In mountain regions the exposure of alluvial fans to sediment-laden flows can be remarkable, the generated damages to infrastructure and property enormous and the potential death-toll significant. The knowledge and understanding of distributive processes can be relevant for improving the effectiveness of risk mitigation strategies. With the aim of deepening the knowledge of distributive processes (i.e., autogenic or allogenic or both), a set of 144 experiments of unsteady two-phase flows were analyzed. The allogenic forcings were total flow volume (3 levels), solid fraction (3 levels), water release mode (2 levels). For each forcing factor combination 8 repetitions were accomplished on an unchanneled alluvial fan according to the 'similarity by process' method. Localized avulsions (Av), symmetric bifurcations (bS) and asymmetric bifurcations (bA) were retraced. Additionally, backstepping aggradation and channel plug were distinguished qualitatively. We assessed the occurrences of the observed distributive processes and their spatial variability by determining their directed distributions (i.e., spatial deviation ellipses). Moreover, we performed a set of one-way Kruskal-Wallis ANOVAs and inferred significant rank differences between the compared data groups (i.e., distributive process occurrences associated to specific allogenic forcing conditions). Irrespectively of the imposed conditions, avulsions predominantly occur in the upper part of the alluvial fan. Symmetric bifurcations tend to align more with the fan's longitudinal axis, while asymmetric bifurcations, albeit rare, are more common on the lateral portions of the fan. Avulsions are more common with the half-opened water release mode, releasing a high total flow volume and sediment concentrations. Symmetric and asymmetric bifurcation are more common under a fully opened water release mode. Setting the half-opened water release mode, distributive processes occur more frequently with a predominance of avulsions. The extraordinary variability of the occurred distributive process and their spatial patterns considering the peculiar effect of the water release mode should be carefully considered in hazard and risk assessment.
This study investigates the uplifted marine terraces along the western and eastern coasts of the Laconic Peninsula in an attempt to reconstruct the region's Late Pleistocene tectonic and geomorphological history. Using high-resolution topography, GIS analysis and extensive field surveys, the research mapped and characterized sequences of marine terraces in three distinct sectors. The analysis identified a sequence of eight terraces in Sector A and six in Sector B on the western coast, with five lower-elevation terraces in Sector C on the eastern coast. The marked difference in terrace elevation and number between the adjacent Sectors A (higher) and B (lower) is attributed to differential uplift caused by the active Molai graben. By correlating the lowest terrace in Sector B (at 9-10 m a.s.l.) with the MIS 5a terrace in the adjacent Punta area based on a previous study, a long-term average uplift rate of 0.36 +/- 0.11 mm a-1 over the past 215 +/- 5.5 ka is established for Sector B. Assuming this constant rate, the research tentatively correlated the higher terraces in Sector B with successive Quaternary highstands: MIS 5c (Terrace B, 15-21 m a.s.l.), MIS 7a (Terrace D, 55-65 m a.s.l.), and MIS 7c (Terrace E, 80-90 m a.s.l.). These correlations are consistent with predicted elevations derived from global sea-level curves. The results confirm that the regional coastal uplift is driven by the overall proximity to the Hellenic Subduction Zone, while local variations are controlled by active normal faulting.
