Stratigraphy,chronology, and character of the 1976 pyroclastic eruption of Augustine volcano,Alaska

The chronology of deposits of the 1976 eruption of Augustine volcano, which produced pyroclastic falls, pyroclastic flows, and lava domes, is determined by correlating the stratigraphy with published records of seismicity, plume observations, and distant ash falls. Three thin air-fall ash beds (unit A1, A2 and A3) correlate with events near the beginning of the 1976 eruption on 22 and 23 January. On 24 January a small-volume, ash-cloud-surge deposit (unit S) accumulated over the north half of Augustine Island. A series of pumiceous pyroclastic flows represented by the lobate pumiceous deposits (unit F) occurred on 24 January and locally melted the snowpack to cause small pumice-laden floods. A thin ash bed (unit A4) was deposited on 24 January, and the main plinian eruption (unit P) occurred on 25 January. In middle to late February and again in mid April, lava domes were extruded at the summit accompanied by incandescent block-and-ash flows down the north flank. A hut near the north coast of the island was mechanically and thermally damaged by the small-volume ash-cloud surge of unit S before the eruption of the pumice flow of unit F; the metal roof was then penetrated by lithic fragments of the plinian fall of 25 January. Explosive eruptions in the early stage of an eruption-like that which deposited unit S — are important hazards at Augustine Island, as are infrequent debris avalanches and attendant tsunamis.deceased on 18 May 1980     

Reynolds-Number Dependence of Gas Dispersion Over a Wavy Wall

Direct numerical simulations of an Ekman layer are performed to study flow evolution during the response of an initially neutral boundary layer to stable stratification. The Obukhov length, L, is varied among cases by imposing a range of stable buoyancy fluxes at the surface to mimic ground cooling. The imposition of constant surface buoyancy flux , i.e. constant-flux stability, leads to a buoyancy difference between the ground and background that tends to increase with time, unlike the constant-temperature stability case where a constant surface temperature is imposed. The initial collapse of turbulence in the surface layer owing to surface cooling that occurs over a time scale proportional to \(L/u_*\), where \(u_*\) is the friction velocity, is followed by turbulence recovery. The flow accelerates, and a “low-level jet” (LLJ) with inertial oscillations forms during the turbulence collapse. Turbulence statistics and budgets are examined to understand the recovery of turbulence. Vertical turbulence exchange, primarily by pressure transport, is found to initiate fluctuations in the surface layer and there is rebirth of turbulence through enhanced turbulence production as the LLJ shear increases. The turbulence recovery is not monotonic and exhibits temporal intermittency with several collapse/rebirth episodes. The boundary layer adjusts to an increase in the surface buoyancy flux by increased super-geostrophic velocity and surface stress such that the Obukhov length becomes similar among the cases and sufficiently large to allow fluctuations with sustained momentum and heat fluxes. The eventual state of fluctuations, achieved after about two inertial periods (\(ft \approx 4\pi \)), corresponds to global intermittency with turbulent patches in an otherwise quiescent background. Our simplified configuration is sufficient to identify turbulence collapse and rebirth, global and temporal intermittency, as well as formation of low-level jets, as in observations of the stratified atmospheric boundary layer.     

Heat-Mitigation Effects of Irrigated Rice-Paddy Fields Under Changing Atmospheric Carbon Dioxide Based on a Coupled Atmosphere and Crop Energy-Balance Model

Boundary-Layer Meteorology - Known as the heat-mitigation effect, irrigated rice-paddy fields distribute a large fraction of their received energy to the latent heat during the growing season. The...     

Comparison of different methods for estimating soil surface evaporation in a bare field

In this paper, three methods for estimating soil evaporation in a bare field were evaluated: evaporation ratio method (k ratio), complementary relationship and bulk equation. Micro-lysimeters were used to measure the actual evaporation for validation of the three methods. For the k ratio method, pan evaporation was used as the reference evaporation instead of the value obtained from the Penman–Monteith equation. This result is important for areas where meteorological data are unavailable. The results showed that, for daytime evaporation, the k ratio and bulk equation produced a good fit with the observation data, while the complementary relationship generated a larger deviation from the measured data. We recommend that the k ratio method and bulk equation could be used to calculate daytime soil evaporation with high accuracy when soil water content and pan evaporation data or meteorological data are available, while the complementary relationship could be used for a rough estimation when pan evaporation is available. All the methods could be applied to calculate cumulative evaporation.     

rare Earth Elements in Six New GSJ Standard Rock Samples as Determined by Inductively Coupled Plasma Atomic Emission Spectrometry

Analytical data of rare earth elements (REEs) are presented for six new standard rock samples (JB-2, JB-3, JR-1, JR-2, JA-1, and JGb-1) issued by the Geological Survey of Japan. These data have been simultaneously determined by inductively coupled plasma atomic emission spectrometry.     

Heating experiments of the Tagish Lake meteorite: Investigation of the effects of short‐term heating on chondritic organics

We present in this study the effects of short‐term heating on organics in the Tagish Lake meteorite and how the difference in the heating conditions can modify the organic matter (OM) in a way that complicates the interpretation of a parent body's heating extent with common cosmothermometers. The kinetics of short‐term heating and its influence on the organic structure are not well understood, and any study of OM is further complicated by the complex alteration processes of the thermally metamorphosed carbonaceous chondrites—potential analogues of the target asteroid Ryugu of the Hayabusa2 mission—which had experienced posthydration, short‐duration local heating. In an attempt to understand the effects of short‐term heating on chondritic OM, we investigated the change in the OM contents of the experimentally heated Tagish Lake meteorite samples using Raman spectroscopy, scanning transmission X‐ray microscopy utilizing X‐ray absorption near edge structure spectroscopy, and ultraperformance liquid chromatography fluorescence detection and quadrupole time of flight hybrid mass spectrometry. Our experiment suggests that graphitization of OM did not take place despite the samples being heated to 900 °C for 96 h, as the OM maturity trend was influenced by the heating conditions, kinetics, and the nature of the OM precursor, such as the presence of abundant oxygenated moieties. Although both the intensity of the 1s?σ* exciton cannot be used to accurately interpret the peak metamorphic temperature of the experimentally heated Tagish Lake sample, the Raman graphite band widths of the heated products significantly differ from that of chondritic OM modified by long‐term internal heating.     

