Using beryllium-7 to evaluate soil erosion processes in agricultural lands in semiarid regions of Central Argentina

This work presents the results of a soil erosion study using the ⁷Be technique. This technique estimates the water erosion/deposition from the comparison between ⁷Be soil content of a reference site and an eroded or sedimented site. The soil samples were collected from an agricultural area of the semiarid region of Argentina near San Luis City, which has a marked rainfall season. The area has been used for crop cultivation, being subjected to plowing practices. The ⁷Be in the Reference Site was in the first centimeter of soil, showing the typical exponential decreasing of ⁷Be soil content with depth, with the ⁷Be inventories value being 340?±?50 Bq m^?2 for the dry season and 571?±?48 Bq m^?2 for the rainy season. The ⁷Be technique was applied to a potential eroded site subjected to traditional tillage practices (plowing). A net soil erosion value of 13.5 t ha^?1 (1.35 kg m^?2) was obtained. From the assumptions of the applied technique, we can draw the inference that this erosion was caused by rains produced in the month prior to the date of soil sampling.     

Global and regional ridge patterns on Mars

Over 16,000 wrinkle ridges on Mars have been classified, mapped, and digitized to provide a large computer-accessible data base for analyzing regions subjected to possible compressive stresses. The survey has revealed major compressive structures that occur well beyond the Tharsis-dominated hemisphere. The large variety of affected geologic terrains indicate stresses not simply localized in the intercrater plains. One major area of inferred compression occurs in the southern cratered highlands near longitude 180°W where major ridges and scarps extend over 3000 km. The occurrence and orientation of many ridges are locally controlled by ancient impact basins. The Chryse basin in particular has an important effect on ridges in northern Lunae Planum. The removal of all basin-concentric ridges reveals, however, a complex global pattern. Although such patterns may yet be controlled by heavily degraded impact basins, major regional trends also emerge that appear to require broader scale global stresses. Most ridges in the Western Hemisphere are shown to be orthogonal to three centers corresponding to Tharsis (1°N, 122°W), Syria (12°S, 104°W), and Chryse (19°N, 47°W). Ridges not included in these three sets are generally more random and highly localized. Most, but by no means all, ridges in the Eastern Hemisphere are controlled by the Hellas and Isidis basins. A simple global grid is not yet identifiable and may not be recognizable owing to the large number of regional patterns.     

A multi-wavelength study of the 2009 impact on Jupiter: Comparison of high resolution images from Gemini,Keck and HST

Within several days of A. Wesley’s announcement that Jupiter was hit by an object on UT 19 July 2009, we observed the impact site with (1) the Hubble Space Telescope (HST) at UV through visible (225–924 nm) wavelengths, (2) the 10-m W.M. Keck II telescope in the near-infrared (1–5 μm), and (3) the 8-m Gemini-North telescope in the mid-infrared (7.7–18 μm). All observations reported here were obtained between 22 and 25 July 2009. Observations at visible and near-infrared wavelengths show that large (～0.75-μm radius) dark (imaginary index of refraction m_i ～ 0.01–0.1) particulates were deposited at atmospheric pressures between 10 and 200–300 mbar; analysis of HST-UV data reveals that in addition smaller-sized (～0.1 μm radius) material must have been deposited at the highest altitudes (～10 mbar). Differences in morphology between the UV and visible/near-IR images suggest three-dimensional variations in particle size and density across the impact site, which probably were induced during the explosion and associated events. At mid-infrared wavelengths the brightness temperature increased due to both an enhancement in the stratospheric NH₃ gas abundance and the physical temperature of the atmosphere. This high brightness temperature coincides with the center part of the impact site as seen with HST. This observation, combined with (published) numerical simulations of the Shoemaker-Levy 9 impacts on Jupiter and the Tunguska airburst on Earth, suggests that the downward jet from the terminal explosion probably penetrated down to the ～700-mbar level.     

Amplified hazard of small-volume monogenetic eruptions due to environmental controls, Orakei Basin, Auckland Volcanic Field, New Zealand

Orakei maar and tuff ring in the Auckland Volcanic Field is an example of a basaltic volcano in which the style and impacts of the eruption of a small volume of magma were modulated by a fine balance between magma flux and groundwater availability. These conditions were optimised by the pre-85?ka eruption being hosted in a zone of fractured and variably permeable Plio-Pleistocene mudstones and sandstones. Orakei maar represents an end-member in the spectrum of short-lived basaltic volcanoes, where substrate conditions rather than the magmatic volatile content was the dominant factor controlling explosivity and eruption styles. The eruption excavated a crater ?80?m deep that was subsequently filled by slumped crater wall material, followed by lacustrine and marine sediments. The explosion crater may have been less than 800?m in diameter, but wall collapse and wave erosion has left a 1,000-m-diameter roughly circular basin. A tuff ring around part of the maar comprises dominantly base surge deposits, along with subordinate fall units. Grain size, texture and shape characteristics indicate a strong influence of magma–water and magma–mud interactions that controlled explosivity throughout the eruption, but also an ongoing secondary role of magmatic gas-driven expansion and fragmentation. The tuff contains >70?% of material recycled from the underlying Plio-Pliestocene sediments, which is strongly predominant in the >2 ? fraction. The magmatic clasts are evolved alkali basalt, consistent with the eruption of a very small batch of magma. The environmental impact of this eruption was disproportionally large, when considering the low volume of magma involved (DRE?<?0.003?km³). Hence, this eruption exemplifies one of the worst-case scenarios for an eruption within the densely populated Auckland City, destroying an area of ~3?km² by crater formation and base surge impact. An equivalent scenario for the same magma conditions without groundwater interaction would yield a scoria/spatter cone with a diameter of 400–550?m, destroying less than a tenth of the area affected by the Orakei event.     

Assessing Carbon Stock and Sequestration of the Tropical Seagrass Meadows in Indonesia

Ocean Science Journal - Seagrass meadows provide critical ecosystem services for coastal areas, e.g., as nursery habitats for various fish species, help with water filtration of suspended sediment,...