Relict Landscape Research Articles

Mio‐Pliocene paleo‐course of Indus River in Upper Sutlej‐Zhada basin: Implication of tectonic uplift on river piracy and drainage reorganization in SW Tibet and NW Himalaya

AbstractWe analysed the elevated low‐relief relict landscapes in the transient Upper Satluj‐Zhada basin and the adjoining region in the tectonically active north‐western (NW) Himalaya–south‐western (SW) Tibetan orogen to understand the evolution of the regional landscape and drainage system under the influence of the Karakoram Fault‐Leo‐Pargil Horst system. This elevated low relief landscape represents the Mio‐Pliocene establishment of a new river network, which testimonies the present Sutlej River, which has been experiencing a transient surface uplift‐incision regime since (~4–1 Ma) with a local base level at the confluence of the Sutlej and Spiti River. The Miocene exhumation of the Ayilari Range and Leo‐Pargil Horst across the Karakoram fault (KF) system led to headward erosion, which abandoned the Paleo‐Sutlej‐Indus drainage system, which in turn caused drainage reversal along Qusum detachment (QD) and produced southward migration of the Paleo‐Sutlej River towards the mountain front. Our results indicate that the Upper Indus River has significantly lower χ‐ranges at higher elevations as compared with the adjacent Upper Sutlej River at lower elevations, which corresponds with a river piracy model that incorporates area gain‐loss feedback. The Upper Sutlej River in the Zhada basin is characterized by a comparable series of coplanar slope‐break knickpoints at ~4000–4500 m elevation, and their adjoining divides are in a state of disequilibrium as a consequence of the very high rapid incision across the Leo Pargil Horst, which drives the regional gradation process. The headward‐eroding Upper Indus River captured the proto‐Sutlej due to a base‐level change of >~1500 m, which significantly impacted the regional growth pattern and tectonics. The Mio‐Pliocene sedimentation pattern of the Upper Sutlej‐Zhada basin in the SW Tibet–NW Himalaya reflects this regional drainage capture, tectonic uplift and paleo‐drainage reorganization. The present finding has wider implications for the Mio‐Pliocene reorganization of drainage systems and the possible linkage of the Upper Indus River with the Paleo‐Sutlej over the Zhada basin.

Geomorphic evolution of Sutlej valley catchment in Western Himalayas: Imprint of surface processes in modulating fluvial erosion

The Sutlej River catchment in the tectonically active western Himalayas has several geomorphic signatures of river piracy and drainage reorganization across the Upper Sutlej-Zhada basin upstream. The accelerated growth of the Leo-Pargil Horst across the Kaurik Chango-fault (KC-fault) Zone and affected regional tectonics triggered enormous incisions, causing southward migration of the present Sutlej River, which is highly infested by bedrock landslides and debris flows and evolves as a very steep valley catchment. In order to understand the changing regional landscape and identify the tectonic perturbation over the channels, we evaluate the slope-break knickpoints in the Sutlej River profile. Furthermore, we model the presence of an elevated low-relief relict landscape in the Upper Sutlej-Zhada basin and the rapid incising lower Sutlej valley catchment using the Celerity model. The observation suggests that major knickpoints at ~2000–3000 m elevation comprise the fluvial erosion process, while higher elevation knickpoints recommend the hillslope process. In order to understand how fluvial erosion and surface process imprints have changed the landscape over time, we spatially correlate terrestrial datasets, such as rates of denudation and exhumation ages, with topographic metrics and climate variables. We observe a strong correlation between the pattern of denudation rates and the conditioning factors that modulate the surface processes. Increased channel erosion, high stream power, topographic metrics, and the occurrence of bedrock landslides over a regional structural disruption exhibit a positive spatial relationship, but their role in regional drainage capture, tectonic uplift, and the gradation process remains poorly understood.

