The 18-km-diameter El'gygytgyn crater is located on the Chukotka peninsula, northeastern Russia. It represents the only currently known impact structure formed in siliceous volcanics, including tuffs. The impact melt rocks and target rocks provide an excellent opportunity to study shock metamorphism of volcanic rocks. The shockinduced changes observed in porphyritic volcanic rocks from El'gygytgyn can be applied to a general classifi cation of shock metamorphism of siliceous volcanic rocks. Strongly shocked volcanic rocks with phenocrysts converted to diaplectic quartz glass and partially melted feldspars as well as cryptocrystalline matrices are widespread in the El'gygytgyn crater. In particular, the following different stages of shock metamorphism are observed: (i) weakly to moderately shocked lavas and tuffs with phenocrysts and clasts of quartz and feldspars; (ii) moderately shocked volcanic rocks and tuffs with diaplectic glasses of quartz and feldspars; (iii) strongly shocked lavas and tuffs with phenocrysts of diaplectic quartz glass and fused glasses of feldspars in melted matrixes; and (iv) impact melt rocks and impact glasses. In addition, thin glassy coatings of voids in impact melt rocks have been observed. While the shock-induced changes of clasts of framework silicates in these volcanic rocks do not differ from respective changes in other crystalline rocks, the fi negrained matrix of porphyritic rocks is converted into fused glass at the same shock pressures as feldspar minerals. No remnants of fi ne-grained quartz are preserved in matrix converted into fused glass by shock.

This paper examines whether eastern Tigray is still in a phase of land degradation or if a trend of landscape greening has started. Hitherto, the land cover in five representative Tigray villages was mapped for three different periods: 1965, 1994, and 2007. These maps were based on the interpretation of aerial photographs and high‐resolution satellite imagery in combination with field validation. The results show a strong decrease of the forest and bush land in favor of arable land and rangeland from 1965 to 1994. This trend is, however, slowed down and even reversed from 1994 onwards whereby some of the arable land and rangeland are abandoned allowing shrubs and bushes to regenerate. Household interviews and census data showed that the rural population number is still increasing. However, the productivity of the farming activities did not show a significant increase. The observed abandonment of marginal farm and rangeland is, therefore, made possible only through food aid and the import of food from other regions. Furthermore, policymakers stimulate land abandonment and landscape greening by establishing exclosures. Copyright © 2014 John Wiley & Sons, Ltd.

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Water availability has for long been a critical issue in many developing countries. Despite its enormous potential of water resources, Ethiopia is suffering from a lack of water availability and threatened by the consequences of climate change. Well considered planning to develop these resources is crucial. However, very few observational runoff data exist for this type of environments. Especially runoff data for catchments at the intermediate scale (100 -10,000 km²) are lacking. This study assesses the runoff from 10 mediumsized catchments in the Geba river basin, a subcatchment of the Nile in the semi-arid degraded northern Ethiopian highlands. Flow depth records were automatically obtained every 10 minutes during the rainy seasons (July -September) of 2004-2007 and converted to continuous runoff discharge records.Cumulative annual runoff depths (46 -395 mm) are mainly correlated with rainfall depth. Estimated runoff coefficients (9 -47%) and are negatively correlated with the areal fraction of limestone outcrops in the catchments, indicating runoff transmission losses.Throughout the rainy season, increases in runoff depth and runoff coefficient were observed, which is partly attributed to an increase in baseflow throughout the season. The majority of the runoff occurs during flash floods, i.e. relatively short runoff events with often very high peak discharges. Characteristics of these floods 2 are discussed with some examples, including an exceptionally large flood. Taking into account the difficult conditions for river discharge measurements in a country like Ethiopia, this study provides one of the most comprehensive analyses so far of the magnitude and dynamics of river discharges in Ethiopia.

The ferricrete deposit in Adi Kokeb district was investigated using field observations, petrographic studies and chemical analysis of samples for their geochemistry and mode of origin. Field observations confirmed the presence of kaolinites, thin iron bands and relict quartz veins. Petrographic studies of the samples revealed that quartz, sericite, muscovite, orthoclase feldspar and iron oxides/hydroxides are the dominant minerals. Geochemical determination of major, minor and trace elements of seventeen (17) samples were done using X-ray fluorescence (XRF). The results show a general increasing trend in Fe 2 O 3 (16.75-57.9 wt.%) and Al 2 O 3 (11.35-16.44 wt.%) values and decreasing trends in SiO 2 (57.05-22.01 wt.%) values from the Meta-sandstone to the ferricrete. The alkali and alkaline earth elements, notably K 2 O (0.142 wt.%), Na 2 O (<0.005 wt.%), CaO (0.075 wt.%) and MgO (0.098 wt.%), are highly depleted, confirming that iron precipitation with subsequent oxidation is major process in ferricrete formation. Similarly, the minor elements such as MnO (0.17 wt.%), TiO 2 (0.56 wt.%) and P 2 O 5 (0.154 wt.%) are highly depleted, implying their weak substitution for major elements in the ferricrete. The average value of trace elements such as Ba (669 ppm), Zr (348 ppm), Sr (215 ppm), Cu (125 ppm), Zn (55 ppm) and Pb (9.5 ppm) show a relative enrichment of the ferricrete compared to ferruginous sandstone and metasandstone. The relatively high concentrations of Zr, Ba and Sr in the ferricrete are attributed to their presence in detrital material during weathering (Zr) and their adsorption on neoformed kaolinite (Ba and Sr). Integration of field, petrographic and geochemical results suggest that the origin of this deposit is associated with weathering processes. Therefore, the deposit is likely to be a ferricrete.