Seismic activity related to the 2000 eruption of the Hekla volcano, Iceland     

Heidi Soosalu  Páll Einarsson  Bergþóra S. Þorbjarnardóttir 《Bulletin of Volcanology》2005,68(1):21-36

The 2000 Hekla eruption took place from February 26 to March 8. Its seismic expressions were a swarm of numerous small earthquakes related to its onset, and low-frequency volcanic tremor that continued throughout the eruption. A swarm of small earthquakes was observed some 80 min before the onset of the eruption, and the size of the events increased with time. Low-frequency volcanic tremor, with a characteristic frequency band of 0.5–1.5 Hz and dominant spectral peak(s) at 0.7–0.9 Hz, became visible at 18:19 GMT on February 26, marking the onset of the eruption. The tremor amplitude rose quickly and was very high in the beginning of the eruption. However, it soon began to decrease after about an hour. In general, the seismic activity related to the 2000 Hekla eruption was very similar to what was observed in the previous eruption in 1991. Based on knowledge gained from seismicity and strain observations from 1991, this was the first time that a Hekla eruption was predicted.Editorial responsibility: J Stix  相似文献   

Crustal structure in Alaska     

Eduard Berg   《Tectonophysics》1973,20(1-4):165-182

Knowledge of the crustal structure is still fragmentary, despite the stimulus to geophysical work provided by the earthquake of March 28, 1964 (GMT), the underground nuclear explosion LONGSHOT, and the June 1967 series of earthquakes in the Fairbanks area. The most reliable information about struc ture has come from a combination of seismic explosion-refraction profiles, gravity surveys, and magnetic surveys. This report is a summary of recent investigations, but the results are not adequate to permit unambiguous generalizations about crustal structure.  相似文献   

Nomogram for the construction of flow nets near singular boundary points     

A.Vanden Berg 《Journal of Hydrology》1972

Mathematical models of groundwater flow usually lack precision near singular points along an irregular boundary. Near such points the influence of the configuration of the flow net in the interior of the region becomes negligible and the flow net is almost entirely determined by the shape of the boundary. Complex variable theory provides a convenient means for the construction of flow nets in areas between two intersecting straight line boundaries which may be either streamlines or potential lines. A nomogram has been constructed for rapid determination of values of the flow potential at a sufficient number of points in a wedge of any angle to construct a reasonably accurate flow net with relative ease.  相似文献   

Das Geschwindigkeitsprofil in Flüssen     

Prof. Dr. Hellmut Berg 《Pure and Applied Geophysics》1956,34(1):260-267

Zusammenfassung Aus Geschwindigkeitsmessungen im Rhein werden mittlere vertikale logarithmische Geschwindigkeitsprofile für verschiedene Oberflächengeschwindigkeiten hergeleitet und daraus Werte für den Rauhigkeitsparameter und die Schubspannungsgeschwindigkeit bestimmt. Danach kann die Strömung im Rhein als turbulente Strömung über einer rauhen Unterlage angesehen werden. Die Abweichungen einzelner Me\reihen von der mittleren Geschwindigkeitsverteilung in der Vertikalen werden diskutiert.

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Summary Average logarithmic profiles of velocity as a function of the velocity on the surface of the Rhine are deduced and also values of the roughness length and the friction velocity («Schubspannungsgeschwindigkeit»). From that the flow of the Rhine can be considered as a turbulent flow over a rough ground. The differences between the different sets of measurements and the average profile of velocity are discussed.

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Résumé Des profils logarithmiques verticaux de la vitesse sont déduits en fonction de la vitesse superficielle du Rhin. En outre des valeurs sont données pour le paramètre de grossièreté et pour la vitesse de friction («Schubspannungsgeschwindigkeit»). A cause de ces dates le courant du Rhin peut Être interprété comme un courant se déroulant sur une couche bosselée. Les variations des séries diverses de mesures (comparées au profil moyen) sont discutées.

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Vortrag gehalten am 7. April 1956 auf der 4. Allgem. Versammlung derSocietà Italiana di Geofisica e Meteorologia (Genova: 5.–7. April 1956).  相似文献   

Analysis of Ultimate Fossil Fuel Reserves and Associated CO2 Emissions in IPCC Scenarios     

