Formation of waterfalls by intermittent burial of active faults

Waterfalls commonly exist near bounding faults of mountain ranges, where erosional bedrock catchments transition to depositional alluvial fans. We hypothesize that aggradation on alluvial fans can bury active faults, and that the faults accumulate slip in the subsurface to produce a bedrock scarp. Following entrenchment of the alluvial fan, the scarp can be exposed as a waterfall. To explore this hypothesis, we derived a geometric model for waterfall height that depends on alluvial fan length and the relative time scales of (1) tectonic uplift, (2) a forcing mechanism for cycles of fan aggradation and incision, and (3) a response of fan aggradation to changes in sediment flux. We find that the model is consistent with observations at Gower Gulch, Death Valley, California, where a man-made drainage capture event in 1941 caused rapid fan incision and exposed a waterfall at the canyon-fan transition. We also compared the model to 62 waterfalls in 18 catchments of the Death Valley area and found that at least 15 of the waterfalls are best explained by the fault-burial mechanism. Using field measurements of grain size and channel geometries, we show that the fault-burial mechanism can produce the observed waterfall heights, measuring 4−19 m, under a uniform climatic forcing scenario requiring variations of 20% in precipitation during the late Pleistocene. The fault-burial mechanism, through the creation of upstream propagating waterfalls, may allow catchment-fan systems to experience frequent cycles of enhanced erosion in catchments and deposition on fans that likely convolve tectonic and climatic signals

Modes of extensional faulting controlled by surface processes

We investigate the feedbacks between surface processes and tectonics in an extensional setting by coupling a 2-D geodynamical model with a landscape evolution law. Focusing on the evolution of a single normal fault, we show that surface processes significantly enhance the amount of horizontal extension a fault can accommodate before being abandoned in favor of a new fault. In simulations with very slow erosion rates, a 15 km thick brittle layer extends via a succession of crosscutting short-lived faults (heave 10 km). Using simple scaling arguments, we quantify the effect of surface mass removal on the force balance acting on a growing normal fault. This leads us to propose that the major range-bounding normal faults observed in many continental rifts owe their large offsets to erosional and depositional processes

Autogenic entrenchment patterns and terraces due to coupling with lateral erosion in incising alluvial channels

The abandonment of terraces in incising alluvial rivers can be used to infer tectonic and climatic histories. A river incising into alluvium erodes both vertically and laterally as it abandons fill-cut terraces. We argue that the input of sediment from the valley walls during entrenchment can alter the incision dynamics of a stream by promoting vertical incision over lateral erosion. Using a numerical model, we investigate how valley wall feedbacks may affect incision rates and terrace abandonment as the channel becomes progressively more entrenched in its valley. We postulate that erosion of taller valley walls delivers large pulses of sediment to the incising channel, potentially overwhelming the local sediment transport capacity. Based on field observations, we propose that these pulses of sediment can form talus piles that shield the valley wall from subsequent erosion and potentially force progressive channel narrowing. Our model shows that this positive feedback mechanism can enhance vertical incision relative to 1-D predictions that ignore lateral erosion. We find that incision is most significantly enhanced when sediment transport rates are low relative to the typical volume of material collapsed from the valley walls. The model also shows a systematic erosion of the youngest terraces when river incision slows down. The autogenic entrenchment due to lateral feedbacks with valley walls should be taken into account in the interpretation of complex-response terraces

Formation of waterfalls by intermittent burial of active faults

Waterfalls commonly exist near bounding faults of mountain ranges, where erosional bedrock catchments transition to depositional alluvial fans. We hypothesize that aggradation on alluvial fans can bury active faults, and that the faults accumulate slip in the subsurface to produce a bedrock scarp. Following entrenchment of the alluvial fan, the scarp can be exposed as a waterfall. To explore this hypothesis, we derived a geometric model for waterfall height that depends on alluvial fan length and the relative time scales of (1) tectonic uplift, (2) a forcing mechanism for cycles of fan aggradation and incision, and (3) a response of fan aggradation to changes in sediment flux. We find that the model is consistent with observations at Gower Gulch, Death Valley, California, where a man-made drainage capture event in 1941 caused rapid fan incision and exposed a waterfall at the canyon-fan transition. We also compared the model to 62 waterfalls in 18 catchments of the Death Valley area and found that at least 15 of the waterfalls are best explained by the fault-burial mechanism. Using field measurements of grain size and channel geometries, we show that the fault-burial mechanism can produce the observed waterfall heights, measuring 4−19 m, under a uniform climatic forcing scenario requiring variations of 20% in precipitation during the late Pleistocene. The fault-burial mechanism, through the creation of upstream propagating waterfalls, may allow catchment-fan systems to experience frequent cycles of enhanced erosion in catchments and deposition on fans that likely convolve tectonic and climatic signals

Autogenic entrenchment patterns and terraces due to coupling with lateral erosion in incising alluvial channels