River profile and relict landscape analysis reveal the Cenozoic geomorphic evolution of the Nihewan Basin in North China

The Nihewan Basin, renowned for the numerous world-class Paleolithic sites and diverse mammalian fauna preserved in its sedimentary sequence, is a key area for studying early human evolution in East Asia. Despite extensive studies on the fluvial-lacustrine basin sediments, the evolution and formation process and mechanism of the Nihewan Basin and Nihewan Paleolake remain unclear. Here we assess the spatial pattern and recent history of rock uplift of the Liuleng Shan, one of the main bedrock mountain ranges encompassing the Nihewan Basin, using river profile and topographic analysis. The transient topography of the Liuleng Shan is characterized by two generations of elevated non-lithological slope-break knickpoints that delimit the uplifted Dianziliang and Tangxian relict landscape surfaces, suggesting two episodes of accelerated rock uplift during the Cenozoic. We link the first phase of rapid rock uplift to the initiation of the central and northeastern portions of the North Liuleng Shan Fault (NLSF) during the opening of the Shanxi Graben System in the Late Miocene, implying the initiation of the Nihewan Basin at this time. We propose that the dextral transtensional southwestern portion of the NLSF formed and propagated northeastward at around 4.2 Ma, and was responsible for the second phase of surface uplift. This phase of deformation also terminated the Tangxian planation process and led to the further subsidence of the Nihewan Basin. Accordingly, drainage rearrangement and fault activity hydrologically closed the Nihewan Basin, resulting in the development of the Nihewan Paleolake. Our findings outline a timeline for the geomorphic evolution of the Nihewan Basin and Nihewan Paleolake, highlighting the dominant role of tectonics in their formation.

Historical geography and local history

Historical geography and local history originated in two separate parent subjects, geography and history. This is reflected in het the approaches they adopt respectively. They share, however, a common field of investigation: the development of an area or region through time, which explains why in the last twenty-five years the differences between them have become blurred. Of all the definitions for historical geography probably only four are significant today: the geography behind history; the reconstruction of past landscapes; the evolution of the cultural landscape; and the study of relict features. As far as the prospects for historical geography in South Africa are concerned, broad outlines only have been drawn and there are ample fields for research, e.g. frontier studies, which relate to colonisation and settlement history, and the study of relict landscapes. A vast number of questions about the evolution and appearance of the landscape need to be answered, and both historical geography and local history seek these answers.

The Fischbach Alps: A Geomorphological Record of late Neogene Uplift at the Eastern Margin of the European Alps

Abstract Low-relief surfaces at high elevations are peculiar features of the Eastern Alps that are best explained as relicts of morphological base levels that escaped erosive decay during uplift. To expand our knowledge of such surfaces in the Eastern Alps, the Fischbach Alps at the eastern end of the range are investigated. There, a large number of these elevated low-relief surfaces have been known for some time, but modern mapping is absent and their genesis is not well understood. A combined approach of field mapping, morphometric analysis of a digital elevation model and downstream projection of geomorphic equilibrium sections in river profiles was employed to: (i) create a geomorphological map of the region and (ii) to extract quantitative data from river profiles to infer the amount of uplift and incision. Six discrete levels of low-relief surfaces and relict landscapes are recognized at elevations between ~500 m and ~1600 m. Some of the lower levels are interpreted to relate to the well-known Trahutten, Landscha and Stadelberg levels, known from other parts of Styria, respectively. Mapped low-relief surface levels follow the northward directed topographic gradient in the mountainous region of the Fischbach Alps. The formation of elevated low-relief surfaces is consistent with a Piedmonttreppen model, where successive phases of tectonic uplift and tectonic quiescence led to a succession of incised landscapes and low-relief surfaces. However, the entire region south of the Murztal was also then tilted towards the Styrian Basin by about ~1–2°. Swath profile analysis for the Raab and Weizbach Klamm suggests a minimum of ~400–450 m incision since the formation of the so called Hubenhalt level. This implies that the geomorphic response to tectonic uplift after the formation of the higher Wolscheneck and Koralm relict landscapes led to an estimated incision of up to 1000 m (868±101 m), relative to the base level of today’s Styrian Basin at ~380 m. By comparing published age data to the presented mapping results, the onset for much of the uplift at the eastern end of the Alps is suggested to lie between ~4–7 Ma, before the formation of the Hubenhalt and Trahutten levels. Because the mapped levels correlate well with those in many other regions at similar elevations, a growing body of work now suggests that the underlying uplift event has a large wavelength.