Peter Berg  Anthony Boland 《Natural Resources Research》2014,23(1):141-158

The Intergovernmental Panel on Climate Change (IPCC) commissioned a special report on emissions scenarios in 2000 so as to forecast global carbon dioxide (CO₂) emissions for a variety of assumptions. These scenarios have been subjected to a multitude of criticisms, alleging overoptimistic predictions for fossil fuel production rates. Intrigued by this controversy, this paper employs the Hubbert linearization technique to solve for ultimately recoverable resources (URR) of fossil fuels for six significant IPCC scenarios. The predictions are substantially higher than geological URR estimates found in recent literature, ranging from 19 to over 200% higher for oil, 16 to over 500% for coal, and 171 to over 500% for natural gas, depending on the scenario. Subsequently, the atmospheric CO₂ concentrations resulting from full consumption of URR related to IPCC data, as well as literature-based URR, are determined with a simple model. The former concentrations range from 640 to over 1,300 ppm. In comparison, the peak-based URR in the literature yield 463–577 ppm. All of these figures are higher than the 450 ppm ‘threshold’ which some see as critical. Therefore, despite peaking fossil fuels, concern over climate change is still warranted. At the same time, the fossil fuel production inputs to the IPCC’s CO₂ emissions models appear predominantly overoptimistic, which calls into question the accuracy of the climate change assessment outputs. Moving forward, the IPCC is encouraged to re-assess its fossil fuel forecasts, incorporating more reasonable scenarios for peak production of fossil fuels.  相似文献   

El Niño-Southern Oscillation impacts on winter winds over Southern California     

Neil Berg  Alex Hall  Scott B. Capps  Mimi Hughes 《Climate Dynamics》2013,40(1-2):109-121

Changes in wintertime 10 m winds due to the El Niño-Southern Oscillation are examined using a 6 km resolution climate simulation of Southern California covering the period from 1959 through 2001. Wind speed statistics based on regional averages reveal a general signal of increased mean wind speeds and wind speed variability during El Niño across the region. An opposite and nearly as strong signal of decreased wind speed variability during La Niña is also found. These signals are generally more significant than the better-known signals in precipitation. In spite of these regional-scale generalizations, there are significant sub-regional mesoscale structures in the wind speed impacts. In some cases, impacts on mean winds and wind variability at the sub-regional scale are opposite to those of the region as a whole. All of these signals can be interpreted in terms of shifts in occurrences of the region’s main wind regimes due to the El Niño phenomenon. The results of this study can be used to understand how interannual wind speed variations in regions of Southern California are influenced by the El Niño phenomenon.  相似文献   

The role of negative CO2 emissions for reaching 2 °C—insights from integrated assessment modelling     

Detlef P. van Vuuren  Sebastiaan Deetman  Jasper van Vliet  Maarten van den Berg  Bas J. van Ruijven  Barbara Koelbl 《Climatic change》2013,118(1):15-27

Limiting climate change to 2 °C with a high probability requires reducing cumulative emissions to about 1600 GtCO₂ over the 2000–2100 period. This requires unprecedented rates of decarbonization even in the short-run. The availability of the option of net negative emissions, such as bio-energy with carbon capture and storage (BECCS) or reforestation/afforestation, allows to delay some of these emission reductions. In the paper, we assess the demand and potential for negative emissions in particular from BECCS. Both stylized calculations and model runs show that without the possibility of negative emissions, pathways meeting the 2 °C target with high probability need almost immediate emission reductions or simply become infeasible. The potential for negative emissions is uncertain. We show that negative emissions from BECCS are probably limited to around 0 to 10 GtCO₂/year in 2050 and 0 to 20 GtCO₂/year in 2100. Estimates on the potential of afforestation options are in the order of 0–4 GtCO₂/year. Given the importance and the uncertainty concerning BECCS, we stress the importance of near-term assessments of its availability as today’s decisions has important consequences for climate change mitigation in the long run.  相似文献   

Exchange of Nitrogen and Phosphorus Between a Shallow Lagoon and Coastal Waters     

Melanie Hayn  Robert Howarth  Roxanne Marino  Neil Ganju  Peter Berg  Kenneth H. Foreman  Anne E. Giblin  Karen McGlathery 《Estuaries and Coasts》2014,37(1):63-73

West Falmouth Harbor, a shallow lagoon on Cape Cod, has experienced a threefold increase in nitrogen load since the mid- to late 1990s due to input from a groundwater plume contaminated by a municipal wastewater treatment plant. We measured the exchange of nitrogen and phosphorus between the harbor and the coastal waters of Buzzards Bay over several years when the harbor was experiencing this elevated nitrogen load. During summer months, the harbor not only retained the entire watershed nitrogen load but also had a net import of nitrogen from Buzzards Bay. During the spring and fall, the harbor had a net export of nitrogen to Buzzards Bay. We did not measure the export in winter, but assuming the winter net export was less than 112 % of the load, the harbor exported less than half of the watershed nitrogen load on an annual basis. For phosphorus, the harbor had a net import from coastal waters in the spring and summer months and a net export in the fall. Despite the large increase in nitrogen load to the harbor, the summertime import of phosphorus from Buzzards Bay was sufficient to maintain nitrogen limitation of primary productivity during the summer. Our findings illustrate that shallow systems dominated by benthic producers have the potential to retain large terrestrial nitrogen loads when there is sufficient supply of phosphorus from exchange with coastal waters.  相似文献