Siting criteria for heat extraction from hot dry rock; Application to Switzerland

For selecting possible hot dry rock extraction sites for geothermal energy applications, the following criteria have been considered: (i) depth to the crystalline basement, (ii) temperatures at depth, (iii) pattern of regional stress field and (iv) natural permeability (=degree of fracturing) of basement rocks. A contour map of the basement topography is presented. From outcrops at the nothern border of Switzerland (crystalline rocks of the Black Forest massif, mainly granites and gneisses of Hercynian age) the basement dips gently toward the SE under the Mesozoic and Tertiary sediments of the Molasse Basin and reaches its maximum depth (7 km) underneath the front of the Alps. Some 30 km further SE the basement rocks appear at the surface (Aar- and Gotthard-massif, Penninic units), where they are deformed and fractured to a great extent. Temperature-depth profiles have been obtained by model calculations. Locally increased heat product on (in granite batholiths) at the base of the Molasse Basin, combined with the blanketing effect of the overlying sediments, could raise the temperatures to 150–170°C at a depth of 5 km. According to earthquake fault-plane solutions (P-axes) the regional stress field in the area of the Swiss Alps and in its northern Foreland is characterized by the maximum horizontal compression oriented N(150±20)°E in the upper crust.In situ stress determinations (overcoring experiments) show that considerable excess horizontal compressive stress is present in the Alpine crust (up to 200 bar). The deep Alpine tunnels exhibited considerable fracturing of crystalline rocks at depths greater than 1–2 km. Information about the degree of fracturing has also been obtained by refraction profiles. The velocitydepth functions show lower than normal velocities in the uppermost 1.5 km, indicating that the rocks there are fractured. A 30–40 km wide region, running along the axis of the Molasse Basin (which coincides with the majority of the population and most of the industry of Switzerland) would provide the best hot dry rock sites.Paper presented at the Second NATO-CCMS Meeting on Dry Hot Rock Geothermal Energy, 28–30 June 1977, Los Alamos, New Mexico, USA. Contribution No. 198, Institute of Geophysics ETH Zurich.     

“Galileo Galilei” (GG) a small satellite to test the equivalence principle of Galileo, Newton and Einstein

“Galileo Galilei” (GG) is a small satellite designed to fly in low Earth orbit with the goal of testing the Equivalence Principle—which is at the basis of the General Theory of Relativity—to 1 part in 10¹⁷. If successful, it would improve current laboratory results by 4 orders of magnitude. A confirmation would strongly constrain theories; proof of violation is believed to lead to a scientific revolution. The experiment design allows it to be carried out at ambient temperature inside a small 1-axis stabilized satellite (250 kg total mass). GG is under investigation at Phase A-2 level by ASI (Agenzia Spaziale Italiana) at Thales Alenia Space in Torino, while a laboratory prototype (known as GGG) is operational at INFN laboratories in Pisa, supported by INFN (Istituto Nazionale di fisica Nucleare) and ASI. A final study report will be published in 2009.     

Kinetics of CO2 production on venus

Consideration of theoretical limits and experimental data for the kinetics of the reaction quartz + calcite → wollastonite + CO₂ supports the concept of a shortterm quasiequilibrium state for the atmosphere of Venus. These data indicate that the time scale of this reaction and of any competing CO₂ producing reaction may be as short as several hundred years or less at the inferred Venus surface temperatures.     

北部湾东北部2000年以来高分辨率粘土矿物记录及古环境意义

北部湾东北部 GC19-28 孔260BC~1480A.D. 粘土矿物学的高分辨率（平均分辨率为15年）分析表明,该孔的粘土矿物主要由蒙脱石（50%~61%）组成,含中等含量的伊利石（13%~18%）、高岭石（13%~18%）和绿泥石（11%~16%）,在该时间序列上蒙脱石与其他3种粘土矿物变化趋势基本相反。物源区分析显示,GC19-28 孔粘土矿物中的蒙脱石主要由红河提供,伊利石、高岭石和绿泥石主要来源于珠江。该孔高岭石/蒙脱石比值可以反映华南珠江流域季风降雨变化,比值增加表明珠江流域降雨增强;反之亦然。研究结果发现,GC19-28 孔的4种粘土矿物整体表现2个阶段性变化：1）260BC~1200A.D.,4种粘土矿物的相对含量基本保持不变,高岭石/蒙脱石比值同样保持不变;2）从 1200~1480A.D.,蒙脱石相对含量逐渐降低,伊利石、高岭石和绿泥石相对含量逐渐增加,高岭石/蒙脱石比值开始增加。结合贵州董哥洞石笋、广东湖光岩、西沙东岛湖泊沉积物和西太平洋暖池区海表古温度等高分辨率地质记录,推断华南珠江流域由中世纪暖期向小冰期转换过程中,降雨逐渐增加。     

