Database of giant landslides on volcanic islands—first results from the Atlantic Ocean

Giant landslides on volcanic islands represent the largest formations which can be created in a single geological moment. Such landslides are distributed across the globe and have attracted a significant amount of research interest. Yet, no coherent attempts have been made to rationalise this information into a single online resource. This report summarises information about the structure of the recently created database of giant landslides on volcanic islands and presents some observations regarding the uncertainties inherent in the inventories. The database is being prepared over a 3-year period: the first year of the project has focused on rationalising information about giant landslides around the Atlantic Ocean while the second and third years will focus on rationalising information about such landslides from the Pacific Ocean and Indian Ocean, respectively. Using this database, it should be possible to interrogate the spatial and temporal patterns of land sliding and landslide reactivation as well as to better assess the hazard and potential risks posed by giant landslides on volcanic islands. It will be particularly interesting to see if any evidence can be found for global triggers, such as eustatic or climatic changes, instead of the more commonly expounded local triggers. Ultimately, it is hoped that the database will benefit both the geoscientific community and those agencies responsible for civil defence. This work is part of the activities of the International Consortium on Landslides, namely its International Programme on Landslides (Project n. 212). The database is available from the giant landslides project webpage: https://www.irsm.cas.cz/ext/giantlandslides.     

A Computationally Efficient,Time-Dependent Model of the Solar Wind for Use as a Surrogate to Three-Dimensional Numerical Magnetohydrodynamic Simulations

Solar radiation variability spans a wide range in time, ranging from seconds to decadal and longer. The nearly 40 years of measurements of solar irradiance from space established that the total solar irradiance varies by \(\approx 0.1\%\) in phase with the Sun’s magnetic cycle. Specific intervals of the solar spectrum, e.g., ultraviolet (UV), vary by orders of magnitude more. These variations can affect the Earth’s climate in a complex non-linear way. Specifically, some of the processes of interaction between solar UV radiation and the Earth’s atmosphere involve threshold processes and do not require a detailed reconstruction of the solar spectrum. For this reason a spectral UV index based on the (FUV-MUV) color has been recently introduced. This color is calculated using SORCE SOLSTICE integrated fluxes in the FUV and MUV bands. We present in this work the reconstructions of the solar (FUV-MUV) color and Ca ii K and Mg ii indices, from 1749–2015, using a semi-empirical approach based on the reconstruction of the area coverage of different solar magnetic features, i.e., sunspot, faculae and network. We remark that our results are in noteworthy agreement with latest solar UV proxy reconstructions that exploit more sophisticated techniques requiring historical full-disk observations. This makes us confident that our technique can represent an alternative approach which can complement classical solar reconstruction efforts. Moreover, this technique, based on broad-band observations, can be utilized to estimate the activity on Sun-like stars, that cannot be resolved spatially, hosting extra-solar planetary systems.

     

On the application of the coupled finite-infinite element method to geodetic boundary-value problem

Our aim is to introduce the Coupled Finite-Infinite Element Method (CFIEM) as a new alternative approach to the Earth’s gravity field modelling. We show that if the computational domain is large enough in radial direction, one can obtain the qualitatively and quantitatively comparable solution to the solution by the Finite Element Method (FEM). We study the influence of the size of the computational domain on the final CFIEM solution as well as the successive refinement of the discretization and its convergence to the exact solution. As an input data we use the synthetic boundary conditions computed from a Synthetic Earth Gravity Model (SEGM) and we test the CFIEM solution by the data generated directly from SEGM and the solution by the FEM.     

