Shallow Regions Research Articles

Rapid magma ascent beneath La Palma revealed by seismic tomography

For the first time, we obtained high-resolution images of Earth's interior of the La Palma volcanic eruption that occurred in 2021 derived during the eruptive process. We present evidence of a rapid magmatic rise from the base of the oceanic crust under the island to produce an eruption that was active for 85 days. This eruption is interpreted as a very accelerated and energetic process. We used data from 11,349 earthquakes to perform travel-time seismic tomography. We present high-precision earthquake relocations and 3D distributions of P and S-wave velocities highlighting the geometry of magma sources. We identified three distinct structures: (1) a shallow localised region (< 3 km) of hydrothermal alteration; (2) spatially extensive, consolidated, oceanic crust extending to 10 km depth and; (3) a large sub-crustal magma-filled rock volume intrusion extending from 7 to 25 km depth. Our results suggest that this large magma reservoir feeds the La Palma eruption continuously. Prior to eruption onset, magma ascended from 10 km depth to the surface in less than 7 days. In the upper 3 km, melt migration is along the western contact between consolidated oceanic crust and altered hydrothermal material.

An insight into the evolution of the lithospheric mantle of south Saharan metacraton: Mantle xenoliths from Jabal Eghei Volcanic Complex, Libya

An insight into the evolution of the lithospheric mantle of south Saharan metacraton: Mantle xenoliths from Jabal Eghei Volcanic Complex, Libya

Recent volcanic activity at the Asama volcano and long-period seismic signals.

Modern observation systems composed of seismic, geodetic, other geophysical, and geochemical networks developed in and around volcanic areas provide a mass of knowledge about volcanic activities. This paper summarizes the magma pathway and recent volcanic activity of the Asama volcano. The seismic velocity structure beneath the Asama volcano was investigated via seismic ambient noise tomography and active source seismic tomography. The magma pathway in the upper crust beneath the Asama volcano was synthesized by combining the velocity structure with a hypocenter distribution of volcanic earthquakes and ground deformations before and after eruptions. Temporal evolutions of multidiscipline data regarding the volcanic activity from October 2003 to January 2018 revealed that the supplied amount of magma from the magma chamber and the internal condition in the shallow regions of the conduit controlled the recent eruptions.

Spatial Evolution of Skewness and Kurtosis of Unidirectional Extreme Waves Propagating over a Sloping Beach

The understanding of the occurrence of extreme waves is crucial to simulate the growth of waves in coastal regions. Laboratory experiments were performed to study the spatial evolution of the statistics of group-focused waves that have a relatively broad-banded spectra propagating from intermediate water depth to shallow regions. Breaking waves with different spectral types, i.e., spectral bandwidths and wave nonlinearities, were generated in a wave flume using the dispersive focusing technique. The non-Gaussian behavior of the considered wave trains was demonstrated by the means of the skewness and kurtosis parameters estimated from a time series and was compared with the second-order theory. The skewness and kurtosis parameters were found to have an increasing trend during the focusing process. During both the downstream wave breaking and defocusing process, the wave train dispersed again and became less steep. As a result, both skewness and kurtosis almost returned to their initial values. This behavior is clearer for narrower wave train spectra. Additionally, the learning algorithm multilayer perceptron (MLP) was used to predict the spatial evolution of kurtosis. The predicted results are in satisfactory agreement with experimental findings.

Circulation and Transport Processes during an Extreme Freshwater Discharge Event at the Tagus Estuary

During the winter of 2013, the Tagus estuary was under the influence of intense winds and extreme freshwater discharge that changed its hydrodynamics and, consequently, the salt and heat transport. Moreover, the dynamics of the estuary may change due to climate change which will increase the frequency of heat waves and increase the mean sea level. Therefore, it is of utmost importance to study the impact of the future increase in air temperature and mean sea level under extreme events, such as that in the winter of 2013, to ascertain the foreseen changes in water properties transport within the estuary and near coastal zone. Several scenarios were developed and explored, using the Delft3D model suite, considering the results of the CMIP6 report as forcing conditions. Before the event, the mixing region of the estuary presented well-mixed conditions and its marine area a slight stratification. During the event, the estuary was filled with freshwater and the mixing region migrated toward the coast, leading to lower water temperature values inside the estuary. SLR has a higher impact on the salinity and stratification patterns than the air temperature increase. The response of water temperature is directly related to the increase in air temperature. The estuary mouth and the shallow regions will be more prone to changes than the upstream region of the estuary. The projected changes are directly linked to the future CO2 emissions scenarios, being intensive with the highest emission scenario.

