The role of basalt replenishment in the generation of basaltic andesites of the ongoing activity at Arenal volcano,Costa Rica: evidence from clinopyroxene and spinel

Bulletin of Volcanology - The bulk composition of magma erupted from Volcán Arenal has remained nearly constant (SiO2 = 53.6–54.9&;nbsp;wt%; MgO = 5.0–4.5&;nbsp;wt%) during...     

Solar Eclipses and the Surface Properties of Water

Earth, Moon, and Planets - During four solar eclipse events (two annular, one total and one partial) a correlation was observed between a change in water surface tension and the magnitude of the...     

Reconstruction and Regional Significance of the Coire Breac Palaeoglacier,Glen Esk,Eastern Grampian Highlands,Scotland

We present a glaciological and climatic reconstruction of a former glacier in Coire Breac, an isolated cirque within the Eastern Grampian plateau of Scotland, 5 km from the Highland edge. Published glacier reconstructions of presumed Younger Dryas‐age glaciers in this area show that equilibrium line altitudes decreased steeply towards the east coast, implying a arctic maritime glacial environment. Extrapolation of the ELA trend surface implies that glaciers should have existed in suitable locations on the plateau, a landscape little modified by glaciation. In Coire Breac, a 0.35 km² cirque glacier existed with an equilibrium line altitude of 487 ± 15 m above present sea level. The equilibrium line altitude matches closely the extrapolated regional equilibrium line altitude trend surface for Younger Dryas Stadial glaciers. The mean glacier thickness of 24 m gives an ice volume of 7.8 × 10⁶ m³, and a maximum basal shear stress of c. 100 kPa^?1. Ablation gradient was c. –0.0055 m m^?1, with a mean July temperature at the equilibrium line altitude of c. 5.1°C. The reconstruction implies an arctic maritime climate of low precipitation with local accumulation enhanced by blown snow, which may explain the absence of other contemporary glaciers nearby. Reconstructed ice flow lines show zones of flow concentration around the lower ice margin which help to explain the distribution of depositional facies associated with a former debris cover which may have delayed eventual glacier retreat. No moraines in the area have been dated, so palaeoclimatic interpretations remain provisional, and a pre‐Lateglacial Interstadial age cannot be ruled out.     

Spinel compositional variation in the crustal and mantle lithologies of the Othris ophiolite

Spinels from cumulus and non-cumulus members of the Othris ophiolite display a considerable variation in composition. Cumulus picrites and gabbros contain either a primary chromite and/or a reaction spinel formed by reaction with co-existing silicates (Cr-Al varia tion) or intercumulus liquid (Cr-Fe variation). Non-cumulus peridotites contain spinels which vary along a Cr-Al trend. Harzburgites contain a Cr-spinel and lherzolites a more aluminous spinel. The occurence of gabbroic segregations within the host lherzolite appears to affect the spinel chemistry. Spinels adjacent to these plagioclase—diopside veinlets are richer in aluminium than the spinels scattered within the depleted lherzolite surrounding the veinlet. [Protoclastic harzburgites contain a highly aluminous spinel phase either as an exsolution phase within pyroxenes or as a groundmass spinel.] The Cr-Al variation of the peridotites is believed to have resulted from interaction with interstitial aluminous liquid—in situ basaltic melt from a fused peridotite?     

Moisture characteristics and their point pedotransfer functions for coarse‐textured tropical soils differing in structural degradation status

The effect of soil structure on hydraulic pedotransfer functions (PTFs) in tropical soils with similar mineralogy and texture has not been well documented. Structurally contrasting soils from representative locations in southeastern Nigeria were analyzed for moisture retention at 0, 6, 10, 33, 100, 300 and 1500 kPa among other properties. They were grouped by depth (topsoils or subsoils) and also by their structural degradation status into low‐ and high‐stability soils, corresponding to organic matter (OM):[silt + clay] of <7.5 and >7.5%, respectively. Soil depth and structural stability influenced the soil moisture characteristic curves. The data were fitted to three tropical point PTFs, but none of them proved appropriate for predicting moisture retention in the soils. We therefore derived new ones using multiple linear stepwise regressions before and after the dataset grouping and compared their performances by means of cross‐validation. Moisture retention in the soils (sand content, 73.2–93.8%) could not be calibrated from texture and OM concentration alone, until when bulk density, total porosity and microporosity were included among the regressors. Microporosity's role was particularly outstanding at all matric potentials but the 1500 kPa. The ensuing PTFs represent a good fit for the soil moisture retention data. The two grouping strategies resulted in lower SE of the estimates in some cases, but this did not enhance the performances of the concerned PTFs. At the 1500 kPa, however, the PTF incorporating all datasets performed better than separate PTFs for topsoils/subsoils but worse than the one for high‐stability soils. Information on soil structure can therefore benefit PTF derivation for kaolinite‐dominated, coarse‐textured tropical soils at all the matric potentials considered. Copyright © 2012 John Wiley & Sons, Ltd.