Geochemistry and petrology of howardite Miller Range 11100: A lithologically diverse piece of the Vestan regolith

The howardite‐eucrite‐diogenite (HED) clan of meteorites, which most likely originate from the asteroid Vesta, provide an opportunity to combine in‐depth sample analysis with the comprehensive remote‐sensing data set from NASA's recent Dawn mission. Miller Range (MIL) 11100, an Antarctic howardite, contains diverse rock and mineral fragments from common HED lithologies (diogenites, cumulate eucrites, and basaltic eucrites). It also contains a rare pyroxferroite‐bearing lithology—not recognized in HED until recently—and rare Mg‐rich (Fo_86‐91) olivine crystals that possibly represent material excavated from the Vestan mantle. Clast components underwent different histories of thermal and impact metamorphism before being incorporated into this sample, reflecting the diversity in geological histories experienced by different parts of Vesta. The bulk chemical composition and petrography of MIL 11100 suggest that it is akin to the fragmental howardite meteorites. The strong lithological heterogeneity across this sample suggests that at least some parts of the Vestan regolith show heterogeneity on the mm‐scale. We combine the outcomes of this study with data from NASA's Dawn mission and hypothesize on possible source regions for this meteorite on the surface of Vesta.     

Modeling orbital gamma‐ray spectroscopy experiments at carbonaceous asteroids

To evaluate the feasibility of measuring differences in bulk composition among carbonaceous meteorite parent bodies from an asteroid or comet orbiter, we present the results of a performance simulation of an orbital gamma‐ray spectroscopy (GRS) experiment in a Dawn‐like orbit around spherical model asteroids with a range of carbonaceous compositions. The orbital altitude was held equal to the asteroid radius for 4.5 months. Both the asteroid gamma‐ray spectrum and the spacecraft background flux were calculated using the MCNPX Monte‐Carlo code. GRS is sensitive to depths below the optical surface (to ≈20–50 cm depth depending on material density). This technique can therefore measure underlying compositions beneath a sulfur‐depleted (e.g., Nittler et al. 2001 ) or desiccated surface layer. We find that 3σ uncertainties of under 1 wt% are achievable for H, C, O, Si, S, Fe, and Cl for five carbonaceous meteorite compositions using the heritage Mars Odyssey GRS design in a spacecraft‐deck‐mounted configuration at the Odyssey end‐of‐mission energy resolution, FWHM = 5.7 keV at 1332 keV. The calculated compositional uncertainties are smaller than the compositional differences between carbonaceous chondrite subclasses.     

Bioremediation in Fractured Rock: 1. Modeling to Inform Design,Monitoring, and Expectations

Field characterization of a trichloroethene (TCE) source area in fractured mudstones produced a detailed understanding of the geology, contaminant distribution in fractures and the rock matrix, and hydraulic and transport properties. Groundwater flow and chemical transport modeling that synthesized the field characterization information proved critical for designing bioremediation of the source area. The planned bioremediation involved injecting emulsified vegetable oil and bacteria to enhance the naturally occurring biodegradation of TCE. The flow and transport modeling showed that injection will spread amendments widely over a zone of lower‐permeability fractures, with long residence times expected because of small velocities after injection and sorption of emulsified vegetable oil onto solids. Amendments transported out of this zone will be diluted by groundwater flux from other areas, limiting bioremediation effectiveness downgradient. At nearby pumping wells, further dilution is expected to make bioremediation effects undetectable in the pumped water. The results emphasize that in fracture‐dominated flow regimes, the extent of injected amendments cannot be conceptualized using simple homogeneous models of groundwater flow commonly adopted to design injections in unconsolidated porous media (e.g., radial diverging or dipole flow regimes). Instead, it is important to synthesize site characterization information using a groundwater flow model that includes discrete features representing high‐ and low‐permeability fractures. This type of model accounts for the highly heterogeneous hydraulic conductivity and groundwater fluxes in fractured‐rock aquifers, and facilitates designing injection strategies that target specific volumes of the aquifer and maximize the distribution of amendments over these volumes.     

Impacts of successive wildfire on soil hydraulic properties: Implications for debris flow hazards and system resilience

Climate and land use changes have led to recent increases in fire size, severity, and/or frequency in many different geographic regions and ecozones. Most post-wildfire geomorphology studies focus on the impact of a single wildfire but changing wildfire regimes underscore the need to quantify the effects of repeated disturbance by wildfire and the subsequent impacts on system resilience. Here, we examine the impact of two successive wildfires on soil hydraulic properties and debris flow hazards. The 2004 Nuttall-Gibson Complex and the 2017 Frye Fire affected large portions of the Pinaleño Mountains in southern Arizona, creating a mosaic of burn severity patterns that allowed us to quantify differences in wildfire-induced hydrologic changes as a function of burn severity and recent fire history (i.e. burned in only the Frye Fire or burned in both fires). Field observations after the 2017 Frye Fire indicated debris flow activity in areas burned predominantly at low severity. Many of these areas, however, were also affected by the 2004 Nuttall-Gibson Complex, suggesting that the relatively short recovery time between the two wildfires may have played a role in the geomorphic response to the most recent wildfire. Field measurements of soil hydraulic properties suggest that soils burned at moderate severity in 2004 and low severity in 2017 have a lower infiltration capacity relative to those that remained unburned in 2004 and burned at low severity in 2017. Simulations of runoff demonstrate that measured differences in infiltration capacity between once- and twice-burned soils are sufficient in some cases to influence the rainfall intensities needed to initiate runoff generated debris flows. Results quantify the impact of wildfire history and burn severity on runoff and debris flow activity in a landscape affected by successive wildfires and provide insight into how the resilience of geomorphic systems may be affected by successive wildfires. © 2019 John Wiley & Sons, Ltd.     