Sedimentology and geochemistry of an exceptionally preserved last interglacial sapropel S5 in the Levantine Basin (Mediterranean Sea)

A combined study of lithological, geochemical and physical sediment properties is reported from a completely laminated S5 sapropel, recovered in three gravity cores (M40-4 SL67, M51-3 SL103, M51-3 SL104) from the Pliny Trench region of the eastern Mediterranean. The thickness of the studied sapropel S5 varies between 85 and 91 cm and tops most S5-sapropels in the Mediterranean. Based on optical features like color and thickness of laminae, the sapropels were subdivided into thirteen distinct lithostratigraphic zones. These zones, as well as the finer layering pattern within them, could be followed exactly among the three cores, indicating that the processes responsible for this variation acted at least on a regional scale. The sapropel sediment is characterized by exceptionally high porosity, which is strongly correlated with Si/Ca. This relationship implies that the sapropel is in essence an organic-matter rich diatomite and its exceptional thickness can be explained by preservation of diatoms forming a loosely packed sediment fabric. Compared to other S5 sapropels, the preservation of diatoms has apparently led to a twofold increase in the thickness of the sapropel layer. Relative abundances of 10 elements were determined at ultra-high resolution (0.2 mm) by XRF-scanner over the complete length of each sapropel including several cm of enclosing marl. An analysis of the chemical data indicates that the lowermost 13 cm of the sapropel is chemically more similar to the underlying marl and that the sediment chemistry shows different signals at different scales. The strongest pattern is the contrast between the sapropel and the surrounding marl, which is accentuated in elements indicative for redox conditions as well as terrigenous sediment input and productivity. Within the sapropel, a mm- to cm-scale layering is observed. The abundances of many elements are systematically linked to the pattern of these layers, indicating a common origin, related to productivity and/or terrigenous sediment and/or redox conditions. This pattern indicates a link to a regional climatic process, making the S5 sapropel horizon in M40-4 SL67, M51-3 SL103 and M51-3 SL104 a potential high-resolution archive of climatic variability during the last interglacial in the Mediterranean Sea and its adjacent landmasses.     

From rags to riches? Migration and intergenerational change in London's housing market, 1971–91

Summary In 1971 under half of London's young people, then living with their parents, lived in households that owned their homes, while well over half lived in rented housing. By 1991, now no longer living with their parents, less than a quarter of these young people were tenants. This paper identifies the components of that intergenerational tenure mobility, distinguishing between home ownership in more, and less, 'desirable' wards, and quantifies the role of migration in mediating the overall changes in Londoner's housing market status between 1971 and 1991. It analyses the moderating factors contributing to housing status mobility, such as labour market mobility and household type, and assesses the differential impact of these processes on men and women. ONS Longitudinal Study data for the period 1971–91 are analysed. Findings are that the aggregate changes concealed a range of housing careers. In particular, in-migrants fared less well in the London housing market than in its labour market.     

Land cover changes in small catchments in Slovakia during 1990–2006 and their effects on frequency of flood events

Statistical approach to the analysis of the relationship between the frequency of flood events and land cover (LC) changes in small catchments of Slovakia is presented in this paper. The data for identification of LC changes were taken from the 1990 and 2006 CORINE LC (CLC) data layers. They were derived by computer-aided visual interpretation of satellite images under the CLC Projects. The data about frequency of flood events in small catchments are from the period 1996–2006. Two hypotheses were formulated: (1) the greater the area of LC changes, the more frequent flood events; (2) in catchments where LC changes accelerating formation of direct runoff (e.g. urbanization, deforestation, farming) dominates, flood events are more frequent than in catchments where the prevailing LC changes (e.g. afforestation) reduce formation of direct runoff. Validity of hypotheses was tested in the framework of flood potential of catchments by two-factor ANOVA method. The obtained results indicate that (1) flood event frequency increases with the increasing total area of LC changes in a catchment. This tendency clearly manifests itself in catchments with very high flood potential. It is somewhat less distinct in catchments with moderate and high flood potentials. (2) There were no differences in flood event frequency between the group of catchments, where LC changes accelerating the formation of the direct runoff prevailed and the group of catchments where LC changes decelerating the formation of direct runoff were dominated.     