Analysis of the Hydrogeological Conditions Affecting Fault Response to Nearby Hydraulic Fracturing

AbstractThe response of critically stressed dormant faults to fluid perturbation, by oil and gas production, has been a major public concern because of its link to induced seismicity. In this paper, we study the hydrogeological factors that affect a nearby fault response, during and after hydraulic fracturing (HF) operations, evaluated by the change in Coulomb Failure Stress (CFS) and the rate of seismicity (R) through coupling solid deformation and fluid flow. Our results show that the pore pressure increases rapidly in a fault that is close (hydraulically connected) to HF operations, which might lead to its activation when the injection rate is high. When the fault is adjacent to HF but distant from it, its shallow region is subjected to a stabilizing deformation‐induced normal compressive stress and its deeper region is destabilized under extension. In this case, the fault orientation and damage zone size have a significant effect on the fault's stability and response. On the other hand, decreasing the rate of injection can either increase or decrease the CFS values depending on the fault location and the dominant stresses. Therefore, serious attention should be given to the fault position, its architecture, and the injection rate to help reduce the potential for induced seismicity from HF. Our findings are verified and confirmed using the case of the Duvernay formation in Alberta, Canada, where the reported seismic data correlate with high CFS and R values.

Broadband acoustic wave propagation in temporally variable range dependent shallow water environment

Broadband acoustic wave propagation in shallow water regions involves interactions with the sea surface, sea bottom, and the water column. The topic of shallow water acoustics in the presence of variable water column has been of interest in recent years. Experimental observations have shown the importance of the effects due to the boundaries and the sound speed profile in the water column. However, more work needs to be done to establish ground truth in numerical modeling for temporally variable water column in a range dependent environment. In this paper we examine the broadband propagation on the shelf as well as the range dependent shelf break regions to depict how temporal variability of sound speed could change the dispersion characteristics of the broadband signal. Comparison between modeled and experimental data are provided. [Work supported by ONR OA program.]

Ecological and habitat preferences of diatoms in lakes of Lützow‐Holm Bay, East Antarctica

Lakes and ponds along the Antarctic coastline provide an opportunity for palaeoclimate reconstructions to complement ice core records from the interior of the continent, including via their diatom records. Diatom palaeoecological studies in remote Antarctica are partially undermined by uncertainty concerning the relative influence of climate, water quality and substrate on diatom species assemblages. The relative abundance and distribution of diatoms across a range of substrates and water depths were analysed from nine lakes in the coastal ice-free regions of Lützow-Holm Bay, East Antarctica. Specific conductivity and sample position (whether from the shallow, littoral zone, or from deeper parts of the lake) were identified as significant variables in explaining diatom distribution, using non-metric multidimensional scaling and regression tree analysis to identify statistically significant groupings of diatom assemblages and associated environmental variables. In contrast to the significant difference between the diatom assemblages from the shallow littoral region and the lake floor at most sites, the diatom flora from different substrates in the littoral zone were not significantly different, which may be related to the extent of ice cover. Humodophila australis was the most common species in the lakes with lowest specific conductivity, whereas Halamphora vyvermaniana was associated with lake-floor habitats and Psammothidium papilio with samples from littoral zones at several sites. These observations hold significance for the interpretation of lake sediment diatom assemblages in Lützow-Holm Bay as archives of past climate and indicate that sampling strategies should consider a range of locations in lakes, with samples from the lake floor prioritised for the interpretation of sediment core diatom records.

Modeling a Wave on Mild Sloping Bottom Topography and Its Dispersion Relation Approximation

Linear wave theory is a simple theory that researchers and engineers often use to study a wave in deep, intermediate, and shallow water regions. Many researchers mostly used it over the horizontal flat seabed, but in actual conditions, sloping seabed always exists, although mild. In this research, we try to model a wave over a mild sloping seabed by linear wave theory and analyze the influence of the seabed’s slope on the solution of the model. The model is constructed from Laplace and Bernoulli equations together with kinematic and dynamic boundary conditions. We used the result of the analytical solution to find the relation between propagation speed, wavelength, and bed slope through the dispersion relation. Because of the difference in fluid dispersive character for each water region, we also determined dispersion relation approximation by modifying the hyperbolic tangent form into hyperbolic sine-cosine and exponential form, then approximated it with Padé approximant. As the final result, exponential form modification with Padé approximant had the best agreement to exact dispersion relation equation then direct hyperbolic tangent form.

Bottom-associated phytoplankton bloom and its expansion in the Arctic Ocean.