The abandonment of terraces in incising alluvial rivers can be used to infer tectonic and climatic histories. A river incising into alluvium erodes both vertically and laterally as it abandons fill-cut terraces. We argue that the input of sediment from the valley walls during entrenchment can alter the incision dynamics of a stream by promoting vertical incision over lateral erosion. Using a numerical model, we investigate how valley wall feedbacks may affect incision rates and terrace abandonment as the channel becomes progressively more entrenched in its valley. We postulate that erosion of taller valley walls delivers large pulses of sediment to the incising channel, potentially overwhelming the local sediment transport capacity. Based on field observations, we propose that these pulses of sediment can form talus piles that shield the valley wall from subsequent erosion and potentially force progressive channel narrowing. Our model shows that this positive feedback mechanism can enhance vertical incision relative to 1-D predictions that ignore lateral erosion. We find that incision is most significantly enhanced when sediment transport rates are low relative to the typical volume of material collapsed from the valley walls. The model also shows a systematic erosion of the youngest terraces when river incision slows down. The autogenic entrenchment due to lateral feedbacks with valley walls should be taken into account in the interpretation of complex-response terraces

BioNoMo. The biodiversity network of Mozambique

Mozambique biodiversity richness plays a pivotal role to achieve the sustainable development of the country. However, Mozambique's flora and fauna diversity still remains broadly unknown and poorly documented. To properly address this issue, one of the strategic needs expressed by the Mozambican institutions was the development of a national biodiversity data repository to aggregate, manage and make data available online. Thus, a sustainable infrastructure for the standardisation, aggregation, organisation and sharing of primary biodiversity data was developed. Named the "Biodiversity Network of Mozambique" (BioNoMo), such a tool serves as a national repository of biodiversity data and aggregates occurrence records of plants and animals in the country obtained from floristic and faunistic observations and from specimens of biological collections. In this paper, the authors present the structure and data of BioNoMO, including software details, the process of data gathering and aggregation, the taxonomic coverage and the WebGIS development. Currently, aggregating a total of 273,172 records, including 85,092 occurrence records of plants and 188,080 occurrence records of animals (41.2% terrestrial, 58,8% aquatic), BioNoMo represents the largest aggregator of primary biodiversity data in Mozambique and it is planned to grow further by aggregating new datasets

In Vivo Fate Analysis Reveals the Multipotent and Self-Renewal Features of Embryonic AspM Expressing Cells

Radial Glia (RG) cells constitute the major population of neural progenitors of the mouse developing brain. These cells are located in the ventricular zone (VZ) of the cerebral cortex and during neurogenesis they support the generation of cortical neurons. Later on, during brain maturation, RG cells give raise to glial cells and supply the adult mouse brain of Neural Stem Cells (NSC). Here we used a novel transgenic mouse line expressing the CreERT2 under the control of AspM promoter to monitor the progeny of an early cohort of RG cells during neurogenesis and in the post natal brain. Long term fate mapping experiments demonstrated that AspM-expressing RG cells are multi-potent, as they can generate neurons, astrocytes and oligodendrocytes of the adult mouse brain. Furthermore, AspM descendants give also rise to proliferating progenitors in germinal niches of both developing and post natal brains. In the latter –i.e. the Sub Ventricular Zone- AspM descendants acquired several feature of neural stem cells, including the capability to generate neurospheres in vitro. We also performed the selective killing of these early progenitors by using a Nestin-GFPflox-TK allele. The forebrain specific loss of early AspM expressing cells caused the elimination of most of the proliferating cells of brain, a severe derangement of the ventricular zone architecture, and the impairment of the cortical lamination. We further demonstrated that AspM is expressed by proliferating cells of the adult mouse SVZ that can generate neuroblasts fated to become olfactory bulb neurons

How do cardiologists select patients for dual antiplatelet therapy continuation beyond 1 year after a myocardial infarction? Insights from the EYESHOT Post-MI Study

Background: Current guidelines suggest to consider dual antiplatelet therapy (DAPT) continuation for longer than 12 months in selected patients with myocardial infarction (MI). Hypothesis: We sought to assess the criteria used by cardiologists in daily practice to select patients with a history of MI eligible for DAPT continuation beyond 1 year. Methods: We analyzed data from the EYESHOT Post-MI, a prospective, observational, nationwide study aimed to evaluate the management of patients presenting to cardiologists 1 to 3 years from the last MI event. Results: Out of the 1633 post-MI patients enrolled in the study between March and December 2017, 557 (34.1%) were on DAPT at the time of enrolment, and 450 (27.6%) were prescribed DAPT after cardiologist assessment. At multivariate analyses, a percutaneous coronary intervention (PCI) with multiple stents and the presence of peripheral artery disease (PAD) resulted as independent predictors of DAPT continuation, while atrial fibrillation was the only independent predictor of DAPT interruption for patients both at the second and the third year from MI at enrolment and the time of discharge/end of the visit. Conclusions: Risk scores recommended by current guidelines for guiding decisions on DAPT duration are underused and misused in clinical practice. A PCI with multiple stents and a history of PAD resulted as the clinical variables more frequently associated with DAPT continuation beyond 1 year from the index MI