Ordovician and Cretaceous tectonothermal history of the Southern Gemericum Unit from microprobe monazite geochronology (Western Carpathians,Slovakia)

The Southern Gemericum basement in the Inner Western Carpathians experienced a polyphase regional deformation. Differences in the pre-Alpine and Alpine events have been constantly discussed. To address this, monazites from metapelites and acid metavolcanic rocks were dated using the Th–U–Pb electron microprobe method. Three monazite generations, such as Precambrian, Early Paleozoic, and Alpine, have been recognized in the greenschist facies pelites and acid metavolcanic rocks of the Southern Gemericum basement. Both inherited magmatic monazite grains in metavolcanites and rare relics of detrital monazites within the polyphase monazite grains in metapelites yielded the Precambrian age in the time span of 550–660 Ma. They prove the provenance and derivation from deeper crustal Cadomian fragments. High-Y magmatic monazites of Early Paleozoic age (444 ± 13 and 477 ± 7 Ma) have been recorded in the acid metavolcanites and their metavolcaniclastics. These ages roughly fit within the previously published magmatic zircon age determinations (at 494 ± 1.7 and 464 ± 1.7 Ma) that clearly indicate two-phase volcanic activity in the Early Paleozoic Southern Gemericum basin. The Early Paleozoic magmatic monazites were partly overprinted by the low-Y Alpine monazites (133 ± 5 and 184 ± 16 Ma) at their rims. In Al-rich metapelites, the newly formed low-Y monazites of Alpine age commonly occur, reflecting the polystage compression geodynamic evolution with three distinct peaks at 100 ± 8, 133 ± 5, and 190 ± 16 Ma, respectively. No data as the evidence of the pre-Alpine metamorphic events were observed in metapelites. Only some monazites yield the age indications for the Permian extensional thermal re-heating (260–290 Ma). The monazite age data from the Southern Gemericum basement indicate the strong overprinting due to the polyphase Alpine deformation at least in the greenschist facies conditions.     

Multi-proxy geoarchaeological study redefines understanding of the paleocoastlines and ancient harbours of Liman Tepe (Iskele, Turkey)

Determining the position of Liman Tepe's (ancient `Clazomenae') archaeological features relative to the coastline is important for understanding their intended function and reconstructing the character of Aegean maritime activities and sea-based trade. Previous attempts at reconstructing harbour locations at Liman Tepe relied on extrapolating paleoenvironments based on modern surface topography. In light of this, samples from a sediment coring survey and terrestrial and underwater archaeological excavations were analysed using multi-proxy geoarchaeological methods to determine paleoenvironmental facies. Micropaleontological (foraminifera), sedimentological (grain-size analysis) and geochemical (δ¹³C/δ¹⁸O) analyses resulted in the reconstruction of the coastal paleogeomorphology, including the presence and absence of ancient harbouring areas. Neither of the previous coastal reconstructions was supported by the new results. Instead, two separate harbouring areas were recognized, one coincident with the Early Bronze Age (4800–3900 years bp) and a second during the archaic and classical periods ( c. 2800–2400 years bp). These results emphasize the necessity for multi-proxy geoarchaeological studies when approaching coastal archaeological sites as a means to reconstruct paleocoastal geomorphology and understand ancient maritime development better .     

Analytical expressions for Fresnel volumes and interface fresnel zones of seismic body waves. Part 2: Transmitted and converted waves. Head waves

Summary Fresnel volumes and interface Fresnel zones of transmitted and head waves are studied. The relation derived for transmitted waves may also be used for converted reflected waves. Considerable attention is devoted to the penetration of Fresnel volumes across structural interfaces, particularly for head waves.     

Archaeomagnetic investigation of two mediaeval brick constructions in north Belgium and the magnetic anisotropy of bricks

Archaeomagnetic dates derived from geomagnetic field direction records in baked materials are proposed for a mediaeval brick kiln (from inclination I and declination D) and for bricks from a brick wall (from I only) in northern Belgium. They are used to verify whether a brick chronology based on the format of bricks is feasible in Flanders. The brick kiln yielded a highly reliable average magnetization direction corresponding to an archaeomagnetic date around A.D. 1650, using the British and French geomagnetic field secular variation curves as a reference, at least half a century younger than expected from historical data. The fidelity of the geomagnetic records was controlled by measuring the magnetic anisotropy of the bricks. Anisotropy of magnetic susceptibility (AMS) measurements demonstrate that the bricks have a shape related magnetic fabric, which is induced during the molding process. A test to control whether AMS can substitute for the anisotropy of thermo‐remanent magnetization (ATRM) failed because of induced changes during laboratory heating. © 2003 Wiley Periodicals, Inc.