Glacier lake outburst floods (GLOFs) initiate with the rapid outburst of a glacier lake, endangering downstream populations, land, and infrastructure. The flow initiates as a mud flow; however, with ...the entrainment of additional solid material, the flood will often transform into a debris flow. As the run-out slope flattens, the coarse solid material deposits and the flow de-waters. The flow transforms back into a muddy, hyperconcentrated flow of fine sediments in suspension. These flow transitions change the flow composition dramatically and influence both the overall mass balance and flow rheology of the event. In this paper, we apply a two-phase/layer model to simulate flow transitions, solid–fluid phase separations, entrainment, and run-out distances of glacier lake outburst floods. A key feature of the model is the calculation of dilatant actions in the solid–fluid mixture which control flow transitions and phase separations. Given their high initial amount of fluid within the flow, GLOFs are sensitive to slope changes inducing flow transitions, which also implies changes in the flow rheology. The changes in the rheology are computed as a function of the flow composition and do not need any adaptation by ad-hoc selection of friction coefficients. This procedure allows the application of constant rheological input parameters from initiation to run-out. Our goal is to increase the prediction reliability of debris flow modeling. We highlight the problems associated with initial and boundary (entrainment) conditions. We test the new model against the well-known Lake 513 (Peru, 2010), Lake Palcacocha (Peru, 1941), and Lake Uchitel in the Aksay Valley (Kyrgyzstan) GLOF events. We show that flow transition modeling is essential when studying areas that have significant variations in slope.
In Greenland, snow avalanches have been recognized as a significant hazard and a risk to communities for decades. However, prior to this study, no formal avalanche database nor avalanche forecasting ...service existed in Greenland. This study was conducted over the 2021–2022 snow season to advance snow science research in Greenland and provide the town of Sisimiut with an avalanche bulletin service based on snowpack stability, weather conditions, and avalanche activity monitoring data within the Sisimiut backcountry. Snowpack stratigraphies were assessed and stability tests were performed periodically using standardized methods, and the results were linked with daily weather monitoring and avalanche event characterization. The observed avalanche activity was dominated by slab avalanches, accounting for 96% of the registered events. Instabilities were mainly driven by specific temperature patterns, strong winds, and rain episodes. During cold and calm periods, slow kinetic growth of snow crystals in low-density layers was observed. Abrupt thermal increases were recurrent, resulting in softening of superficial slabs with consequent reactivation of buried weak layers, thus reducing snowpack stability. On the other hand, prolonged warmer temperatures lowered the thermal gradient within the snowpack, leading to rounding and bonding of weak layer grains, thus recovering the snowpack stability. As observed on three occasions, rain events caused the formation of persistent weak layers and should be considered a warning for future snowpack instability. As a result of this study, we retroactively linked local weather patterns with snowpack instability and provided the first periodical avalanche bulletin service for Sisimiut.
Rock glaciers are creeping periglacial landforms experiencing strong acceleration during recent atmospheric warming and raising concerns with regard to their future behaviour and stability. High ...resolution kinematic observations show strong seasonal and multi-annual variations in rock glacier creep, but the linking mechanisms to environmental forcing remain poorly understood and lack quantitative models. Here we investigate the interaction between rock glacier creep and climatic forcing - temperature and precipitation - by developing a novel conceptual and numerical modelling approach. The model is constrained and the results are compared with data from the Dirru Rock Glacier (Vallis - CH). We are able to reproduce the observed velocity variations both in magnitude and phase on seasonal and inter-annual time scales. We find that water from liquid precipitation and snow melt, rather than air temperature, is the main driver of variations in rock glacier creep. Our results imply that the influence of water on rock glacier creep is fundamental and must be considered when investigating the historic and future evolution of rock glaciers.
•Seven years of continuous in-situ observations for Dirru Rock Glacier.•Surface velocity is the combination of different superimposed signals.•Our process based model can reproduce velocity variations both in magnitude and phase.•Flow variations are governed by water, rather than air and ground temperature.•Rock glacier dynamics is complex and its coupling to climate strongly non-linear.
•We develop a 3D material point method based on finite strain elastoplasticity.•The parameters possess a strong physical meaning, allowing a priori calibration.•We reproduce four full-scale, well ...documented, historical cascading events.•Complex processes naturally emerge from the simulations, granting accurate results.
Alpine mass movements can generate process cascades involving different materials including rock, ice, snow, and water. Numerical modelling is an essential tool for the quantification of natural hazards. Yet, state-of-the-art operational models are based on parameter back-calculation and thus reach their limits when facing unprecedented or complex events. Here, we advance our predictive capabilities for mass movements and process cascades on the basis of a three-dimensional numerical model, coupling fundamental conservation laws to finite strain elastoplasticity. In this framework, model parameters have a true physical meaning and can be evaluated from material testing, thus conferring to the model a strong predictive nature. Through its hybrid Eulerian–Lagrangian character, our approach naturally reproduces fractures and collisions, erosion/deposition phenomena, and multi-phase interactions, which finally grant accurate simulations of complex dynamics. Four benchmark simulations demonstrate the physical detail of the model and its applicability to real-world full-scale events, including various materials and ranging through five orders of magnitude in volume. In the future, our model can support risk-management strategies through predictions of the impact of potentially catastrophic cascading mass movements at vulnerable sites.