Phytoplankton production in the Arctic Ocean is increasing due to global warming-induced sea ice loss, which is generally assessed through satellite observations of surface chlorophyll. Here we show that a diatom bloom can occur near the seafloor rather than at the surface in the open Arctic Ocean. Light can reach the seafloor underlying nutrient-rich bottom water after the spring bloom because the surface water becomes oligotrophic and increases transparency in the region of shallow Arctic shelf. Our microcosm experiment demonstrated that diatoms formed a bloom when sediments on the shelf region, which contained abundant viable diatom cells, were exposed to even weak light reaching the seafloor (~1% of the surface irradiance). Repeated shipboard observations in the shelf region suggested that such bottom-associated blooms occurred occasionally and the primary production was significantly underestimated by satellite observations. The average bottom irradiance (2003-2017) in the Arctic Ocean is particularly promoted in summer in the eastern East Siberian Sea and the Foxe Basin, which were ice-covered throughout the year until the 1990s. Our results imply that hidden bottom-associated blooms are now widespread across the shallow Arctic shelf region.

Hydrodynamic analysis of floating tunnel with submerged rubble mound breakwater

Hydrodynamic analysis of floating tunnel with submerged rubble mound breakwater

A reappraisal of explosive–effusive silicic eruption dynamics: syn-eruptive assembly of lava from the products of cryptic fragmentation

Silicic volcanic eruptions range in style from gently effusive to highly explosive, and may switch style unpredictably during a single eruption. Direct observations of subaerial rhyolitic eruptions (Chaiten 2008, Cordón Caulle 2011–2012, Chile) challenged long-standing paradigms of explosive and effusive eruptive styles and led to the formulation of new models of hybrid activity. However, the processes that govern such hybrid explosive–effusive activity remain poorly understood. Here, we bring together observations of the well-studied 2011–2012 Cordón Caulle eruption with new textural and petrologic data on erupted products, and video and still imagery of the eruption. We infer that all of the activity – explosive, effusive, and hybrid – was fed by explosive fragmentation at depth, and that effusive behaviour arose from sticking and sintering, in the shallow vent region, of the clastic products of deeper, cryptic fragmentation. We use a scaling approach to determine that there is sufficient time available, during emplacement, for diffusive pyroclast degassing and sintering to produce a degassed plug that occludes the shallow conduit, feeding clastogenic, apparently effusive, lava-like deposits. Based on evidence from Cordón Caulle, and from other similar eruptions, we further argue that hybrid explosive–effusive activity is driven by episodic gas-fracking of the occluding lava plug, fed by the underlying pressurized ash- and pyroclast-laden region. The presence of a pressurized pocket of ash-laden gas within the conduit provides a mechanism for generation of harmonic tremor, and for syn-eruptive laccolith intrusion, both of which were features of the Cordón Caulle eruption. We conclude that the cryptic fragmentation models is more consistent with available evidence than the prevailing model for effusion of silicic lava that assume coherent non-fragmental rise of magma from depth to the surface without wholesale explosive fragmentation.

Deciphering organic matter distribution by source-specific biomarkers in the shallow Taiwan Strait from a source-to-sink perspective

Sedimentary organic matter (OM) in coastal systems is inherently diverse, often with multiple particulate sources and transport histories. The Taiwan Strait (TS) is a typical shallow conduit region, linking the East and South China Seas. Strong ocean currents, coastal upwellings, distal large rivers, and proximal small mountainous rivers all influence the distribution of OM in the TS. We investigated the covarying patterns in the distribution of gain size classes of sand, silt, and clay; terrestrial-sourced biomarkers (n-C27+29+31 alkanes, n-C26+28+30 fatty acids (FAs), and n-C28+30+32 alkanols); marine-sourced biomarkers (phytoplankton-derived alkenones, brassicasterol, dinosterol, and zooplankton-derived cholesterol) in sea floor sediment; indicator satellite-derived primary production (Chl-a); and water-mass indicator (sea surface temperature, SST). We used an empirical orthogonal/eigen function (EOF) analysis to distinguish the influence of four hypothetical sources that entered the TS through the north, south, west, and east boundaries. Results show that input sources from the south-bound ZMCC (Zhejiang-Fujian Coastal Current) and north-bound SCSWC (South China Sea Warm Current) had the dominant influence on the OM distributions buried in the TS. Input sources via river plumes on lateral boundaries and upwellings in the TS were the secondary factors that affected the sedimentary OM distribution. Within this source-to-sink system of multiple sources and transport processes, silt and clay were the major carriers of the OM signals. Terrestrial biomarkers and primary production (Chl-a) were associated with the two major current systems and river plumes along the edge of TS. Marine biomarkers were associated with upwellings in the interior of the TS. Our finding points out that the physical systems of ocean currents, river plumes, and upwelling not only determine the distributions of biomarkers in the TS but also determine the diversity of OM in the TS.