Dynamical Features and Evolutional Characteristics of Brightening Coronal Loops

We present a detailed study of coronal loop brightenings observed in an active region on the solar limb. These brightening loops show expanding and shrinking motions in EUV coronal line images and also show downflow along the loops in Lα and Hα images. By means of time-slice analysis of the images, we found that both the expanding and shrinking motions of the loops are not real motions of plasma but apparent motions like post-flare loops, where the loops at the different height are successively heated and cooled. From a temperature analysis, the time delay between the brightenings of hot 195 Å and cool Lα loops is found to be nearly equal to the time-scale of the conduction cooling. We conclude that these loop brightenings are sources of so called Hα coronal rains.     

A hydrocode calculation coupled with reaction kinetics of carbon compounds within an impact vapor plume and its implications for cometary impacts on Galilean satellites

The synthesis of organic molecules via chemical reactions within impact vapor plumes has been proposed as a mechanism to supply organics on a planet. However, the kinetics of chemical reactions within a rapidly expanding vapor plume or quenching process of the reactions has not been studied extensively. In this study, we constructed a new numerical model that calculates kinetics of the entire chemical reactions within an impact vapor plume. Numerical results revealed that the semi-analytical models proposed so far, in which the final amount of a chemical species was given by the equilibrium abundance at the quenching temperature of the fastest reaction path involving the species, underestimates the yield of organic molecules, such as HCN, by up to a factor of 10. This is because the previously used assumption that a species can achieve equilibrium with the rest of the reaction system via the fastest reaction path involving the species is not necessarily valid. Our analysis of the high-temperature H/C/N/O reaction system suggests that the quenching of slow reactions divides the reaction network into smaller reaction sub-systems isolated from the rest of the reaction system. Then, the fastest reaction path cannot equilibrate an isolated reaction sub-system with the rest of the reaction system. Simulation of this actual disequilibrium mechanism requires a simultaneous numerical calculation of the entire reaction network, which is equivalent to conducting a full kinetic model calculation, such as our model. Our numerical code makes it possible to discuss quantitatively the impact chemistry for various situations, such as the Galilean satellites. In this study, our numerical model is applied to the delivery of organic molecules via cometary impact on the Galilean satellites. Our numerical results indicate that small-particle impacts would produce HCN efficiently. Resulting HCN may freeze out immediately and be deposited on satellite surfaces, where it may be eventually converted into complex organics via irradiation of charged particle. On the other hand, large-size impacts may form transient CH₄-N₂ atmospheres, in which complex organics (tholin) may be formed via energy deposition of UV and/or charged particle. Resulting complex organics may subsequently precipitate on the satellite surfaces without clear correlation with the locations of impact craters. Such distribution of complex organics created by chemical reactions within vapor plumes due to cometary impacts may explain an absorption (4.57 μm) on Galilean satellites nonassociated with observable (moderate- and large-size) impact craters.     

Role of tonalite-trodhjemite-granite (TTG) crust subduction on the mechanism of supercontinent breakup

The tonalite-trondhjemite-granite (TTG) crust has been considered to be buoyant and hence impossible to be subducted into the deep mantle. However, recent studies on the juvenile arc in the western Pacific region indicate that immature island arcs subduct into the deep mantle in most cases, except in the case of parallel arc collision. Moreover, sediment trapped subduction and tectonic erosion are also common. This has important implications in evaluating the role of TTG crust in the deep mantle and probably on the bottom of the mantle. Because the TTG crust is enriched in K, U and Th, ca. 20 times more than that of CI chondrite, the accumulated TTG on the Core Mantle Boundary (CMB) would have played a critical role to initiate plumes or superplumes radiating from the thermal boundary layer, particularly after 2.0 Ga, related to the origin of superplume-supercontinent cycle. This is because selective subduction of oceanic lithosphere including sediment-trapped subduction, tectonic erosion and arc- and microcontinent-subduction proceeded under the supercontinent before the final amalgamation ca. 200-300 million years after the formation of the nuclei. We speculate the mechanism of superplume evolution through the subduction of TTG-crust and propose that this process might have played a dominant role in supercontinent breakup.     

Shock-wave compression of silica gel as a model material for comets

A shock-wave compression experiment using synthesized silica gel was investigated as a model for a comet impact event on the Earth’s surface. The sample shocked at 20.7 GPa showed considerable structural changes, a release of water molecules, and the dehydration of silanol (Si–OH) that led to the formation of a new Si–O–Si network structure containing larger rings (e.g., six-membered ring of SiO₄ tetrahedra). The high aftershock temperature at 20.7 GPa, which could be close to 800 °C, influenced the sample structure. However, some silanols, which were presumed to be the mutually hydrogen-bonded silanol group, remained at pressures >20.7 GPa. This type of silanol along with a small number of water molecules may remain even after shock compression at 30.9 GPa, although the intermediate structure of the sample recovered was similar to that of silica glass.