Flow localization in fissure eruptions

 During a basaltic fissure eruption heat transfer from the hot magma to the surrounding rock causes a dramatic increase in the magmatic viscosity and solidification at the margins. Both viscosity contrast and solidification can amplify initial variations in the flow rate and lead to localization of the flow along the strike of the fissure. However, for typical parameters, amplification driven by solidification is slower and significantly weaker than amplification driven by viscosity variations. In fact, for the parameters examined, the amplification due to solidification is so weak that its effect is almost insignificant, whereas viscosity variation provides a strong active mechanism for flow localization. Laboratory experiments illustrate viscous localization and suggest that this mechanism is robust. The dependence of viscosity on temperature can cause a small change in the pressure of the magma chamber to lead to a large jump in the flow rate of magma through the fissure. Received: 13 March 1998 / Accepted: 27 September 1998     

The 1991 eruption of Hekla,Iceland

The eruption that started in the Hekla volcano in South Iceland on 17 January 1991, and came to an end on 11 March, produced mainly andesitic lava. This lava covers 23 km² and has an estimated volume of 0.15 km³. This is the third eruption in only 20 years, whereas the average repose period since 1104 is 55 years. Earthquakes, as well as a strain pulse recorded by borehole strainmeters, occurred less than half an hour before the start of the eruption. The initial plinian phase was very short-lived, producing a total of only 0.02 km³ of tephra. The eruption cloud attained 11.5 km in height in only 10 min, but it became detached from the volcano a few hours later. Several fissures were active during the first day of the eruption, including a part of the summit fissure. By the second day, however, the activity was already essentially limited to that segment of the principal fissure where the main crater subsequently formed. The average effusion rate during the first two days of the eruption was about 800 m³ s^–1. After this peak, the effusion rate declined rapidly to 10–20 m³ s^–1, then more slowly to 1 m³ s^–1, and remained at 1–12 m³ s^–1 until the end of the eruption. Site observations near the main crater suggest that the intensity of the volcanic tremor varied directly with the force of the eruption. A notable rise in the fluorine concentration of riverwater in the vicinity of the eruptive fissures occurred on the 5th day of the eruption, but it levelled off on the 6th day and then remained essentially constant. The volume and initial silica content of the lava and tephra, the explosivity and effusion rate during the earliest stage of the eruption, as well as the magnitude attained by the associated earthquakes, support earlier suggestions that these parameters are positively related to the length of the preceeding repose period. The chemical difference between the eruptive material of Hekla itself and the lavas erupted in its vicinity can be explained in terms of a density-stratified magma reservoir located at the bottom of the crust. We propose that the shape of this reservoir, its location at the west margin of a propagating rift, and its association with a crustal weakness, all contribute to the high eruption frequency of Hekla.     

Dysaerobic conditions during Heinrich events 4 and 5: Evidence from phosphorus distribution in a North Atlantic deep-sea core

Reactive phosphorus undergoes diagenetic transformation once transferred into marine sediments. The degree of regeneration and redistribution of phosphorus depends on early diagenetic and environmental conditions, which may be linked to larger scale phenomena, such as bottom water circulation, water column ventilation, and organic carbon flux. Phosphorus phases of the <50-μm-sized fraction of deep-sea sediments from core SU 90-09 (North Atlantic, 43°31′N, 30°24′W, 3375 m below sea level) have been analyzed using a sequential extraction technique (SEDEX method) to reconstruct phosphorus geochemistry during Heinrich events 4 and 5. Comparison with Holocene samples from the same site indicates that postdeposition diagenetic transformation has not affected phosphorus distribution in the deep part of the sediments. Total and reactive phosphorus average 0.40 ± 0.04 mg/g and 0.30 ± 0.05 mg/g, respectively, and are comparable to values found in analog deep-sea environments in the North Atlantic. Detrital phosphorus, the phase linked to igneous- and metamorphic-derived material, sharply increases during Heinrich events and covaries with the ice-rafted debris record, whereas authigenic and Fe-bound phosphorus phases, both influenced by redox conditions, decrease or even disappear. These findings suggest that during the deposition of Heinrich layers (HLs), environmental parameters hampered the precipitation of these phases. Large freshwater discharges in relation to iceberg surges may have provoked a temporary stratification of the water column. Accordingly, dysaerobic conditions in the sediments may have fostered the loss of dissolved phosphorus from the sediments to the water column, in a direct and rapid response to the changed conditions. Decreasing trends in organic matter elemental ratios (total organic carbon/organic phosphorus) and Rock-Eval oxygen index values, along with the presence of partly authigenic dolomite and ankerite within HLs, also support this assumption.     

Defining a Digital Earth System

In a 1998 speech before the California Science Center in Los Angeles, then US Vice‐President Al Gore called for a global undertaking to build a multi‐faceted computing system for education and research, which he termed “Digital Earth.” The vision was that of a system providing access to what is known about the planet and its inhabitants’ activities – currently and for any time in history – via responses to queries and exploratory tools. Furthermore, it would accommodate modeling extensions for predicting future conditions. Organized efforts towards realizing that vision have diminished significantly since 2001, but progress on key requisites has been made. As the 10 year anniversary of that influential speech approaches, we re‐examine it from the perspective of a systematic software design process and find the envisioned system to be in many respects inclusive of concepts of distributed geolibraries and digital atlases. A preliminary definition for a particular digital earth system as: “a comprehensive, distributed geographic information and knowledge organization system,” is offered and discussed. We suggest that resumption of earlier design and focused research efforts can and should be undertaken, and may prove a worthwhile “Grand Challenge” for the GIScience community.