Transient response to changes in uplift rates in the northern Atlas-Meseta system (Morocco)

Transient topography represents an opportunity for extracting information on the combined effect of tectonics, mantle-driven processes, lithology and climate across different temporal and spatial scales. The geomorphic signature of transient conditions can be used to unravel landscape evolution, especially in areas devoid of stratigraphic constraints. The topography of the Western Moroccan Meseta domain (WMM) is characterized by elevated non-lithological knickpoints, that delimit an uplifted relict landscape, implying a transient response to a change in uplift rate that occurred during the Cenozoic. Here, we determine denudation rates of selected watersheds and bedrock outcrops from cosmogenic nuclides and perform stream profile, regional and basin-scale geomorphic analysis. Denudation rates of the relict and the rejuvenated landscape range from 15 to 20 m/Myr and from 30 to 40 m/Myr, respectively. Rock uplift rates from river-profile inversions are 10–25 m/Myr from 45 to 22 Ma and 30–55 m/Myr from 22 to 10 Ma. Despite the different time scales, the inverted rates are consistent with 10Be averaged denudation rates (15–20 and 30–40 m/Myr) and river incision values from Pleistocene lava flows (<10 and ~50 m/Myr) for the rejuvenated and relict regions of the WMM. These results agree with geological data and indicate that the observed ~400 m of surface uplift in the WMM started to develop possibly during the early Miocene (first phase). Given the wavelength of the topographic swell forming the topography of the WMM, uplift is here interpreted to reflect localized crustal thickening through magma addition or lithospheric thinning through mantle delamination. More recently, the occurrence of late Miocene marine sediments at ~1200 m of elevation indicates that the adjacent Folded Middle Atlas during the last 5–7 Ma experienced surface uplift at ~170–220 m/Myr. Considering the cumulative amount of surface uplift that varies eastward from 400 to 800 and 1200 m from the Meseta to the Tabular and the Folded Middle Atlas, as well as the spatio-temporal pattern of alkaline volcanism (middle Miocene and Pliocene to Present), we suggest that the most recent episode (second phase) of surface uplift was induced by a larger-scale process that most likely included upwelling of asthenospheric mantle and to a lesser extent crustal shortening in the Folded Middle Atlas.

Post-lacustrine evolution of a tectonically-controlled intermontane basin: Drainage network analysis of the Mercure basin, southern Italy

Topographic analysis, drainage network morphometry, river profile analysis, and spatial distribution of fluvio-lacustrine terraces have been used to reconstruct the drainage network evolution in the Mercure River basin, a large intermontane tectonic basin of the axial zone of southern Apennines. Morphotectonic evolution of the study area is mainly controlled by poly-kinematics high-angle WNW-ESE and NE-SW faults, which promoted the development of a complex landscape with relict landscapes and/or low-relief erosional surfaces that occurred in a staircase arrangement at the top of the landscapes or at higher altitudes than the basin infill. The creation of the accommodation space for the deposition of the thick basin infill was related to an important tectonic phase of block-faulting along N120°-trending normal faults, which occurred in the final part of the Lower Pleistocene. Such an evolution strongly controls the longitudinal profile forms of channels draining the northern sector of the study area, which are featured by a well-developed concave-up segment in river profiles of these channels between an upward trait with lower values of channel steepness and the trace of the master fault. River profiles in north-western and south-east sectors of the Mercure River basin exhibit clear knickpoints at altitudes comparable with those of the superimposed orders of relict landscapes related to the initial formation of the tectonic basin and the subsequent evolution of the endorheic basin, with a post-lacustrine geomorphological evolution of the drainage network that is controlled by fluvial incision occurring at rates comparable than those reconstructed by independent morphotectonic markers. The erosion of the threshold of the endorheic basin occurring during the base-level fall of the MIS 12 promoted a dramatic base-level fall of about 150 m, which corresponds to a mean incision rate of about 0.35 mm/yr. Post-lacustrine evolution of the Mercure basin strongly controls the morphometric features of the drainage network, which preserves a centripetal pattern with several planimetric anomalies such as counterflow and high-angle confluences, local-scale fluvial capture phenomena and drainage divide migrations.

