The 2011 eruption of Nabro volcano,Eritrea: perspectives on magmatic processes from melt inclusions     

Amy?DonovanEmail authorView author&#;s OrcID profile  Jon?Blundy  Clive?Oppenheimer  Iris?Buisman 《Contributions to Mineralogy and Petrology》2018,173(1):1

The 2011 eruption of Nabro volcano, Eritrea, produced one of the largest volcanic sulphur inputs to the atmosphere since the 1991 eruption of Mt. Pinatubo, yet has received comparatively little scientific attention. Nabro forms part of an off-axis alignment, broadly perpendicular to the Afar Rift, and has a history of large-magnitude explosive silicic eruptions, as well as smaller more mafic ones. Here, we present and analyse extensive petrological data obtained from samples of trachybasaltic tephra erupted during the 2011 eruption to assess the pre-eruptive magma storage system and explain the large sulphur emission. We show that the eruption involved two texturally distinct batches of magma, one of which was more primitive and richer in sulphur than the other, which was higher in water (up to 2.5 wt%). Modelling of the degassing and crystallisation histories demonstrates that the more primitive magma rose rapidly from depth and experienced degassing crystallisation, while the other experienced isobaric cooling in the crust at around 5 km depth. Interaction between the two batches occurred shortly before the eruption. The eruption itself was likely triggered by recharge-induced destabilisation of vertically extensive mush zone under the volcano. This could potentially account for the large volume of sulphur released. Some of the melt inclusions are volatile undersaturated, and suggest that the original water content of the magma was around 1.3 wt%, which is relatively high for an intraplate setting, but consistent with seismic studies of the Afar plume. This eruption was smaller than some geological eruptions at Nabro, but provides important insights into the plumbing systems and dynamics of off-axis volcanoes in Afar.  相似文献   

Kilofarms in The Agricultural Heartland     

John Fraser Hart  Mark B. Lindberg 《Geographical review》2014,104(2):139-152

Kilofarms are farms of 1,000 acres or more. The U.S. Department of Agriculture's Census of Agriculture has few tabulations of data by farm size, but geographical analysis suggests some of the characteristics of kilofarms. Their operators are part‐owner farmers. Their land and buildings are worth several millions of dollars, and their gross annual income is well over the $250,000 necessary to provide an acceptable level of living for a contemporary farm family. Kilofarmers concentrate on growing crops of corn and soybeans for cash sale, and they rely on computers and Internet access to help them make marketing decisions.  相似文献   

Limnology of Lake Waikaremoana with special reference to littoral and pelagic primary producers     

Clive Howard‐Williams  Karen Law  Connie L. Vincent  John Davies  Warwick F. Vincent 《新西兰海洋与淡水研究杂志》2013,47(4):583-597

Lake Waikaremoana, the North Island's deepest lake (248 m), lies in a natural forested catchment, but the lake itself has been modified for hydro‐electric power generation and by the introduction of trout, smelt, and adventive aquatic plants. The lake is a warm monomictic water body of low conductivity (82 μS cm^‐1) and a high seasonal water column stability. The waters are oligotrophic, with epilimnetic dissolved reactive phosphorus concentrations typically < 1 mg m^‐3. The concentration of NO₃‐N is seasonally variable but generally high in winter and spring with maximum epilimnetic values approaching 70 mg m ³. This contrasts with other central North Island lakes. Horizontal variability in surface chlorophyll a is low as are the absolute values (< 1–2 mg m^‐3). A notable feature is the formation of a deep chlorophyll maximum within the metalim‐nion comprised largely of Sphaewcystis schweteri as opposed to diatoms and flagellates which normally dominate the epilimnion. Vascular macro‐phytes (maximum biomass 659 g m² dry weight) extended to 9 m and characeans (maximum biomass 447 g m²dry weight) to 16 m. Total phyto‐plankton primary production was calculated as 4524 tCy^‐1 and macrophyte production as 578 t C y^‐1. The proportion of macrophyte to phy‐toplankton production (0.14) is higher than in the other deep lakes of the central North Island.  相似文献   

Scheduling for Robonet‐1 homogenous telescope network     

S. N. Fraser 《Astronomische Nachrichten》2006,327(8):779-782

The Robonet‐1 homogenous telescope network consists of 3 fully robotic 2 m class telescopes. I describe how the observation requests submitted by external users and automated user agents are selected for observation by the individual telescope schedulers. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Rough quarries,rocks and hills: John Pull and the Neolithic flint mines of Sussex     

Clive Waddington 《Geoarchaeology》2003,18(2):285-286

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