Consideration of land use in the evaluation of erosive processes in gully erosion

There are several factors that directly or indirectly influence erosion processes. In order to properly understand the behavior of these processes, some factors need to be analyzed together. Determining them wrongly can compromise the study resulting in wrong actions. For this reason, methodologies are always sought to measure them quantitatively and qualitatively in the most accurate possible way. Land use is one of the main factors liable to inaccuracies in its determination. To use this parameter in mapping erosive processes, researchers need to delimit it, classify it, and measure it. In order to better understand the complexity of considering this parameter, the present study analyzed an erosive feature that, although stabilized, has a component in constant development. Initially, a visual analysis indicated the same classification of land use for both conditions, despite having different behaviors, leading to the need for a detailed analysis. Such analysis comprised a historical survey through aerial photos and interviews with residents and employees of the city hall about the evolution of the feature from 2008 to 2019. It also included the analysis of other influencing factors that could be responsible for this difference in behavior in the area. Two different traces of the contribution areas of the gully and branch were also considered. One considering only aerial images, and the other considering the knowledge acquired during the research about the evolution of the feature. It was concluded, then, that an analysis of the use-only occupation factor based on aerial images can accentuate the inaccuracy of the measurement of this factor.

Assessment of a seismo-neotectonic origin for the New Liskeard–Thornloe scarp, Timiskaming graben, northeastern Ontario

To test an inference that the New Liskeard–Thornloe scarp (NLTS), Timiskaming graben, Ontario, is a deglacial–postglacial seismo-neotectonic fault, we collected shallow geophysical data along lines 7.2, 0.28, and 0.52 km long, located on three roads crossing the middle portion of the scarp. Data revealed a valley subsurface composed of bedrock (seismic unit a), glaciolacustrine–lacustrine deposits (units b to f), mass movement deposits (units ls 1 to ls 3), wave-worked sediments, mass wasting deposits and (or) artificial fill (unit g), and a minor occurrence of roadfill (unit h). The bedrock surface exhibits only minor undulations in the area underlying the scarp, indicating that the scarp morphology is unrelated to the underlying bedrock topography. Parallel reflectors in glaciolacustrine seismic units b and c conformably overlie the minor bedrock undulations and there is an absence of disturbed or offset zones within the reflectors underlying the scarp. This lack of disturbance or offset provides strong evidence that the scarp is not the product of deglacial–postglacial seismo-neotectonic faulting. The erosive truncation of glaciolacustrine seismic units d and e indicate that the scarp is an erosive feature cut into the glaciolacustrine deposits. It is likely a bluff formed by shoreline erosion, as is consistent with a geomorphic setting previously inundated by a large glacial lake and subsequent recessional lake stages. The non-fault origin for the NLTS limits the northern extent of the hypothesized Timiskaming East Shore Fault to within the Lake Timiskaming basin and, hence, constrains estimates of maximum rupture length.