Prehistoric settlements and rivers in the Lithuanian coastal area in the Early Holocene

The search for sites inhabited by humans of the Late Palaeolithic to Mesolithic period on the coasts of Lithuania is closely related to the coastal and underwater relicts of the Early Holocene and palaeo-watercourses. This article presents the results of coastal, underwater and seismic seabed surveys. The estuaries of the rivers of the Late Mesolithic period could have been at the present seabed level at a depth of 30 m or even deeper. The watercourse sites of the Littorina Sea stage are in shallow coastal waters. At the latitude of Šventoji, Palanga, Klaipėda, Juodkrantė and the area of the Nemunas palaeo-estuary, the seabed was explored with side-scan sonar and by diving. An artefact from the Early Neolithic period has been found in the coastal area next to Klaipėda, and underwater, at a depth of 14.5 m, a relict tree stump has been detected. Two sites at a depth of 10–12 m can be associated with the relict Danė watercourse containing the preserved fragments of relict landscapes. During marine seismic survey, the probable Smeltalė River palaeo-watercourse was detected, and three sites of the former watercourses found to the south of Klaipėda could be the traces of the Dreverna palaeo-river estuary. This area has good prospects as regards the search for Early Mesolithic period settlements. The underwater survey showed no traces of human activity. A further search for the Stone Age sites would be more promising in locations where palaeo-landscapes have survived adjacent to the palaeo-watercourses.

Reconstruction of the Meso-Cenozoic tectono-geomorphological evolution of the Keguqin mountain in the Central Tian Shan based on geomorphological analysis and low-temperature thermochronology

Forming the northwestern branch of the Chinese Tian Shan, the Keguqin mountain located north of the Yili basin is characterized by Mesozoic relict landscapes and active faults, which recorded abundant information of long term tectono-geomorphologic evolution of the Tian Shan mountain range. However, the post-Jurassic deformation history of the Keguqin mountain is unclear. In this study, we applied apatite fission track, apatite (UTh)/He and geomorphologic analyses to reconstruct the landscape evolution of the Keguqin mountain and the northern Yili basin. Our results suggest that this region underwent three stages of accelerated cooling/exhumation in the Permian, Late Triassic-Jurassic and Cretaceous. The Permian cooling event likely reflects post magmatic cooling related to the Paleozoic orogeny of the Tian Shan. Late Triassic-Jurassic exhumation is possibly a far field response of the Qiangtang collision. The Cretaceous differential exhumation in the study area was controlled by activation of the Kashihe fault zone and secondary faults. As the Cretaceous cooling is widely observed in the vast Central Asia region, northern Tibet and Southern Pamir, and coeval with the Mongol-Okhotsk orogeny, Qiangtang collision and Karakorum collision. It is difficult to decipher the tectonic drive of the Cretaceous activation of the Kashihe fault zone. Relict landscapes in the Keguqin mountain were firstly established after the Paleozoic, slightly exhumed during the Cretaceous, and were uplifted and tilted by Late Cenozoic deformation. The latest uplift magnitude of the Keguqin mountain is estimated to be ∼250–500 m and ∼ 380–430 m of the hanging wall of the Kashihe fault zone and the Keguqin fault, respectively.

Multivariate analysis reveals spatial variability of soil geochemical signals in the area of a medieval manorial farm

This study presents the results of a multi-element and multivariate geochemical analysis of a deserted medieval settlement and its agricultural landscape, including a monastic (Cistercian) manorial farm, situated in the Czech Republic. We used LiDAR survey and historic maps to detect relict landscape features and identify past changes in land use-patterns. Comparing archaeological evidence and soil chemistry, we found that geochemical signals - derived from samples collected in the courtyard of the farm and in the surrounding area and processed by PCA on log-transformed and isometrically log-transformed data - responded to different agricultural activities, which could be linked to the farm and - more broadly - to current and past land-uses. The results generally illuminate the environmental impact of monastic settlement in a marginal landscape, with regard to different economic activities, and the study also demonstrates that this type of analysis allows tracing anthropogenic and natural phenomena over a wider area, beyond the limits of the more narrowly defined archaeological site.

