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The Himalayas stretch ∼3000 km along the Indo-Eurasian plate boundary. Along-strike variations in the fault geometry of the Main Himalayan Thrust (MHT) have given rise to significant variations in the topographic steepness, exhumation rate, and orographic precipitation along the Himalayan front. Over the past 2 decades, the rates and patterns of Himalayan denudation have been documented through numerous cosmogenic nuclide measurements in central and eastern Nepal, Bhutan, and northern India. To date, however, few denudation rates have been measured in Far Western Nepal, a ∼300 km wide region near the center of the Himalayan arc, which presents a significant gap in our understanding of Himalayan denudation. Here we report new catchment-averaged millennial-scale denudation rates inferred from cosmogenic 10Be in fluvial quartz at seven sites in Far Western Nepal. The inferred denudation rates range from 385±31 t km -2 yr -1 (0.15±0.01 mm yr -1) to 8737±2908 t km -2 yr -1 (3.3±1.1 mm yr -1) and, in combination with our analyses of channel topography, are broadly consistent with previously published relationships between catchment-averaged denudation rates and normalized channel steepness across the Himalaya. These data show that the denudation rate patterns in Far Western Nepal are consistent with those observed in central and eastern Nepal. The denudation rate estimates from Far Western Nepal show a weak correlation with catchment-averaged specific stream power, consistent with a Himalaya-wide compilation of previously published stream power values. Together, these observations are consistent with a dependence of denudation rate on both tectonic and climatic forcings, and they represent a first step toward filling an important gap in denudation rate measurements in Far Western Nepal. [ABSTRACT FROM AUTHOR]

Detailed characterization of variations in sediment production, routing, and transport processes in peri-orogenic basins offers insights into underlying external forcing mechanism from climate or tectonics. The correct interpretation of such environmental signals in the sedimentary record remains challenging and benefits greatly from high-resolution geochronology and a precise evaluation of all stratigraphic elements of the sedimentary system. Spatially averaged sediment-accumulation rates can help to investigate such environmental signals. A key area to investigate environmental signal propagation in the late Oligocene/early Miocene is the Upper Austrian Molasse Basin due to the large amount of available data in the Alpine source area and the foreland. Deep-marine sedimentation, forming the Zupfing, Puchkirchen and Hall Formation, was controlled by a basin-axial submarine channel of 3-5 km width and >100 km length. Two basin-wide unconformities were recognized in seismic-reflection data: the Northern Slope Unconformity (NSU), and the Base Hall Unconformity (BHU).We reevaluated and extended the biostratigraphic concepts of the Oligocene/Miocene Upper Austrian Molasse deposits. We used these high-resolution age constraints to determine age, duration of the unconformities and calculated spatially averaged sediment-accumulation rates. Calculations were run separately for three time intervals in submarine channel and six intervals in the overbank deposits, using a large (3300 km2) 3D seismic-reflection cube and lithology and density logs of 72 wells.Our new stratigraphic concept indicates that the NSU was formed from <28.09 to 24.5 Ma due to tectonically induced oversteepening of the northern basin slope. Sediment-accumulation rates in the channel deposits do not record any autogenic or external environmental signal. The overbank deposits, however, do record such signals. During the Puchkirchen Formation (24.5-19.6 Ma), the sediment-accumulation rates on the overbanks remained stable except for a short period from 23.5-23.1 Ma showing a fourfold increase. We interpret this increase as a result of an autogenic migration of channel-meander bends visible in the seismic-reflection data that lead to an increase in flow stripping of turbidity currents onto the overbanks. Furthermore, we detect a 0.5-fold decreased accumulation rate compared to rates in the Puchkirchen Formation above the BHU from 19.6 to 19.0 Ma. During this time, turbidity-current deposits are increasingly mud-rich and a sea-level drop is inferred from previous studies. We interpret this pattern to be related to the previously proposed visco-elastic relaxation of the European plate leading to relief reduction in the Alpine hinterland and uplift in the Molasse Basin. From 19.0 to 18.1 Ma, accumulation rates are 4.5-fold higher than in the underlying Puchkirchen Formation, which we explain by the tectonically induced uplift of the Northern Calcareous Alps and increased erosion of the overlying Augenstein Formation. In this setting, overbank deposits are more suitable to detect environmental signals than channel deposits. [ABSTRACT FROM AUTHOR]

