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A field-based study of soils and the factors that influence their development is a strong, broad introduction to geologic concepts and research. A course blueprint is detailed where students design and complete a semester-long field-based soil geomorphology project. Students are first taught basic soil concepts and to describe soil, sediment and rock properties using standard description procedures. Then, with minimal geological or field experience, they are led to design and execute a project that examines how soil properties differ as a function of processes, parent material and time. By designing and executing the semester-long project, students gain familiarity with the entire geologic research process including basic field observation, hypothesis development and testing, interpretation and presentation skills. During the course, students learn 1) the basic knowledge necessary to describe geologic materials (soil, rock, sediment) in the field, 2) to make observations and interpret them in the context of geologic hypotheses which they have developed, 3) to develop, and execute a field-based research project, 4) to integrate and draw conclusions about complicated semi-quantitative data sets, 5) to map and survey in the field and 6) to present their research in a public forum. By the end of the semester students are able to make and test hypotheses relating soil properties to the depositional environment, age and/or type of geologic deposits in which they form. The knowledge, skills and research experience gained in this simple, semester-long project serve students well in upper-level courses and beyond. An example project is presented from a 2nd order stream and its adjacent tributary alluvial fans in the Piedmont of North Carolina.

Rock fractures are a key contributor to a broad array of Earth surface processes due to their direct control on rock strength as well as rock porosity and permeability. However, to date, there has been no standardization for the quantification of rock fractures in surface process research. In this work, the case is made for standardization within fracture-focused research, and prior work is reviewed to identify various key datasets and methodologies. Then, a suite of standardized methods is presented as a starting "baseline" for fracture-based research in surface process studies. These methods have been shown in pre-existing work from structural geology, geotechnical engineering, and surface process disciplines to comprise best practices for the characterization of fractures in clasts and outcrops. This practical, accessible, and detailed guide can be readily employed across all fracture-focused weathering and geomorphology applications. The wide adoption of a baseline of data collected using the same methods will enable comparison and compilation of datasets among studies globally and will ultimately lead to a better understanding of the links and feedbacks between rock fracture and landscape evolution. [ABSTRACT FROM AUTHOR]

Rock fracturing sets the pace for a range of geomorphic processes. While experimental studies and modeling have provided invaluable insights into the mechanisms and rates of rock fracturing as a function of stress, time, and environmental conditions, fieldbased observations of subaerial fracturing evolution over geologic time are scarce. To address this knowledge gap, we conducted a systematic study of fractures that developed subaerially and in situ within clasts perched on abandoned late Quaternary alluvial surfaces (ca. 0, ca. 14, and ca. 62 ka in age) in the hyperarid Dead Sea Rift Valley, Israel. Using quantitative field observations, petrographic, and scanning electron microscopy, and micron-scale laser scans of fracture surfaces we found that fractures exhibit a consistent pattern of three distinctive weathering zones: (1) an "Outer Zone," where fracture surface morphology resembles the clast exterior; (2) an "Accumulation Zone," where fractures are infilled by "loose" accumulated particles; and (3) an "Inner Zone" where fractures extend inward to the crack-tip and preferentially follow grain boundaries. Crack-tips are characterized as a distinct micro domain that consists of fracture-parallel microcracks, chemical alteration, and dissolution morphologies. Altogether, the laboratory results indicate chemically enhanced fracturing and infiltration of water ahead of traction-free, open crack-tips. Field measurements also revealed an increase in fracture number density over geologic time. Our results highlight new details regarding the progressive nature of mechanical weathering through geologic time and the role of moisture as a potential rate-setting factor in the fracturing that allows mechanical weathering. [ABSTRACT FROM AUTHOR]

Mechanical weathering both drives and limits a multitude of Earth processes ranging from carbon sequestration to formation of the soils and sediment that host life. Ample attention has been focused on individual stresses that may set the pace for mechanical weathering, but little effort has been made to identify the mechanisms by which the mechanical properties of rock modulate the impact of those stresses over timespans longer than those of human observation. Here we begin to test the newly proposed hypothesis that all mechanical weathering proceeds by subcritical cracking, whose rates are predicated on climate - separate from the influence that climate has on stress-loading. To first test the role of subcritical cracking parameters on long-term weathering and erosion, we measured 10Be-derived erosion rates of 20 outcrops comprised of four rock types in the Blue Ridge Mountains, VA USA. These rates ranged from ~1 to ~30 m/my. The chosen outcrops were interpreted to have had similar stress-loading histories. We also measured subcrticial cracking parameters of samples from four of the same outcrops. Bivariate correlations between averages of the erosion rates with those of the measured Subcritical Cracking Index (exponent n of Charles' Law), Charles' law constant A, and fracture toughness of the four rocks are strong (R2>0.85; P-value <0.05 for all). We found no statistical correlation between erosion rate and the critical rock parameter, compressive strength, measured on the outcrops with a Schmidt hammer. Then, to test the role of climate on subcritical cracking, we examine a three year record of subcritical cracking rate as measured by acoustic emission energy (AE) on a natural boulder set in full sun in the desert environment of New Mexico, USA. A full suite of per-minute meteorological data accompanied the cracking data. We find no statistical correlation between AE and commonly hypothesized stress-loading environmental variables – like diurnal temperature range. We attribute this finding to the non-linear nature of subcritical cracking acceleration as cracks increase in length, even as stresses remain relatively stable. We find a correlation between vapor pressure and subcritical cracking rate. Vapor pressure is known to strongly influence the rates of crack-tip, chemo-physical processes that constitute subcritical cracking. These datasets, together, begin to build a compelling case that mechanical weathering proceeds by climate-driven subcritical cracking. This conclusion encompasses broad implications for the interpretation of climate- and weathering-related datasets across the spectrum of Earth sciences. [ABSTRACT FROM AUTHOR]

Earth scientists are increasingly employing time series data with multiple dimensions and high temporal resolution to study the impacts of climate and environmental changes on Earth's atmosphere, biosphere, hydrosphere, and lithosphere. However, the large number of variables and varying time scales of antecedent conditions contributing to natural phenomena hinder scientists from completing more than the most basic analyses. In this paper, we present EVis (Environmental Visualization), a new visual analytics prototype to help scientists analyze and explore recurring environmental events (e.g. rock fracture, landslides, heat waves, floods) and their relationships with high dimensional time series of continuous numeric environmental variables, such as ambient temperature and precipitation. EVis provides coordinated scatterplots, heatmaps, histograms, and RadViz for foundational analyses. These features allow users to interactively examine relationships between events and one, two, three, or more environmental variables. EVis also provides a novel visual analytics approach to allowing users to discover temporally lagging relationships related to antecedent conditions between events and multiple variables, a critical task in Earth sciences. In particular, this latter approach projects multivariate time series onto trajectories in a 2D space using RadViz, and clusters the trajectories for temporal pattern discovery. Our case studies with rock cracking data and interviews with domain experts from a range of sub-disciplines within Earth sciences illustrate the extensive applicability and usefulness of EVis.