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INTRODUCTION UNLIKE LARGE COMMUNITY CENTRES that may have formal, well-funded archives, small communities often rely on the knowledge of Elders to preserve local history. Increasingly, Indigenous and local knowledge is [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2008.04.010 Byline: Chris H. Hugenholtz Keywords: Mars; Mars; surface; Earth; Geological processes Abstract: Recent gully deposits on Mars have been attributed to both wet and dry mass wasting processes. In this paper frosted granular flow (FGF) is presented as a new hypothesis for recent mass wasting activity in martian gullies. FGF is a rare type of granular flow observed on a talus slope in the Province of Quebec, Canada [Hetu, B., van Steijn, H., Vandelac, P., 1994. Geogr. Phys. Quat. 48, 3-22]. Frost reduces dynamic inter-particle friction, enabling flows to mobilize onto relatively low slope gradients (25-30[degrees]) compared to those involving dry granular flow of the same material (35-41[degrees]). Resulting erosional and depositional features include straight to sinuous channels, levees and digitate to branching arrangements of terminal deposits. Similar features are commonly found in association with geologically-young gully systems on Mars. Based on terrestrial observations of FGF processes the minimum criteria required for their occurrence on Mars include: (i) readily mobilized, unconsolidated sediment at the surface; (ii) an upper slope gradient at or near the angle of repose; (iii) frost accumulation at the surface; and (iv) triggering by rock fall. All four conditions appear to be met in many areas on present-day Mars though triggering mechanisms may vary. Compared to terrestrial FGFs, which are lubricated by thin liquid films at inter-particle contacts, those occurring on Mars are more likely lubricated by vaporization of CO.sub.2 and small amounts of H.sub.2O frost that becomes incorporated in the translating mass. Some recent mass wasting activity in martian gullies, therefore, could be interpreted as the product of FGF. Author Affiliation: Department of Geography, University of Lethbridge, 4401 University Drive W., Lethbridge, AB T1K 3M4, Canada Article History: Received 17 January 2008; Revised 8 April 2008

Abstract: Sand supply is a major controlling factor on parabolic dune form and stratigraphy in inland settings. In this study, aerial photographs, ground-penetrating radar (GPR), and stratigraphic analysis document the [...]

This note describes a rare observation of naturally occurring free-falling streams of sand-water mixtures that form vertical sandcastle-like structures with complex interdigitate patterns. These emergent structures and patterns develop on sand dunes during winter via successive stacking of sand-laden flows of snow meltwater. Individual lobes comprising the structures are emplaced via infiltration-induced deposition-a process known as "sieve deposition." Collectively, the processes and vertical structures documented here provide an expanded context for understanding the behavior and emergent patterns of gravity-driven wet granular slurries in natural, uncontrolled settings. [ABSTRACT FROM AUTHOR]

Steep rock slopes present key opportunities and challenges within Earth science applications. Due to partial or complete inaccessibility, high-precision surveys of these high-relief landscapes remain a challenge. Direct georeferencing (DG) of unoccupied aerial vehicles (UAVs) with advanced onboard GNSS receivers presents opportunities to generate high-resolution 3D datasets without ground-based access to the study area. However, recent research has revealed large vertical errors using DG that may prove problematic in near-vertical terrain. To address these concerns, we examined more than 75 photogrammetric UAV-datasets with various imaging angles (nadir, oblique, and combinations) and ground control scenarios, including DG, along a steep slope exposure. Results demonstrate that mean errors in DG scenarios are up to 0.12 m higher than datasets using integrated georeferencing with well-distributed GCPs. Inclusion of GCPs greatly reduced mean error values but had limited influence on precision (<0.01 m) for any given imaging strategy. Use of multiple image angles resulted in the highest precisions, regardless of georeferencing strategy. These findings have implications for applications requiring the highest precision and accuracy (e.g., geotechnical engineering, hazard mitigation and mapping, and geomorphic change detection), which should consider using ground control whenever possible. However, for applications less concerned with absolute accuracy, our results show that DG datasets provide strong internal consistency and relative accuracy that may be suitable for high precision measurements within a model, without use of ground control. [ABSTRACT FROM AUTHOR]