Lichenometric dating of debris-flow deposits in the Scottish Highlands

Debris-flow deposits, dated by lichenometry, indicate that the majority of hillslope debris flows in Scotland have occurred within the last 500 years. Progressive weathering and climatic change can be discounted as the prime cause of the increase in the incidence of debris flows. The timing of the increase suggests that it is related to landuse changes in the Scottish Highlands during the 19th and early 20th centuries. Both burning and overgrazing can be cited as potential causal factors.     

The temporal and spatial development of landslides in the axmouth-lyme regis undercliffs national nature reserve,Devon

A chronology of landsliding is presented, including suggestions as to a date for initiation. Periods of activity known from historical sources are correlated with known periods of climatic deterioration. The current morphology of the landslide slopes is closely related to the geological succession and structure. These permit the landslides and their development to be differentiated on the basis of whole slope and toe morphology, and much of the whole-slope activity can be related to conditions at the toe. Examples of geomorphological maps, slope categories maps, and cross sections are presented along with an example of the ‘evolutionary’ maps which may be derived from Ordnance Survey plans and aerial photographs. These generally indicate that weakening of materials by weathering, seepage erosion at the toe, and marine erosion result in frequent mass movement events of a low magnitude. These events ultimately influence the stability of larger slipped blocks behind, which fail less frequently. It is suggested that whole-slope failures in this region have a maximum frequency of once in 120 to 150 years, and that problems of interpretation of historical accounts may mean that it is very much less frequent than this.     

On the effect of the rigid sidewall on the dynamic stiffness of embedded circular footings

The effect of the rigid sidewall, which is usually combined with embedded footings, on the dynamic stiffness of the footings is considered. An efficient numerical technique is used to calculate the static and dynamic stiffness of circular footings embedded in a stratum. The results show that the increase in static stiffness with increasing height of the sidewall is most significant in the case of rocking. The dynamic stiffness coefficients change considerably, if the sidewall extends higher than about half the depth of embedment. The damping coefficients corresponding to vertical vibrations and rocking are likewise affected by the height of the sidewall. The damping coefficients corresponding to torsional and horizontal vibrations increase considerably with increasing height of the sidewall.     

Soil-structure interaction with Rayleigh waves

Presented is a plane-strain method for soil-structure interaction analysis consisting of the superposition of the free field motions and the interaction motions in a generalized seismic environment. The free field is modelled as a horizontally layered viscoelastic medium and the seismic environment may consist of a combination of S, P and Rayleigh waves. The soil-structure system is modelled with viscoelastic finite elements, transmitting boundaries, viscous boundaries and a three-dimensional simulation. Comparative analyses of the same structure are conducted for an input of R waves and for vertically propagating S and P waves in a rock site and sand site. In the rock site the R waves produce higher peak horizontal spectral acceleration up to 25 per cent, and a significant rocking effect at points away from the centre of gravity of the structure. However, the S and P waves show higher peak vertical spectral acceleration by up to 15 per cent at the centre of the structure. Very similar horizontal response, but higher vertical response only at the centre of the structure for S and P waves, is obtained for the sand site.     

Conduit-vent structures and related proximal deposits in the Las Cañadas caldera, Tenerife, Canary Islands

The Las Cañadas caldera wall and the outer slopes of the caldera provide three-dimensional exposures of numerous proximal-welded fallout deposits and have been mapped in detail. As a result, some parts of the Ucanca and Guajara Formations of the stratigraphy of Martí et al. (1994) have been divided into members that correspond to individual eruptions. Mapping has also revealed the occurrence of conduit-vent structures associated with proximal-welded fallout deposits. Conduit-vent structures consist of an upper flaring area and a lower narrow conduit. Conduit-vent geometry and dimensions include cylindrical plugs and eruptive fissures steeply dipping towards the caldera depression and elongated vents. The flaring area can be rather asymmetric and is usually filled by down-vent rheomorphic flow of the proximal fallout deposit. The lower conduits are filled by lava plug, agglutination of juveniles onto conduit walls and dyke intrusion with eventual dome extrusion. The eruption dynamics of welded fallout deposits and magma fragmentation within the conduit are consistent with an evolution from explosive to effusive. In this context conduit flow regimes evolve from turbulent to annular flow in which the conduit is progressively choked, and laminar flow leading to the final conduit closure.     