Cascading effects of climate change on recreational marine flats fishes and fisheries.

Tropical and subtropical coastal flats are shallow regions of the marine environment at the intersection of land and sea. These regions provide myriad ecological goods and services, including recreational fisheries focused on flats-inhabiting fishes such as bonefish, tarpon, and permit. The cascading effects of climate change have the potential to negatively impact coastal flats around the globe and to reduce their ecological and economic value. In this paper, we consider how the combined effects of climate change, including extremes in temperature and precipitation regimes, sea level rise, and changes in nutrient dynamics, are causing rapid and potentially permanent changes to the structure and function of tropical and subtropical flats ecosystems. We then apply the available science on recreationally targeted fishes to reveal how these changes can cascade through layers of biological organization—from individuals, to populations, to communities—and ultimately impact the coastal systems that depend on them. We identify critical gaps in knowledge related to the extent and severity of these effects, and how such gaps influence the effectiveness of conservation, management, policy, and grassroots stewardship efforts.

Influences of tropical monsoon and El Niño Southern Oscillations on surface chlorophyll-a variability in the Gulf of Thailand

This study investigated the seasonal variability of surface chlorophyll-a (chl-a) and the influence of the El Niño Southern Oscillation (ENSO) related to environmental parameters in the Gulf of Thailand (GoT). Monthly chl-a data from MODIS from 2002 to 2020 as well as sea surface temperature (SST), wind, precipitation, and river discharge were used in this analysis. Results from seasonal climatology and Empirical Orthogonal Function (EOF) described high chl-a concentration areas along the western to the southern coasts and near Ca Mau Cape during the northeast monsoon (NEM), and the upper GoT (UGoT), eastern coast, and the GoT mouth during the southwest monsoon (SWM), while low chl-a took place during the non-monsoon (NON). The GoT was divided into six areas based on the EOFs of chl-a, and then the correlation between chl-a variability and environmental parameters was also examined. The results suggested that chl-a in coastal and offshore areas were controlled by different mechanisms. Chl-a in coastal areas responded to precipitation and river discharge as well as the shoreward wind; meanwhile, chl-a in offshore areas correlated with SST and wind magnitude indicating the importance of water mixing and upwelling. The fluctuation of chl-a in each season related to ENSO was captured by EOF based on the seasonal anomaly. The influence of ENSO was strong during NEM and NON but minimal during SWM. El Niño/La Niña generally caused low/high precipitation and high/low SST. Moreover, El Niño/La Niña caused anomalously weak/strong wind during NEM contrary to during NON. Anomalous high/low chl-a were observed in shallow regions during El Niño/La Niña corresponding to strong/weak wind in NON. Abnormal wind under ENSO also created the shifting in the high chl-a area near Ca Mau Cape. These results have improved our understanding of monsoons and ENSO variabilities as the crucial drivers of changes in the tropical marine ecosystem in both seasonal and interannual time scales.

Uncertainty quantification of large-eddy simulation results of riverine flows: a field and numerical study

We present large-eddy simulations (LES) of riverine flow in a study reach in the Sacramento River, California. The riverbed bathymetry was surveyed in high-resolution using a multibeam echosounder to construct the computational model of the study area, while the topographies were defined using aerial photographs taken by an Unmanned Aircraft System (UAS). In a series of field campaigns, we measured the flow field of the river river across multiple transects throughout the field site using an acoustic Doppler current profiler (ADCP) and estimated using large-scale particle velocimetry of the videos taken during the operation UAS. We used the measured data of the river flow field to evaluate the accuracy of the LES-computed hydrodynamics. The propagation of uncertainties in the LES results due to the variations in the riverbed’s effective roughness height and the river’s inflow discharge was studied and showed that both parameters redistributed the flow distribution laterally and vertically in the velocity profile. For the uncertainty quantification (UQ) analyses, the polynomial chaos expansion (PCE) method was used to develop a surrogate model, which was randomly sampled sufficiently by the Monte Carlo Sampling (MCS) method to generate confidence intervals for the LES-computed velocity field. Also, Sobol indices derived from the PCE coefficients were calculated to help understand the relative influence of different input parameters on the global uncertainty of the results. The UQ analysis showed that uncertainties of LES results in the shallow near bank regions of the river were mainly related to the roughness, while the variation of inflow discharge leads to uncertainty in the LES results throughout the river, indiscriminately. Changes in discharge and bed roughness altered the flow distribution laterally and vertically in the vertical profile. Polynomial chaos expansions provided a practical approach for characterizing uncertainty in LES results of a natural river. Uncertainty in simulation results near the bank is mainly due to parameter uncertainty in bed roughness characterization. Uncertainty related to the inflow discharge dominated the overall uncertainty in LES results of the river.