Lithological control on topographic relief evolution in a slow tectonic setting (Anti-Atlas, Morocco)

Topographic relief results from the complex interactions between tectonics and erosional surface processes, which are primarily mediated by bedrock erodibility and climatic conditions. Ancient orogens offer a favourable setting to isolate the contribution of lithology, as tectonically driven rock uplift is typically negligible and rock strength variability can exert a critical role on the evolution of the topography. The Anti-Atlas in NW Africa is a late Paleozoic orogen comprising a well-preserved, elevated, relict landscape delimited by non-lithological knickpoints, that was uplifted during a regional late Cenozoic phase of topographic rejuvenation. Here, we combine a geomorphic analysis with 10Be-derived denudation rates to quantify bedrock erodibility and get insight into the surface evolution of the Anti-Atlas and the adjacent Siroua Massif. Specifically, we show that 10Be basin-wide denudation rates for the relict landscape are rather uniform and range from 5 to 12 m/Myr. These rates agree with long-term rates estimated from different methods suggesting that the relict topography archives erosional quasi-erosional steady-state conditions at least since the latest Cretaceous. The uniformly low 10Be denudation rates in the relict topography are consistent despite the variability in channel steepness and topographic relief that correlates with changes in rock type. The expansion of this analysis to the denudation rates of the downstream portion of the landscape, allows to demonstrate a linear relationship between denudation and channel steepness for catchments draining quartz bearing lithologies. This provides the chance to constrain a narrow range of bedrock erodibility values for different rock-types (quartzite, granitic and sedimentary rocks). These values are comparable with estimates from other slowly deforming settings. Specifically, our compilation from tectonically inactive to slow tectonic regions indicates that bedrock erodibility does not change significantly across different climatic zones and precipitation regimes. This highlights the critical role of lithology in controlling the production of topographic relief in post-orogenic/slow tectonic settings. Finally, we calculate the predicted denudation rates for the steeper portions of the landscape that adjusted to the new uplift rates based on the linear correlation between erosion rates and normalized steepness indices. These rates range from 20 to 50 m/Myr and agree with the direct measurements from two catchments.

Sewage Irrigation Fields—From Relict Landscape to Blue-Green Urban Infrastructure

In this study, we examined the fate and future of sewage irrigation fields; historic urban wetlands that served as sewer drainage before modern sewage treatment plants were built. Our aim in this study was to reappraise sewage irrigation fields in the urban fabric of modern cities and to analyse the possibility of re-integrating them into the ecosystem services system, as well as into green and blue infrastructure, providing leisure and recreational opportunities, stabilising the city’s biodiversity and microclimate, and increasing water retention in these areas. The research was based on the identification of the location of sewage irrigation fields in green and blue infrastructure systems, determination of the scale and extent of their connections to the urban fabric and an analysis of their multi-functionality including: ecological, climatic, hydrological, landscape, spatial, environmental, cultural and social, educational, and tourist and recreational functions.

Knickpoint retreat and landscape preservation along main fault escarpments of the Mexican Basin and Range: The case of the southern sector of the Sierra Madre Occidental (Mexico)

Estimating how landscapes adjust to tectonic activity has been a major topic in the geomorphological research of tectonically active settings. The formation and propagation of knickpoints through the fluvial network is central to these studies since such features are a mobile boundary between a landscape adjusting to a new erosive regime, controlled by the recent tectonic activity, and a relict landscape upstream, which corresponds to the pre-existing erosive regime. The latter illustrates how landscapes can prevail across timescales ranging from ca. 101 to 106 years. We analyzed the perched landscape surfaces of the southern sector of the Sierra Madre Occidental (SMO), an igneous province mainly formed during Late Oligocene to Early Miocene tectonic extension, to confirm whether those surfaces are a relict landscape. We found that knickpoints close to main fault escarpments bounding the perched surfaces do not have significant differences in their elevation, retreat distance from grabens and half-grabens and time of migration. Moreover, the knickpoint retreat distance scales with drainage area. Our data indicate that the top surfaces of the SMO correspond to a relict landscape that contrasts with the landscape below which is in transience. The relict landscape coexists with a westward migrating tectonic activity that has produced the steepening of the landscape and the migration of mobility of divides on the southwestern sector of the SMO.

