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81.
Berit Oline Hjelstuen Atle Nygård Hans Petter Sejrup Haflidi Haflidason 《Boreas: An International Journal of Quaternary Research》2012,41(3):379-390
Throughout the last 1.1 million years repeated glaciations have modified the southern Fennoscandian landscape and the neighbouring continental shelf into their present form. The glacigenic erosion products derived from the Fennoscandian landmasses were transported to the northern North Sea and the SE Nordic Seas continental margin. The prominent sub‐marine Norwegian Channel trough, along the south coast of Norway, was the main transport route for the erosion products between 1.1 and 0.0 Ma. Most of these erosion products were deposited in the North Sea Fan, which reaches a maximum thickness of 1500 m and has nearly 40 000 km3 of sediments. About 90% of the North Sea Fan sediments have been deposited during the last 500 000 years, in a time period when fast‐moving ice streams occupied the Norwegian Channel during each glacial stage. Back‐stripping the sediment volumes in the northern North Sea and SE Nordic Seas sink areas, including the North Sea Fan, to their assumed Fennoscandian source area gives an average vertical erosion of 164 m for the 1.1–0.0 Ma time period. The average 1.1–0.0 Ma erosion rate in the Fennoscandian source area is estimated to be 0.15 mm a?1. We suggest, however, that large variations in erosion rates have existed through time and that the most intense Fennoscandian landscape denudation occurred during the time period of repeated shelf edge ice advances, namely from Marine Isotope Stage 12 (c. 0.5 Ma) onwards. 相似文献
82.
Zhang Suihan Johansson Fredrik Stille Håkan 《Geotechnical and Geological Engineering》2022,40(4):2167-2186
Geotechnical and Geological Engineering - Grout curtains are commonly constructed under dams to reduce the seepage through the rock foundation. In the design of grout curtains, empirical methods... 相似文献
83.
Vázquez Ariel Almendral Dahle Pål Abrahamsen Petter Sektnan Audun 《Computational Geosciences》2022,26(5):1223-1236
Computational Geosciences - Kriging is a standard method for conditioning surfaces to observations. Kriging works for vertical wells, but may produce surfaces that cross horizontal wells between... 相似文献
84.
Eiliv Larsen Astrid Lyså Ármann Höskuldsson Jan G. Davidsen Marie J. Nadeau Michael Power Georgios Tassis Stefan Wastegård 《第四纪科学杂志》2021,36(2):180-190
We provide the first documentation of tectonic deformation resulting from a volcanic eruption on the island of Jan Mayen. Vertical displacement of about 14 m southwest of the stratovolcano Beerenberg is associated with an eruption in ad 1732 on its southeastern flank. The age of the uplift event is bracketed by radiocarbon-dated driftwood buried by material deposited due to uplift, and by tephra from this eruption. Constraints, inferred from radiocarbon ages alone, allow for the possibility that uplift was completed prior to the ad 1732 eruption. However, the occurrence of tephra in the sediment column indicates that some displacement was ongoing during the eruption but ceased before the eruption terminated. We attribute the tectonic deformation to intrusion of shallow magma associated with the volcanic eruption. Our results complement previous studies of volcanic activity on Jan Mayan by providing precise age constraints for past volcanic activity. Also, it raises new hypotheses regarding the nature, timing and prevalence of precursor tectonic events to Jan Mayan eruptions. The uplift caused the complete isolation of a coastal lake by closing its outlet to the sea, thus landlocking the facultative migratory fish species Arctic charr (Salvelinus alpinus). 相似文献
85.
Natural Hazards - Fluvial floods can cause significant damages and are expected to increase in magnitude and frequency throughout the twenty-first century due to global warming. Alongside hazard... 相似文献
86.
Davide Lenaz Henrik Skogby Francesco Princivalle Ulf Hålenius 《Physics and Chemistry of Minerals》2006,33(7):465-474
The influence on the spinel structure of Fe3+ → Cr substitution was studied in flux-grown synthetic single crystals of the magnesiochromite–magnesioferrite (MgCr2O4–MgFe2O4) solid solution series. Samples were analysed by single-crystal X-ray diffraction, electron microprobe analyses, optical absorption and Mössbauer spectroscopy. With the exception of iron-poor samples (3–12 mol-% MgFe2O4), optical absorption and Mössbauer spectra show that iron occurs almost exclusively as trivalent Fe in the present samples. A very intense and broad absorption band at ca 7,800 cm?1 dominates the optical absorption spectra of samples with higher Fe-contents. The appearance of this band is related to a distinct structural disorder of Fe3+ and a development of magnetic ordering as demonstrated by Mössbauer spectra. Profound composition-related changes are observed in the Mössbauer spectra, which are magnetically unsplit in the range 2–41 mol-% magnesioferrite, but become magnetically split in the range 59–100 mol-% magnesioferrite. Structural parameters a 0 and M–O increase with magnesioferrite content and inversion degree, while u and T–O decrease. Our study confirms the previously reported (Lavina et al. 2002) influence of Fe3+ at the M site on T–O bond lengths in the spinel structure. 相似文献
87.
