, landslides) and transitional zones (e.g., hillslope-to-valley, floodplain-tochannel) have been used in conjunction with high-resolution elevation data sets from lidar, including Geonet 2.0 (Passalacqua et al, 2010), ALMTools (Booth et al, 2009), and TerrEX (Stout and Belmont, 2014).…”

“…Physical and chemical properties of soil and rock, and vegetation structure are among the in situ observations commonly integrated with lidar data sets. For example, lidarbased studies have integrated distributed measurements of soil hydraulic properties (Harman et al, 2014) and soil thickness (Roering et al, 2010;Pelletier et al, 2014;West et al, 2014), as well as radioactive isotopes in soils (West et al, 2014). Lidar data sets have also been used to extend in situ observations of snow depth (Harpold et al, 2014a;Varhola and Coops, 2013) and carbon fluxes (Hudak et al, 2012) in both space and time.…”

Exploring the sensitivity on a soil area-slope-grading relationship to changes in process parameters using a pedogenesis model

“…Soil creep is the process of downslope movement of soil over a low grade slope with a substantial soil mantle under the force of gravity and friction (Ollier and Pain, 1996). Although soil creep can have a significant influence on some soil properties on some landforms (Braun et al, 2001;Roering et al, 2007;West et al, 2014) on landforms with interlocking rock fragments, its influence is not significant. On the other hand erosion can occur in all…”