INFORMATION ON THE BRYOPHYTE FLORA OF THE BUZULUK BOR NATIONAL PARK (ORENBURG REGION)

An annotated list of bryophytes of the Buzuluk Bor National Park within Orenburg Region was compiled based on field observations, herbarium collections, and data from the literature. This territory comprises the largest pine forest in the steppe zone of Northern Eurasia and the only “island” forest area with relict landscapes in steppes on the left bank of the Volga River. The bryophyte flora of this territory is made up of 18 liverworts and 68 mosses; six of the moss species are regionally red-listed. Two previous records (Grimmia plagiopodia Hedw., Polytrichum strictum Brid.) are questionable.

Archeological Sites and Relict Landscapes as Refuge for Biodiversity: Case Study of Alexandria City, Egypt

The role of heritage sites as a shelter for biodiversity is overlooked. Eight archeological sites representing different landscapes in Alexandria City were surveyed, from which 59 stands were sampled between April 2019 and March 2021. The archeological sites and the relictual landscapes are geographically dispersed and are arranged here from west to east, representing the full range of environmental variation within the study area. The selection of stands in each site was based on the area and the variability within the habitats, the physiography, and the levels of disturbance. A composite soil sample was collected from each site. Two-way indicator species analysis (TWINSPAN) and detrended correspondence analysis (DECORANA) were carried out to identify the plant communities in the study area. The recorded taxa, their national geographical distribution, life forms, habitats, chorological types, and vegetation groups are listed. A total of 221 specific taxa, 172 native and 49 alien non-native species (representing some 10.3% of the whole range of Egyptian flora), belonging to 150 genera and 44 families, are reported in the present study. Only two endemic species were recorded in the studied urban habitats. The phytosociological analysis of the sites showed differences among vegetation types found in the archeological sites as a function of the varying degrees of enthronization. A significant effect of archeological site and relictual landscape on species diversity was observed as indicated using the richness, Shannon’s and Simpson’s indices. Flat plains are substantially more diverse than any of the other habitats in the present study, followed by the habitat of rocky ridge slope. The present study found evidence of an ecological legacy that persists today within the semi-arid climatic ecosystem of Alexandria City. The study highlights the urgent need for measures to maintain cultural landscapes while considering the conservation of biodiversity within the archeological sites. It is hoped that the outcomes of the current study can provide guidance on the potential integration of biodiversity conservation in planning the management of archeological sites.

Climate or tectonics? What controls the spatial-temporal variations in erosion rates across the Eastern Cordillera of Colombia?

Linking the long-term with the short-term exhumation history of a mountain range is vital for understanding the evolution of orogenic topography. Further, erosion rates could be controlled by the variability of climatic and/or tectonic processes over geological time. For example, in the Eastern Cordillera of the Colombian Andes, until recently climate forcing has been hypothesized as the primary driver of rapid Pliocene exhumation rates. In this contribution, we test this climate forcing hypothesis by integrating geomorphic, seismic, geological and published low-temperature thermochronological (Apatite Fission-Track; AFT), and cosmogenic nuclide (CN) data to quantitatively test the correlation of the spatial patterns of exhumation/erosion with either a tectonic or climatic forcing. From a regional perspective, both the long- and short-term erosion rates (derived from AFT and CN data, respectively) have a reasonable correlation with the seismic strain rates and local relief, whereas the contribution of the short-term rainfall patterns to exhumation (and denudation) is either weak or non-existent. For the Eastern Cordillera, tectonism through seismic deformation therefore seems to be a more critical driver of the topographic evolution of the range when compared with the climate variable. To deepen our investigation, we subdivided the study area into six subregions and performed a detailed statistical analysis. In one out of the six subregions (SEC2E), in the Quetame Massif area, short-term rainfall data is well correlated with the computed erosion rates. Nevertheless, the ten-fold difference between the long-term (2.36 km/Myr) and the current (0.27 km/Myr) denudation rates suggest they are strongly decoupled. The remaining five subregions featured varied correlations suggesting that the tectonic-climatic characteristics of each area must be considered and that effective local controls, such as rainfall in subzone SEC2E, cannot be extrapolated to the whole range. Finally, we discuss the tectonic implications of our findings, stressing how tectonic inheritance, typical of inversion orogens such as the Eastern Cordillera, is critical for understanding the spatial variability in exhumation/erosion rates and surface uplift. For instance, we reconstructed the paleoprofiles of four rivers (the Duda, Ariari, Guayuriba, and Guatiquía Rivers), draining the Sumapaz and Chingaza relict landscapes, on the hanging wall of the Servitá Fault, the typical example of an inverted structure. In this way, we evidenced a net surface uplift of at least 1.4 km since the late Miocene, which we speculate primarily controlled by the Servitá Fault. These findings have first-order implications as they provide evidence for Pliocene to Pleistocene landscape rejuvenation driven by tectonically inverted faults.

