Supplemental Material: Late Miocene–Pliocene onset of fluvial incision of the Cauca River Canyon in the Northern Andes

Supplemental Text S1; Supplemental Tables S1–S2; Data Set S1.

Supplemental Material: Late Miocene–Pliocene onset of fluvial incision of the Cauca River Canyon in the Northern Andes

Supplemental Text S1; Supplemental Tables S1–S2; Data Set S1.

Applicability of Geomorphic Index for the Potential Slope Instability in the Three River Region, Eastern Tibetan Plateau

Geomorphic indices (e.g., the normalized channel steepness index (Ksn) and the stream length-gradient index (SL)) highlight changes in fluvial shapes and gradients. However, the application of these indices was seldom used to identify potential landslide zones. In this study, we used the Ksn and SL indices to detect the significant variations in the stream power along river reaches, which are anomalies associated with landslides, in the Zengqu River watershed, the upper reaches of the Jinsha River. Most of the landslide anomalies originate along the trunk and surrounding tributaries below the knickpoint of the mainstream. This suggests an erosional wave is migrating upstream throughout the drainage area. The fluvial incision may generate over-steepened hillslopes, which could fail in the future. In addition, the divide asymmetry index (DAI) predicts the direction of the divide as the headwaters migrate toward lower relief, higher elevation surfaces. Landslides are expected to occur as the unstable divide migrates. The proposed methodology can benefit the detection and characterization of potential landslide zones. It should improve hazard and risk analysis and the identification of drainage network areas associated with landslides.

Decadal sediment dynamics of a perturbed fluvial system: the case of the man-made Marecchia River canyon, Northern Apennines

<p>River canyons are transient geomorphic systems shaped by river incision into bedrock and coupled by instability of the adjacent valley walls. Investigating the evolution of river canyons is typically challenging due to the geologic time scales involved. In this context, the Marecchia River, which hosts in its intermediate portion a 6-km canyon, developed since the early 1950’s following intense gravel mining, may be instructive. Indeed, this setting offers the opportunity to: (i) document canyon development through highly erodible pelitic rocks; and (ii) evaluate relevant upstream and downstream effects on fluvial morphodynamics. To these ends, we subdivide the 50-km stretch of the Marecchia River main stem into 22 homogeneous reaches and evaluate decadal geomorphic changes through analysis of LiDAR-derived digital elevation models (i.e., 2009 and 2019) in conjunction with planimetric changes of active channel width delineated on orthophoto-mosaics (i.e., 2009, 2012, 2014, 2017, 2019). The estimation of patterns and rates of fluvial erosion into bedrock and its geomorphic effects are essential for understanding landscape evolution and for applying sustainable sediment management plans.</p><p>In terms of volumetric changes, the entire river stretch recorded a decadal degradation of 2,516,150 m<sup>3</sup> (57%) and 1,884,700 m<sup>3</sup> of aggradation (43%), with a corresponding net volume loss of -631,450 m<sup>3</sup>. Highest specific volumes of aggradation were observed in a homogeneous reach located in the lower part of the study segment (0.5 m<sup>3</sup>/m<sup>2</sup>), while highest values of degradation were observed in the upper reach of the canyon (-2.3 m<sup>3</sup>/m<sup>2</sup>). During the 2009-2019 period, knickpoint headward migration within the canyon has progressed for approximately 500 m, producing an average bedrock incision of about 10 m. As documented by area and volume changes, both rates of fluvial incision and canyon widening, as modulated by landslide activity and valley wall collapses, are highest in proximity of the main knickpoint and tend to decrease progressively downstream. By March 2019, when the second LiDAR survey was conducted, the main knickpoint had reached the foundations of a major check dam, which eventually collapsed two months later. Upstream of the canyon, channel reaches displayed narrowing dynamics with an alternation of degradation and aggradation processes. In terms of total volumetric changes, these reaches presented an indirect correlation with confinement, with the most confined reaches acting as sediment transfer zones. In contrast, the segment downstream of the canyon displayed widening dynamics (+ 11 m on average) together with an increase of aggradation processes. Due to the pelitic nature of the hosting bedrock, despite the high geomorphic change observed, most of the material supplied by the canyon walls gets transported in suspension, contributing very little to the estimated budget of the Marecchia River's distalmost reaches. In this way, we argue that most part of the aggradation observed in this segment was originated upstream, bypassing the canyon.</p>

The role of the Nahr Menashe in the Messinian Salinity Crisis: formation, dissolution and fluvial incision of the top evaporite unit in the NE Levant Basin, Eastern Mediterranean

<p>The Nahr Menashe Unit (NMU), which forms the uppermost part of the Messinian succession,  is one of the most cryptic and elusive sedimentary units present in the Levant basin (Eastern Mediterranean). We use a high-resolution 3D seismic dataset from offshore Lebanon to propose a new interpretation for its formation and evolution. The NMU varies laterally across the basin both in thickness and internal seismic characteristics. The variably coherent cyclic seismic packages affected by fracturing, faulting suggests that the NMU represent a reworked, layered evaporite succession interbedded with siliciclastics derived from both the Lebanon Highlands and the Latakia Ridge. Widespread semi-circular depressions, random linear imprints, passive surface collapsing and residual mound features within the NMU suggest that post depositional diagenetic and/or strong dissolution process often affected its evaporite-rich subunits. The well-known extended valley and tributary channel systems characterising the uppermost NMU shows mainly erosional rather than depositional features. Erosion started after deposition of NMU as a consequence of the maximum base level fall during the last phase of the Messinian Salinity Crisis (MSC). The channel and valley system were subsequently infilled by layered sediments here interpreted to represent post-MSC deep water marine reflooding. In conclusion, our analyses suggest the NMU can be interpreted as a mixed evaporite-siliciclastic system deposited in a shallow marine or marginal environment, which subsequently experienced fluvial erosion and later burial by transgressive/high-stand sediments.</p>

When Individual Geosites Matter Less—Challenges to Communicate Landscape Evolution of a Complex Morphostructure (Orlické–Bystrzyckie Mountains Block, Czechia/Poland, Central Europe)

This paper explores problems associated with explanation of geoheritage at the landscape scale and argues that focus on individual geosites that show rock outcrops or small-scale landforms may not be sufficient to tell the story. The area of Orlické–Bystrzyckie Mountains Block in Central Europe lacks spectacular landforms or large rock outcrops, and yet has a most interesting geological history that involved Mesozoic planation, Cretaceous marine transgression and the origin of sedimentary cover, Cenozoic differential uplift and the origin of tectonic topography, resultant fluvial incision and Quaternary periglaciation. Individual geosites documented in the area fail to show this complexity and give an incomplete picture. Therefore, viewpoint geosites, allowing for in situ interpretation of regional landscapes, have a role to play and they collectively illustrate the effects of the main stages of geological and geomorphological evolution. In addition, the potential of simple visualization technologies is investigated, as these 3D visualizations may enhance ground views, putting things into even broader perspective.