Experimental Constraints on the H2O-Saturated Plagioclase Liquidus and the Storage Depth of the Izu-Oshima 1986B Basaltic Andesite Melt

High-temperature melting and crystallization experiments were carried out at pressures from 1 atm to 196 MPa and under H2O-saturated conditions on the basaltic andesite melt of the Izu-Oshima 1986B eruption (i.e., the BM melt), using a 1-atmosphere fO2-controlled furnace and an internally heated pressure vessel. These data were used to constrain the H2O-saturated plagioclase liquidus (HSPL) of the melt. The fO2 conditions were controlled by a mixed H2-CO2 gas at the Ni-NiO (NNO) buffer for the 1 atm experiments, but were not controlled for the high-pressure experiments. Plagioclase is the liquidus phase at 1 atm, whereas early saturation of Fe-Ti oxide above the plagioclase liquidus occurred in the high-pressure experiments due to the elevated fO2 conditions. The HSPL temperature decreases from 1172 ± 8°C to 1030 ± 20°C as the pressure increases from 1 atm to 196 MPa. A combination of previously proposed models for the plagioclase liquidus and melt H2O-solubility can predict the experimentally determined HSPL temperatures, even if oxidation-induced magnetite crystallization occurs. Using these models and the previously reported pre-eruptive temperature of ∼1100 ± 30°C, we estimate the pre-eruptive pressure conditions of the BM melt to be 42-32+48 MPa, which corresponds to depths of 1.9-1.4+1.9 km. The estimated depth is consistent with that of the shallow active dikes previously identified from geophysical studies, suggesting that the BM melt was derived from a small, shallow magma chamber formed in the shallow dike region.

Modeling the squeeze flow of droplet over a step

In this paper, we study the squeeze flow of a droplet confined between two plates in the presence of a step. Understanding this fluid mechanics problem is of the utmost importance particularly for nanoimprint lithography, wherein the photoresist droplets are dispensed on a substrate and imprinted and cured into a desired pattern. Often, the desired pattern includes various steps and trenches, and the droplets need to flow over. Here, we use the lubrication theory to find the instantaneous pressure and velocity fields. A volume-of-fluid advection algorithm is also used for evolving the volume fraction in time. The obtained results reveal that for step sizes comparable to the gap between plates, the squeeze flow characteristics become quite distinct across the step. Under such circumstances, the fluid finds it less expensive to reverse its flow direction toward the deep region to pass through the low-resistance zone, which leads to a net mass flow rate across the step from a shallow to deep region. Such a mass transfer is found to be enhanced by applying larger squeezing forces. This phenomenon becomes less noticeable for liquid film thicknesses much larger than the step size. As a result, it takes large droplets a longer time to reach to the regime wherein a substantial mass flow rate occurs. In addition, the results suggest that the dimensionless characteristic features, such as the ratios of volume and area of liquid in the deep (or shallow) region to those of the total liquid, collapse onto their corresponding master curves.

The A B C's of metasomatism in the North Atlantic Craton during Pangea breakup; characterized by fluid inclusions in Chidliak diamonds

The A B C's of metasomatism in the North Atlantic Craton during Pangea breakup; characterized by fluid inclusions in Chidliak diamonds

Topographic effects on buoyancy driven flows along the slope

The flow and descent of dense water masses formed in shallow regions of the ocean is an important leg in the global overturning circulation. The dense overflow waters tend to flow along the continental slopes as geostrophically balanced gravity plumes, but may be steered downslope by canyons and ridges cross-cutting the slopes. In that process, entrainment and mixing will be greatly enhanced. Ilicak et al. (Ocean Model 38:71–84, 2011) propose a parameterization to include the effects of corrugations in large scale models by increasing the vertical mixing locally. We re-visit the problem using the terrain-following Bergen Ocean Model and a DOME-inspired idealized topography. It is shown that the applied corrugations can move the core of the plume 800 m down the slope, while enhanced mixing raises the center of gravity by only 1–200 m. The overall effect of a corrugation is hence to lower the center of gravity, suggesting that the parameterization proposed by Ilicak et al. (Ocean Model 38:71–84) will act in the wrong vertical direction, if used on its own. A comparison of two bottom drag parameterizations, show that a parameterization consistent with a no-slip boundary condition is needed to correctly represent Ekman drainage, and that the Ekman drainage contribution to plume descent is comparable to that of the corrugation. Ridges are more effective in steering dense water downward than canyons, and we compare the dynamics between the two settings to explain the difference.