Hydro-Stratigraphic Conditions and Human Activity Leading to Development of a Sinkhole Cluster in a Mediterranean Water Ecosystem

Salento Peninsula (Apulia, southern Italy) is characterised by many active sinkholes, which represent the main geological hazard. The stretch of coastline between the village of Casalabate and Le Cesine wildlife reserve is highly affected, with a system of dunes separating the low beach from extensive wetlands, which were subject to uncontrolled urban development after reclamation. The overall morphology is characterized by flat topography, whilst from a hydrogeological standpoint, the mixing of inland freshwater with advancing brackish water favours the higher aggressivity with respect to soluble rocks, and the development of enhanced dissolution (hyperkarst). The relict landscapes within the protected areas still allow for the recognition of actively occurring sinkholes, which cause damage to houses, the road network and infrastructures. In this article the case of Aquatina di Frigole is described, where in the last 15 years numerous sinkholes have formed, with the processes still in rapid evolution. Detailed surveys allow for to identification of the mechanisms of sinkhole formation (suffusion sinkholes), the deriving cluster, and the main hydrogeological links among the different water bodies in the area. Acquatina di Frigole provides an excellent natural laboratory to observe development and evolution of sinkholes, and their relationships with the stratigraphic and hydrogeological elements.

Interactions between deforestation, landscape rejuvenation, and shallow landslides in the North Tanganyika–Kivu rift region, Africa

Abstract. Deforestation is associated with a decrease in slope stability through the alteration of hydrological and geotechnical conditions. As such, deforestation increases landslide activity over short, decadal timescales. However, over longer timescales (0.1–10 Myr) the location and timing of landsliding is controlled by the interaction between uplift and fluvial incision. Yet, the interaction between (human-induced) deforestation and landscape evolution has hitherto not been explicitly considered. We address this issue in the North Tanganyika–Kivu rift region (East African Rift). In recent decades, the regional population has grown exponentially, and the associated expansion of cultivated and urban land has resulted in widespread deforestation. In the past 11 Myr, active continental rifting and tectonic processes have forged two parallel mountainous rift shoulders that are continuously rejuvenated (i.e., actively incised) through knickpoint retreat, enforcing topographic steepening. In order to link deforestation and rejuvenation to landslide erosion, we compiled an inventory of nearly 8000 recent shallow landslides in © Google Earth imagery from 2000–2019. To accurately calculate landslide erosion rates, we developed a new methodology to remediate inventory biases linked to the spatial and temporal inconsistency of this satellite imagery. Moreover, to account for the impact of rock strength on both landslide occurrence and knickpoint retreat, we limit our analysis to rock types with threshold angles of 24–28∘. Rejuvenated landscapes were defined as the areas draining towards Lake Kivu or Lake Tanganyika and downstream of retreating knickpoints. We find that shallow landslide erosion rates in these rejuvenated landscapes are roughly 40 % higher than in the surrounding relict landscapes. In contrast, we find that slope exerts a stronger control on landslide erosion in relict landscapes. These two results are reconciled by the observation that landslide erosion generally increases with slope gradient and that the relief is on average steeper in rejuvenated landscapes. The weaker effect of slope steepness on landslide erosion rates in the rejuvenated landscapes could be the result of three factors: the absence of earthquake-induced landslide events in our landslide inventory, a thinner regolith mantle, and a drier climate. More frequent extreme rainfall events in the relict landscapes, and the presence of a thicker regolith, may explain a stronger landslide response to deforestation compared to rejuvenated landscapes. Overall, deforestation initiates a landslide peak that lasts approximately 15 years and increases landslide erosion by a factor 2 to 8. Eventually, landslide erosion in deforested land falls back to a level similar to that observed under forest conditions, most likely due to the depletion of the most unstable regolith. Landslides are not only more abundant in rejuvenated landscapes but are also smaller in size, which may again be a consequence of a thinner regolith mantle and/or seismic activity that fractures the bedrock and reduces the minimal critical area for slope failure. With this paper, we highlight the importance of considering the geomorphological context when studying the impact of recent land use changes on landslide activity.