Properties of dust source material and volcanic ash in Iceland

The volcanic origin, primarily basaltic, of most of the surface material in Iceland influences its physical properties and appearance. Size distributions, shape analyses and melting experiments were made for surface material collected in high-erosion dust source areas and fresh volcanic ash deposits to determine whether they differ from one another and from dust from other major dust sources. The major differences found between Icelandic dust and dust from other major dust sources in the world, such as the Sahara, are in the particle shapes, lower density and darker colour. Icelandic dust particles greater than 20 μm retain volcanic morphological properties that are also found in fresh volcanic ash. Dust and fresh volcanic ash particles less than 20 μm are crystalline and blocky in nature, similar to the dust from other global source regions. The finer grained (<20 μm) Icelandic particles will have similar suspension and transport behaviours and be similarly hazardous to health and infrastructure as non-Icelandic dust. The coarser particles (>20 μm) will have different suspension and transport behaviours than other dusts due to the volcanic morphology. Icelandic surface material has between 5% and 30% glassy particles compared to fresh volcanic ash which has more than 50% glassy particles. Glassy particles were observed to melt at a lower temperature than the mineral grains; and, as a result, volcanic ash is found to be more threatening to aircraft engines than the typical dust from Iceland. Icelandic dust was observed to be blocky, or plate-like in the respirable size fraction, suggesting similar health hazards as dust from other regions.     

Geomorphology and ancient settlements of the Southern Flank of MT. Cairo,lower Liri valley,Italy

The southern flank of Mt. Cairo in southern Lazio edges a valley which forms one of the major passageways from central to southern Italy. The mountainous landscape has affected the settlement pattern, as have historical events such as the Roman conquests and recent socio-economic evolution, which has led to industrialization of a traditional pastoral- agricultural setting. The slopes of calcareous Mt. Cairo are characterized by a cascade of normal faults which delimit landscape units such as the “uplands,” “steep slopes,” and the “mountain rise,” which contains well developed alluvial and colluvial fans. Along the lower mountain slopes, Bronze and Iron Age sites are consistently located higher than Roman ones. Archaeological remains and historical documents indicate that only after the Roman conquest was the agricultural potential of the flatter lower areas fully exploited. Roman villas were characteristically placed on the upper parts of the fans, where both access to different types of land and elevation above the mists of the valley were enjoyed. The Medieval period brought a trend back to higher sites and fortified villages. The uplands remained in use through the ages.     

Records of aquatic pollen and sediment properties as indicators of late-Quaternary Alaskan lake levels

We investigated whether techniques developed to evaluate qualitative lake-level changes in the temperate zone can be used in sub-arctic and arctic Alaska. We focused on aquatic pollen records and sediment properties (loss-on-ignition and magnetic susceptibility) from centrally-located sediment-surface samples and cores, as these are the most commonly reported data in the literature. Modern aquatic pollen values are generally low (< 5%) and may be zero, even in lakes with abundant aquatic macrophytes. Greater diversity and higher values of aquatic pollen are likely at depths < 5 m, but pollen is found in depths up to 15 m. It is absent at depths > 20 m. Spores of Isoetes and Equisetum and Pediastrum cell-nets, when present, tend to be widely distributed, even in deep water. At Birch Lake, interior Alaska, trends in aquatic taxa and sediment characteristics for the last ca. 12,000 ¹⁴C yrs recorded in a single, deep-water core reflect the same water-level changes as do transect-based lake-level reconstructions - if modern distributional characteristics of pollen and spores are taken into account. The lake rose from extremely low levels at ca. 12,000 ¹⁴C yr B.P. After a period of fluctuation, it rose to a relatively high level by ca. 8000 ¹⁴C yr B.P. and then stabilized. A preliminary survey of aquatic pollen trends from other lake-sediment records suggests that the period ca. 11,000-8000 ¹⁴C yr B.P. may have seen relatively low lake levels in north-western and interior Alaska and high levels thereafter. Changes in aquatic pollen and sediments are evident in north-eastern interior lakes at the same time, but they are more difficult to interpret. Aquatic pollen productivity in Alaskan lakes may partly depend on factors other than water depth (e.g. temperature, pH, nutrient status, or length of the ice-free season). An Alaska-wide reconstruction of late-Quaternary lake levels based on extant single-core data would be best done after further study of contributing factors that may control sediment properties and aquatic pollen distribution.