This study investigates rock glacier destabilization based on the results of a unique in situ and remote-sensing-based monitoring network focused on the kinematics of the rock glacier in Äußeres ...Hochebenkar (Austrian Alps). We consolidate, homogenize, and extend existing time series to generate a comprehensive dataset consisting of 14 digital surface models covering a 68-year time period, as well as in situ measurements of block displacement since the early 1950s. The digital surface models are derived from historical aerial imagery and, more recently, airborne and uncrewed-aerial-vehicle-based laser scanning (ALS and ULS, respectively). High-resolution 3D ALS and ULS point clouds are available at annual temporal resolution from 2017 to 2021. Additional terrestrial laser scanning data collected in bi-weekly intervals during the summer of 2019 are available from the rock glacier front. Using image correlation techniques, we derive velocity vectors from the digital surface models, thereby adding rock-glacier-wide spatial context to the point-scale block displacement measurements. Based on velocities, surface elevation changes, analyses of morphological features, and computations of the bulk creep factor and strain rates, we assess the combined datasets in terms of rock glacier destabilization. To additionally investigate potential rotational components of the movement of the destabilized section of the rock glacier, we integrate in situ data of block displacement with ULS point clouds and compute changes in the rotation angles of single blocks during recent years. The time series shows two cycles of destabilization in the lower section of the rock glacier. The first lasted from the early 1950s until the mid-1970s. The second began around 2017 after approximately 2 decades of more gradual acceleration and is currently ongoing. Both destabilization periods are characterized by high velocities and the development of morphological destabilization features on the rock glacier surface. Acceleration in the most recent years has been very pronounced, with velocities reaching 20–30 m a−1 in 2020–2021. These values are unprecedented in the time series and suggest highly destabilized conditions in the lower section of the rock glacier, which shows signs of translational and rotational landslide-like movement. Due to the length and granularity of the time series, the cyclic destabilization process at the Äußeres Hochebenkar rock glacier is well resolved in the dataset. Our study highlights the importance of interdisciplinary, long-term, and continuous high-resolution 3D monitoring to improve process understanding and model development related to rock glacier rheology and destabilization.
Monitoring of the periglacial environment is relevant for many disciplines including glaciology, natural hazard management, geomorphology, and geodesy. Since October 2022, Rock Glacier Velocity (RGV) ...is a new Essential Climate Variable (ECV) product within the Global Climate Observing System (GCOS). However, geodetic surveys at high elevation remain very challenging due to environmental and logistical reasons. During the past decades, the introduction of low-cost global navigation satellite system (GNSS) technologies has allowed us to increase the accuracy and frequency of the observations. Today, permanent GNSS instruments enable continuous surface displacement observations at millimetre accuracy with a sub-daily resolution.
Background
Atrial fibrillation (AF) is the commonest supraventricular arrhythmia in chronic heart failure (CHF) with impaired left ventricular (LV) systolic function, The causes of its high incidence ...and prevalence in CHF are only partially understood.
Aim
To analyze the hemodynamic determinants of incident atrial fibrillation in CHF patients. Particulary, whether indexes of arterial stiffness might identify patients at risk for new onset AF.
Methods
77 patients (mean age 62.8±9.3 years, ejection fraction 34.5±8.3%, male 80%) were enrolled. All patients underwent a complete echocardiographic-Doppler evaluation. Aortic-pulse wave velocity (PWV) was determined by Doppler flow recordings as previously reported. Effective arterial elastance (Ea) was estimated as end-systolic pressure/ stroke volume (SV). Total arterial compliance (SAC) was calculated as SV/PP.
Results
15 (19.5%) patients developed AF during the follow up. There were no differences in age, SBP, DBP, PP, LV-EF, left atrial volume, plasma neurohormones and procollagens. Those with AF had higher aortic-PWV (7.0±2.5 vs 5.3±1.9 m/sec, p= 0.004), higher Ea (1.68±0.46 vs 1.35±0.47 mmHg/mL, p=0.03), lower SAC (1.57±0.55 vs 1.96±0.53 mL/ mmHg, p=0.02), higher time difference between pulmonary vein Ar-wave and mitral A-wave duration (PV-Ar-A) (43.5±44.2 vs 10±34.7 ms, p=0.02) and mitral E-wave velocity (0.76±0.23 vs 0.59±0.24 m/s, p=0.02). In bivariate logistic regression models aortic-PWV predicted always independently incident AF:
Variables
OR
95% CI
p-value
Aortic-PWV
1.4
1.07–1.94
0.01
SAC
0.3
0.07–0.96
0.04
Aortic-PWV
1.5
1.09–1.97
0.01
Ea
2.9
0.95–8.9
0.06
Aortic-PWV
1.9
1.2–3.0
0.003
PV-Ar-A
1.04
1.0–1.07
0.01
Conclusion
Aortic stiffness independently predicts incident AF in CHF with impaired LV-systolic function.