Quantifying Normal Fault Evolution from River Profile Analysis in the Northern Basin and Range Province, Southwest Montana, USA

Abstract Over the past few decades, tectonic geomorphology has been widely implemented to constrain spatial and temporal patterns of fault slip, especially where existing geologic or geodetic data are poor. We apply this practice along the eastern margin of Bull Mountain, Southwest Montana, where 15 transient channels are eroding into the flat, upstream relict landscape in response to an ongoing period of increased base level fall along the Western North Boulder fault. We aim to improve constraints on the spatial and temporal slip rates across the Western North Boulder fault zone by applying channel morphometrics, cosmogenic erosion rates, bedrock characteristics, and calibrated reproductions of the modern river profiles using a 1-dimensional stream power incision model that undergoes a change in the rate of base level fall. We perform over 104 base level fall simulations to explore a wide range of fault slip dynamics and stream power parameters. Our best fit simulations suggest that the Western North Boulder fault started as individual fault segments along the middle to southern regions of Bull Mountain that nucleated around 6.2 to 2.5 Ma, respectively. This was followed by the nucleation of fault segments in the northern region around 1.5 to 0.4 Ma. We recreate the evolution of the Western North Boulder fault to show that through time, these individual segments propagate at the fault tips and link together to span over 40 km, with a maximum slip of 462 m in the central portion of the fault. Fault slip rates range from 0.02 to 0.45 mm/yr along strike and are consistent with estimates for other active faults in the region. We find that the timing of fault initiation coincides well with the migration of the Yellowstone hotspot across the nearby Idaho-Montana border and thus attribute the initiation of extension to the crustal bulge from the migrating hotspot. Overall, we provide the first quantitative constraints on fault initiation and evolution of the Western North Boulder fault, perhaps the farthest north basin in the Northern Basin and Range province that such constraints exist. We show that river profiles are powerful tools for documenting the spatial and temporal patterns of normal fault evolution, especially where other geologic/geodetic methods are limited, proving to be a vital tool for accurate tectonic hazard assessments.

Seepage Erosion in the Luquillo Mountains, Puerto Rico, Relict Landscapes

AbstractSeminal research into geomorphic shaping of landscapes by emerging groundwater suggest that the relationships governing channel form and incision rate are distinct from other fluvial systems (Howard, 1995; Dunne, 1980, 1990). While some recent work has connected these models to natural settings (Abrams et al., 2009; Petroff et al., 2011), other studies have shown that seepage erosion may be erroneously invoked in landscapes shaped by flooding and overland flow (Lamb et al., 2006, 2007). We investigate the impact of seepage erosion on the geomorphology of a tropical mountain watershed, the Rio Blanco in the Luquillo Mountains of northern Puerto Rico. We focus on a population of amphitheater‐shaped channels that incise into deeply weathered saprolite profiles in the upland reaches of the watershed, where the river is disconnected from regional base‐level lowering (Brocard et al., 2015, 2016). We measured high rates of baseflow from springs feeding these catchments, despite their small drainage areas. We constructed an empirical model relating baseflow discharge to catchment area within the watershed. We quantified long‐term (103‐104 yrs) catchment erosion from 10Be in sediment and measured the short‐term volumetric flux of bedload transport at baseflow. Rates of transport and erosion in this group of channels scale linearly with the feeding drainage area and baseflow discharge. This finding supports a stream incision model proposed for groundwater‐driven channels (Howard, 1995). We propose that deepening saprolite and coincident entrenchment of the subsurface water‐routing system initiated seepage erosion and are actively expanding the headwaters in the Rio Blanco.