Long-term summer temperature variations in the Pyrenees 总被引:4,自引:0,他引:4
Two hundred and sixty one newly measured tree-ring width and density series from living and dry-dead conifers from two timberline
sites in the Spanish Pyrenees were compiled. Application of the regional curve standardization method for tree-ring detrending
allowed the preservation of inter-annual to multi-centennial scale variability. The new density record correlates at 0.53
(0.68 in the higher frequency domain) with May–September maximum temperatures over the 1944–2005 period. Reconstructed warmth
in the fourteenth to fifteenth and twentieth century is separated by a prolonged cooling from ∼1450 to 1850. Six of the ten
warmest decades fall into the twentieth century, whereas the remaining four are reconstructed for the 1360–1440 interval.
Comparison with novel density-based summer temperature reconstructions from the Swiss Alps and northern Sweden indicates decadal
to longer-term similarity between the Pyrenees and Alps, but disagreement with northern Sweden. Spatial field correlations
with instrumental data support the regional differentiation of the proxy records. While twentieth century warmth is evident
in the Alps and Pyrenees, recent temperatures in Scandinavia are relatively cold in comparison to earlier warmth centered
around medieval times, ∼1450, and the late eighteenth century. While coldest summers in the Alps and Pyrenees were in-phase
with the Maunder and Dalton solar minima, lowest temperatures in Scandinavia occurred later at the onset of the twentieth
century. However, fairly cold summers at the end of the fifteenth century, between ∼1600–1700, and ∼1820 were synchronized
over Europe, and larger areas of the Northern Hemisphere. 相似文献
88.
The inflow of Atlantic Water to the Nordic seas from mid–late Younger Dryas to earliest Holocene (12 450–10 000 a BP) is reconstructed on the basis of a high‐resolution core (LINK14) from 346 m water depth on the east Faroe shelf. We have analysed the distribution of planktic and benthic foraminifera, stable isotopes and ice‐rafted debris (IRD), and calculated absolute temperatures and salinities by transfer functions. During the investigated time period there was almost continuous inflow of Atlantic Water to the Nordic seas. Deposition of IRD during the mid–late Younger Dryas and Pre‐Boreal coolings indicates the presence of melting icebergs and that summer sea surface temperatures were low. The east–west temperature gradient across the Faroe–Shetland Channel was much steeper than today. The cold conditions around the Faroe Islands are attributed to stronger East Greenland and East Icelandic currents than at present. The near‐continuous inflow of Atlantic Water is consistent with published evidence suggesting that deep convection took place in the Nordic seas, although the convection sites probably had shifted to a more easterly position than at present. Around the time of deposition of the Saksunarvatn Tephra c. 10 350 a BP, sea surface temperatures increased to the present level. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
89.
Ohne Zusammenfassung
English Summary: Lake trout and its prey fauna in Swiss mountain lakes)
Die Nahrungsfauna wurde vonGrim⇘s, Nahrungs?kologie und Wachstum der Fische vonNilsson bearbeitet. 相似文献
90.
ABSTRACTHydrogeological hazards are increasingly causing damage worldwide due to climatic and socio-economic changes. Building resilient communities is crucial to reduce potential losses. To this end, one of the first steps is to understand how people perceive potential threats around them. This study aims at exploring how risk awareness of, and preparedness to, face hydrological hazards changes over time. A cohort study was carried out in two villages in the northeastern Italian Alps, Romagnano and Vermiglio, affected by debris flows in 2000 and 2002. Surveys were conducted in 2005 and 2018, and the results compared. The survey data show that both awareness and preparedness decreased over time. We attribute this change to the fact that no event had occurred in a long time and to a lack of proper risk communication strategies. The outcomes of this study contribute to socio-hydrological modelling by providing empirical data on human behaviour dynamics. 相似文献