A preliminary investigation of strong-motion data from the French Antilles

Strong-motion networks have been operating in the Caribbean region since the 1970s, however, until the mid-1990s only a few analogue stations were operational and the quantity of data recorded was very low. Since the mid-1990s, digital accelerometric networks have been established on islands within the region. At present there are thought to be about 160 stations operating in this region with a handful on Cuba, 65 on the French Antilles (mainly Guadeloupe and Martinique), eight on Jamaica, 78 on Puerto Rico (plus others on adjacent islands) and four on Trinidad.After briefly summarising the available data from the Caribbean islands, this article is mainly concerned with analysing the data that has been recorded by the networks operating on the French Antilles in terms of their distribution with respect to magnitude, source-to-site distance, focal depth and event type; site effects at certain stations; and also with respect to their predictability by ground motion estimation equations developed using data from different regions of the world. More than 300 good quality triaxial acceleration time-histories have been recorded on Guadeloupe and Martinique at a large number of stations from earthquakes with magnitudes larger than 4.8, however, most of the records are from considerable source-to-site distances. From the data available it is found that many of the commonly-used ground motion estimation equations for shallow crustal earthquakes poorly estimate the observed ground motions on the two islands; ground motions on Guadeloupe and Martinique have smaller amplitudes and are more variable than expected. This difference could be due to regional dependence of ground motions because of, for example, differing tectonics or crustal structures or because the ground motions so far recorded are, in general, from smaller earthquakes and greater distances than the range of applicability of the investigated equations.     

Eruptive history and petrologic evolution of the Albano multiple maar (Alban Hills, Central Italy)

A comprehensive volcanological study of the Albano multiple maar (Alban Hills, Italy) using (i) ⁴⁰Ar/³⁹Ar geochronology of the most complete stratigraphic section and other proximal and distal outcrops and (ii) petrographic observations, phase analyses of major and trace elements, and Sr and O isotopic analyses of the pyroclastic deposits shows that volcanic activity at Albano was strongly discontinuous, with a first eruptive cycle at 69±1 ka producing at least two eruptions, and a second cycle with two peaks at 39±1 and 36±1 ka producing at least four eruptions. Contrary to previous studies, we did not find evidence of magmatic or hydromagmatic eruptions younger than 36±1 ka. The activity of Albano was fed by a new batch of primary magma compositionally different from that of the older activity of the Alban Hills; moreover, the REE and ⁸⁷Sr/⁸⁶Sr data indicate that the Albano magma originated from an enriched metasomatized mantle. According to the modeled liquid line of descent, this magma differentiated under the influence of magma/limestone wall rock interaction. Our detailed eruptive and petrologic reconstruction of the Albano Maar evolution substantiates the dormant state of the Alban Hills Volcanic District. Electronic Supplementary Material Supplementary material is available for this article at Editorial responsibility: J. Donnelly-Nolan An erratum to this article can be found at     

Using analytic element models to delineate drinking water source protection areas

Since 1999, Ohio EPA hydrogeologists have used two analytic element models (AEMs), the proprietary software GFLOW and U.S. EPA's WhAEM, to delineate protection areas for 535 public water systems. Both models now use the GFLOW2001 solution engine, integrate well with Geographic Information System (GIS) technology, have a user-friendly graphical interface, are capable of simulating a variety of complex hydrogeologic settings, and do not rely upon a model grid. These features simplify the modeling process and enable AEMs to bridge the gap between existing simplistic delineation methods and more complex numerical models. Ohio EPA hydrogeologists demonstrated that WhAEM2000 and GFLOW2000 were capable of producing capture zones similar to more widely accepted models by applying the AEMs to eight sites that had been previously delineated using other methods. After the Ohio EPA delineated protection areas using AEMs, more simplistic delineation methods used by other states (volumetric equation and arbitrary fixed radii) were applied to the same water systems to compare the differences between various methods. GIS software and two-tailed paired t-tests were used to quantify the differences in protection areas and analyze the data. The results of this analysis demonstrate that AEMs typically produce significantly different protection areas than the most simplistic delineation methods, in terms of total area and shape. If the volumetric equation had been used instead of AEMs, Ohio would not have protected 265 km2 of critical upgradient area and would have overprotected 269 km2 of primarily downgradient land. Since an increasing number of land-use restrictions are being tied to drinking water protection areas, this analysis has broad policy implications.