Spatial and temporal variability of soil water content in two regions of Southwest German

Soil water content (SWC) plays a key role in partitioning of energy and water fluxes on the land surface. Knowledge about spatial and temporal variability of topsoil water content is crucial for understanding land surface processes, improving climate and hydrology modeling. In recent study, we investigated SWC variability, its relation to the mean spatial soil water content (qm) and variability of rainfall on the regional spatial and event temporal scales. To accomplish this, we used a multi-year high resolution data set, obtained from two soil moisture sensor networks (spatial extent of 25 km ×25 km), set up at croplands in Kraichgau and Swabian Alb regions in Southwest Germany. The relationship of SWC standard deviation (sq) versus áqñ was studied (sq-qm). It was found that the initial location of sq in relation to the sq at the permanent wilting point (sq-qwp) and the sq at saturation (sq-qs) – the anchor points – as well as the upper and lower bounds of the sq-qm envelope determine whether SWC variability increases or decreases upon a change in qm. sq-qm relationship forms combinations of concave and convex hyperbolas reflecting the variability of soil texture and depending on sq in relation to the anchor points. The majority of sq-qm clockwise hysteresis cases were observed in intermediate and intermediate/wet state of SWC. The sq phase-space can be used to test whether hydrological or land surface models capture the reasonable range of soil water heterogeneity

Picture Gorge Basalt: Internal stratigraphy, eruptive patterns, and its importance for understanding Columbia River Basalt Group magmatism

The Picture Gorge Basalt (PGB) of the Columbia River Basalt Group (CRBG) has been previously thought to be limited in its eruptive volume (\u3c3000 \u3ekm3) and thought to not extend far from its type locality. At present, PGB represents only 1.1 vol% of the CRBG with a relatively limited spatial distribution of ~10,000 km2. New age data illustrate that the PGB is the earliest and longest eruptive unit compared to other main-phase CRBG formations and that some dated basaltic flows reach far (~100 km) beyond the previously mapped extent. This study focuses on extensive outcrops of basaltic lavas and dikes south of the type locality at Picture Gorge, in order to reassess the spatial distribution and eruptive volume of the PGB. Field observations coupled with geochemical data indicate that PGB lava flows and mafic dikes covered a significantly greater area than shown on the published geologic maps. We find that additional mafic dikes located farther south of the original mapped distribution have geochemical compositions and northwest-trending orientations comparable to the dikes of the Monument dike swarm. We also identify new lava flows that can be correlated where stratigraphic control is well defined toward the original mapped PGB distribution. Our analyses and correlations are facilitated by comparison of 20 major- and trace-element abundances via a principal component analysis. This statistical comparison provides a new detailed distribution of PGB with stratigraphic significance that more than doubles the total distribution of PGB lavas and dikes and brings the eruptive volume to a new minimum of at least ~4200 km3. Geochemically correlated basaltic lavas and dikes in the extended distribution of PGB represent the earlier and later sections of the internal PGB stratigraphy. This is an intriguing observation as new geochronological data suggest an eruptive hiatus of ~400 k.y. during PGB volcanic activity, which occurred from 17.23 Ma to 15.76 Ma. The geochemical identifiers used to differentiate PGB from other main-phase CRBG formations include lower TiO2 (\u3c2 \u3ewt%) concentrations, lower incompatible trace-element (i.e., La, Th, and Y) abundances, and a more pronounced enrichment in large- ion- lithophile elements (LILEs) on a primitive mantle–normalized trace-element diagram (Sun and McDonough, 1989). Geochemical characteristics of PGB are interpreted to represent a magmatic source component distinct from the other main-phase CRBG units, possibly a localized backarc-sourced mantle melt. However, this source cannot be spatially restricted as there are observed PGB lava flows and dikes extending as far east as Lake Owyhee and as far south as Hart Mountain, covering at least 15,000 km2. In context with the existing stratigraphy and the new extent of PGB lavas and dikes, these ages and coupled geochemical signatures demonstrate this mantle component was not spatially localized but rather tapped across a wide region

Incarnation of Pompilia

Englis

Volcanology and petrology of the Rattlesnake Ash-Flow Tuff, eastern Oregon

The Rattlesnake Ash-Flow Tuff erupted 7.05±0.01 Ma from the western Harney Basin, southeastern Oregon. The location of the vent area is inferred based on vent-ward increases in size of pumices, in degree of welding, and in degree of post-emplacement crystallization. Today's outcrops cover 9000 km2 and estimated original outcrop coverage was ca. 35000 km2. Tuff thickness is uniform ranging mainly between 5 and 30 in with maxima up to 70 in. Estimated eruption volume is 280 km3 dense rock equivalent (DRE). Lithological variations include vitric non- to densely welded tuff, vapor-phase, devitrified, spherulitic, lithophysal, and rheomorphic tuff. Lithological zoning characteristics of the tuff change locally at nearly constant tuff thickness over distances of 1 to 3 km grading from incipiently welded tuff to highly zoned sections. Regional variations become apparent by integrating many sections from one area. A three-dimensional facies model is developed describing the local and regional facies variations. The Rattlesnake Tuff consists of high-silica rhyolite (HSR) erupted as pumices and glass shards. Dacite pumices make up less than 1% of the total volume and quenched basalt and basaltic andesite inclusions inside dacite pumices constitute << 0.1 volume %. HSR pumices cluster in 4 to 5 compositional groups which are discerned best by La, Eu, Ba, Hf(Zr), Ta(Nb). Major element variations are minor but consistent between groups with Si02 increasing and FeO*, MgO, Ti02, and CaO decreasing with differentiation. Modal mineralogy, mineral chemistry, and partition coefficients also change progressively. The diversity of HSR is likely the product of crystal fractionation processes. A model is proposed by which a stratified magma chamber is generated from the roof of the chamber downward by progressively more evolved HSR. Least evolved HSR is likely the product of dehydration melting of high-grade intermediate to mafic protoliths. High Ba/Rb ratios of 30 in the least evolved HSR limit the potential protoliths to lithologies with equal or higher Ba/Rb. Dacite pumices and mafic inclusions reveal the nature of the mafic root zone to the Rattlesnake Tuff magma chamber. Quenching and mingling textures with the host pumice indicate that basaltic andesite and basalt inclusions are cognate. Dacite formed at the interface between HSR and underlying enriched basaltic andesite and was generated by mixing of these two components. Basaltic andesite is fractionated and enriched in trace elements compared to regional primitive tholeiite (HAOT). Basaltic andesite has evolved from HAOT's mainly through fractionation and recharge while being stalled underneath a silicic cap