Mitral regurgitation (MR) after acute myocardial infarction (AMI) is an important prognostic factor. Although its mechanisms are still debated, ventricular remodeling probably plays an important ...role. Because myocardial viability (MV) in the infarct zone reduces infarct expansion and ventricular remodeling, it is also possible that its presence counteracts the development of mitral regurgitation in infarcted patients. To evaluate this issue 191 patients with uncomplicated AMI, wall motion abnormalities (akinesis) and semiquantitative evaluation of MR were retrospectively selected from those consecutively examined at our echo-laboratory to evaluate MV using low-dose dobutamine echocardiography (DbE). Follow-up evaluation was performed at 30±13 months. Seventy-nine patients had no MR; 86 patients had grade 1 MR, 11 patients had grade 2 MR, nine patients had grade 3 MR, and six patients had grade 4 MR. Patients with significant MR (>grade 1) were older (63±7 vs. 59±10 years,
P=0.03), had lower reduction of RWMSI (ΔRWMSI) during DbE (0.08±0.11 vs. 0.22±0.28,
P=0.01), more stenotic vessels at coronary angiography (2.35±0.93 vs. 1.67±1.12,
P=0.01), and more frequently had anterior–inferior AMI (
P<0.0001); they also had a non-significant tendency to higher RWMSI (2.04±0.38 vs. 1.92±0.28,
P=0.06). In a multivariate regression analysis, ΔRWMSI proved to be significantly related to the grade of MR (
P=0.02). Eighteen patients died during follow-up. Death was more frequent in patients with MR (10/165 vs. 8/26,
P=0.0003). At multivariate stepwise Cox regression analysis both the extent of ventricular dysfunction and the presence of MR were significantly related to mortality (
P<0.0001 and
P=0.01, respectively); ΔRWMSI showed a non-significant tendency to influence mortality (
P=0.09). When MR was excluded from the multivariate analysis, ΔRWMSI remained significantly related to mortality (
P=0.05). In conclusion our study suggests that the presence of MV in infarcted patients influences the development of MR. This reduction of MR may be one of the mechanisms by which MV affects mortality after AMI and should be considered in all studies that evaluate MV after myocardial infarction.
Chronic heart failure is a multi-etiological cardiovascular disorder with high prevalence and poor prognosis. Medical treatment of dilated cardiomyopathy is aimed at alleviating heart failure ...symptoms. Diuretics, angiotensin-converting enzyme (ACE) inhibitors and very recently, beta-blockers have been shown to have favorable effects on symptoms, exercise capacity and mortality. Growth hormone (GH) and insulin-like growth factor (IGF)-1 are involved in several physiological processes such as the control of muscle mass and function, body composition and regulation of nutrient metabolism. The role of GH and IGF-1 as modulators of myocardial structure and function is well established. Receptors for both GH and IGF-1 are expressed by cardiac myocytes; therefore, GH may act directly on the heart or via the induction of local or systemic IGF-1, while IGF-1 may act by endocrine, paracrine or autocrine mechanisms. Patients with acromegaly have an increased propensity to develop ventricular hypertrophy and cardiovascular diseases; impaired cardiac efficiency can also be observed in patients with GH deficiency. Animal models of pressure and volume overload have demonstrated up-regulation of cardiac IGF-1 production and expression of GH and IGF-1 receptors, implying that the local regulation of these factors is influenced by hemodynamic changes. Moreover, experimental studies suggest that GH and IGF-1 have stimulatory effects on myocardial contractility, possibly mediated by changes in intracellular calcium handling. Heart failure is due to ventricular dilation with inadequate wall thickening that leads to impaired cardiac performance; therefore, based on previous evidence we would expect beneficial effects from the use of GH in these patients. Several papers have highlighted the positive influence of GH in the regulation of heart development and performance. In patients with GH deficiency, GH administration dramatically improves cardiac function. In small open studies, acute and chronic GH treatment has demonstrated beneficial effects in patients with heart failure due to ischemic or idiopathic cardiomyopathy. Recently, two randomized, placebo-controlled studies did not show any significant GH-mediated improvement in cardiac performance in patients with dilated cardiomyopathy, despite significant increases in IGF-1. Acquired GH resistance might be an important feature of severe heart failure and explain the diverse responses to GH therapy observed in different patients. Whether GH treatment will finally find a place in the treatment of heart failure, and with which modalities, remains to be established.
Bioelectronics demand stretchable devices with steady performance under deformation. By combining an amphiphilic organic semiconducting polymer with tailored film processing, highly stretchable ...organic electrochemical transistors are demonstrated.