Estimating slip rates of active faults is critical not only for assessing of seismic potential of these structures but also for understanding their geodynamics. The North Anatolian Fault (NAF) forms the boundary between Anatolia and Eurasia with the total slip rate of 24.6±0.2 mm/yr, deduced by GPS-based elastic block modelling. However, the quantification of total strain along the NAF is also a challenging problem where the fault leaves its single going narrow deformation zone and bifurcates into two strands (Düzce and Mudurnu Valley Segments) to the west of Bolu. In order to reveal the long term slip rate of the Mudurnu Valley Segment, we conducted a new slip rate study at the Taşkesti Site to the south of the Almacık Block by using high resolution UAV-based DEMs and multiple geochronological techniques. Our geological mapping shows a depositional river terrace, having a dextral offset of 52-62 metres where its age is constrained to 5.79±0.13 ka (radiocarbon) as an upper boundary and 5.36±0.19 ka (OSL) as a lower boundary. By using a boxcar uncertainty model, we calculate 10.3 +2.4/-2.3 mm/yr as the Holocene slip-rate of the Mudurnu Valley Segment. We compare our results with other nearby geodetic, and other geologic rate studies to determine (a) the total strain accumulation along the western section of the NASZ and (b) to understand the ratio of strain partitioning between Düzce and Mudurnu Valley segments. Our preliminary results strongly suggest strain partitioning between parallel/sub-parallel elements of the North Anatolian Shear Zone. The implication of this study also contributes to an understanding of the spatial and temporal slip behaviours of other major continental strike-slip faults. [ABSTRACT FROM AUTHOR]

We have used multiple independent methods to investigate the time-evolution of eruptive intensity during the Plinian phase of the 3600 y BP Bronze-Age eruption of Santorini Volcano: mass discharge rate based on new lithic isopleth maps for multiple sub-levels in the deposit, and magma decompression rate based on (1) pumice vesicle number densities, and (2) volatile gradients in plagioclase/pyroxene-hosted melt re-entrants. Using lithic data collected at 44 sites around the caldera rim, the main Plinian phase began with a 13.5 ± 3 km high plume that grew to the peak height of 27 ± 5 km, before then decreasing to 17 ± 3 km. This final decrease in plume height coincides with the first appearance of pyroclastic surge deposits in the eruption sequence. Two independent estimates for decompression rate were derived from the same pumice clast collected from each Plinian sub-level. Preliminary results from both techniques exhibit an increase in decompression rate towards the peak in plume height, followed by a sudden decrease, suggesting a positive correlation with mass discharge rate. However, the decompression rates determined from vesicle number densities (2-20 MPa/s) are two orders of magnitude higher than those obtained from melt reentrants (0.01-0.3 MPa/s). This difference suggests that the two methods may be recording decompression rates at different levels of the conduit. Melt re-entrants likely record a time-averaged integration of decompression rate between the magma reservoir and the fragmentation level, whereas vesicle number densities probably record decompression rate as the ascending magmatic foam travels through the steep pressure gradient just below the fragmentation level. These results, combined with lithic evidence for a falling fragmentation level with time during the Plinian eruption phase, provide quantitative constraints for future development of a numerical conduit model aimed at reconstructing the progression of a Plinian eruption. [ABSTRACT FROM AUTHOR]

The Filchner Ice Shelf System (FISS) located at the southern boundary of the Weddell sea buttresses the outflow of ice flows upstream. Work by Hellmer et al. (2012; 2017) suggests that the intrusion of warm circumpolar deep water in the future could lead to dramatic, irreversible changes for the ice shelf system, making the FISS system a major component of Antarctica's contribution to projected sea level rise. First-order questions remain however, as to the present day factors influencing FISS' melt rates on inter-annual timescales. Recent in-situ moorings and a seismic survey (e.g. (Rosier et al., 2018)) by the British Antarctic Survey offer an unprecedented opportunity to improve and evaluate numerical simulations of the region. Here, using eddy-permitting NEMO regional ocean model simulations with static ice-shelves, we focus on understanding the large-scale ocean and atmospheric circulation patterns that influence melt rates over the re-analysis period. In particular, we show that the remote atmospheric forcing plays a strong role in controlling Ronne's bottom water properties and modulates inter-annual melt rates. The eddy-permitting results presented shed light on the historical context of the BAS S03/S05 mooring observations and the AWI POLARSTERN FISS transects of 1980 and 1995. [ABSTRACT FROM AUTHOR]

Mount Etna volcano is well-known for its frequent eruptions and high degassing rates from its summit craters and flanks. The INGV geochemical monitoring networks for soil CO2 flux and CO2/SO2 plume variation have recorded very significant degassing variations from both the flank and the summit craters during the second half of 2018, during which several significant volcanic events occurred. A new phase of eruptions which started in August 2018 after a 16 month period of quiescence, was punctuated by two strong seismic shocks in October and December. Past observations have distinguished a tendency for high variations in degassing rates marked by a sharp increase preceding the onset of volcanic activity, however the two earthquakes with magnitudes of 4.6 (6 October) and 4.8 (26 December) are the first to have been recorded since the geochemical networks have been operative. While no interpretative model is yet available to account for such a combination of events, two important aspects regarding the 2018 eruptions and their possible relationship with degassing rates are noteworthy: first, both the networks recorded almost synchronous high variations in degassing rates; second, both the earthquakes occurred during phases of minimum gas rate variations. The 2018 period of high volcanic activity and the corresponding seismic episodes represent an invaluable first case study for Etna which combines data for both seismic shocks and geochemical signal variations. Our preliminary data provide stimulating food for thought and potential in exploring the possible interconnected dynamics between the degassing pattern and seismic activity of the volcano. [ABSTRACT FROM AUTHOR]