Filling Critical Gaps in the Space-Time Record of High Lava Plains and co-Columbia River Basalt Group rhyolite Volcanism

Miocene rhyolitic volcanism of eastern Oregon, USA, can be divided into two main episodes. Mantle plume upwelling is thought to have generated Columbia River Basalt Group (CRBG) lavas and coeval \u3e16.5−15 Ma silicic volcanism trending north−south from northeast Oregon to northern Nevada. Rhyolite volcanism of the 12−0 Ma High Lava Plains province has been ascribed to either buoyancy-driven westward plume spreading or to slab rollback and mantle convection spanning from southeast Oregon to Newberry Volcano to the west. The apparent ca. 15−12 Ma eruptive hiatus suggests that rhyolites of these provinces were a product of separate processes, yet this gap was based on incomplete data. The lack of data on ∼33 of the total ∼50 rhyolitic eruptive centers in the area where the two provinces overlap (117−119°W, 43−44°N) yields only tenuous relationships between these two provinces

Columbia River Rhyolites: Age-Distribution Patterns and Their Implications for Arrival, Location, and Dispersion of Continental Flood Basalt Magmas in the Crust

Columbia River province magmatism is now known to include abundant and widespread rhyolite centers even though the view that the earliest rhyolites erupted from the McDermitt Caldera and other nearby volcanic fields along the Oregon–Nevada state border has persisted. Our study covers little-studied or unknown rhyolite occurrences in eastern Oregon that show a much wider distribution of older centers. With our new data on distribution of rhyolite centers and ages along with literature data, we consider rhyolites spanning from 17.5 to 14.5 Ma of eastern Oregon, northern Nevada, and western Idaho to be a direct response to flood basalts of the Columbia River Basalt Group (CRBG) and collectively categorize them as Columbia River Rhyolites. The age distribution patterns of Columbia River Rhyolites have implications for the arrival, location, and dispersion of flood basalt magmas in the crust. We consider the period from 17.5 to 16.4 Ma to be the waxing phase of rhyolite activity and the period from 15.3 to 14.5 Ma to be the waning phase. The largest number of centers was active between 16.3–15.4 Ma. The existence of crustal CRBG magma reservoirs beneath rhyolites seems inevitable, and hence, rhyolites suggest the following. The locations of centers of the waxing phase imply the arrival of CRBG magmas across the distribution area of rhyolites and are thought to correspond to the thermal pulses of arriving Picture Gorge Basalt and Picture-Gorge-Basalt-like magmas of the Imnaha Basalt in the north and to those of Steens Basalt magmas in the south. The earlier main rhyolite activity phase corresponds with Grande Ronde Basalt and evolved Picture Gorge Basalt and Steens Basalt. The later main phase rhyolite activity slightly postdated these basalts but is contemporaneous with icelanditic magmas that evolved from flood basalts. Similarly, centers of the waning phase span the area distribution of earlier phases and are similarly contemporaneous with icelanditic magmas and with other local basalts. These data have a number of implications for long-held notions about flood basalt migration through time and the age-progressive Snake River Plain Yellowstone rhyolite trend. There is no age progression in rhyolite activity from south-to-north, and this places doubt on the postulated south-to-north progression in basalt activity, at least for main-phase CRBG lavas. Furthermore, we suggest that age-progressive rhyolite activity of the Snake River Plain–Yellowstone trend starts at ~12 Ma with activity at the Bruneau Jarbidge center, and early centers along the Oregon–Nevada border, such as McDermitt, belong to the early to main phase rhyolites identified here

Angular sensitivity of blowfly photoreceptors: intracellular measurements and wave-optical predictions

The angular sensitivity of blowfly photoreceptors was measured in detail at wavelengths λ = 355, 494 and 588 nm. The measured curves often showed numerous sidebands, indicating the importance of diffraction by the facet lens. The shape of the angular sensitivity profile is dependent on wavelength. The main peak of the angular sensitivities at the shorter wavelengths was flattened. This phenomenon as well as the overall shape of the main peak can be quantitatively described by a wave-optical theory using realistic values for the optical parameters of the lens-photoreceptor system. At a constant response level of 6 mV (almost dark adapted), the visual acuity of the peripheral cells R1-6 is at longer wavelengths mainly diffraction limited, while at shorter wavelengths the visual acuity is limited by the waveguide properties of the rhabdomere. Closure of the pupil narrows the angular sensitivity profile at the shorter wavelengths. This effect can be fully described by assuming that the intracellular pupil progressively absorbs light from the higher order modes. In light-adapted cells R1-6 the visual acuity is mainly diffraction limited at all wavelengths.