Capelinhos 1957–1958, Faial, Azores: deposits formed by an emergent surtseyan eruption

The 1957–1958 eruption of Capelinhos, Faial island, Azores, involved three periods of surtseyan, hydromagmatic activity: two in 1957 and one in 1958. Deposits from this eruption are exposed both in sea cliffs cut into the flanks of the tuff cone and more distally >1 km from the vent. Five lithofacies are identified: lithofacies I is composed of even thickness beds with laterally continuous internal stratigraphy and is interpreted to have been formed by fallout. Lithofacies II consists of beds with internally discontinuous lenses, and has sand-wave structures that increase in abundance toward the outer margins of the tuff cone. This lithofacies is interpreted as having been deposited from pyroclastic surges. Lithofacies III is composed of mantle-bedded deposits with laterally discontinuous internal stratigraphy. This lithofacies is interpreted to have been formed by hybrid processes where fallout of tephra occurred simultaneously with pyroclastic surges. In the outer flanks of the tuff cone, lithofacies III grades laterally into fallout beds of lithofacies I. Lithofacies IV consists of alternating beds of coarse ash aggregates and non-aggregated fine ash, and is particularly well developed in distal regions. Some of this facies was formed by fallout. Alternating beds also occur plastered against obstacles up to 2 km from the vent, indicating an origin from wet pyroclastic surges. The orientation of plastered tephra indicates that the surges were deflected by topography as they decelerated. The distinction between surge and fallout in distal regions is uncertain because wind-drifted fallout and decelerating surge clouds can generate similar deposits. Lithofacies V consists of scoria lapilli beds interpreted to be fallout from hawaiian-style fire-fountaining in the later stages of the eruption. Juvenile pyroclasts within hydromagmatic deposits are predominantly poorly vesicular (25–60% of clasts <30% vesicles). However, on both micro- and macroscopic scales, there is a wide range in clast vesicularity (up to 70% vesicles) indicating that, although fragmentation was predominantly hydromagmatic, vesiculation and magmatic-volatile-driven fragmentation operated simultaneously.     

The properties of tuned liquid dampers using a TMD analogy

Liquid motions in shallow Tuned Liquid Dampers (TLDs) with rectangular, circular, and annular tanks, subject to harmonic base excitation, are measured experimentally. Using a Single-Degree-of-Freedom (SDOF) Tuned Mass Damper (TMD) analogy, equivalent mass, stiffness and damping of the TLD are calibrated from the experimental results. These parameters are functions of the TLD base amplitude. Some important properties of the TLD are discussed on the basis of these results.     

Amino acid geochemistry of fossil bones from the Rancho La Brea asphalt deposit,California

Low aspartic acid d:l ratios and modern collagenlike concentration values indicate that amino acids in bones from the Rancho La Brea asphalt deposit, Los Angeles, California are better preserved than amino acids in bones of equivalent age that have not been preserved in asphalt. Amino acids were recovered from 10 Rancho La Brea bone samples which range in age from less than 200 to greater than 36,000 yr. The calibrated rates of aspartic acid racemization range from 2.1 to 5.0 × 10^?6yr^?1. Although this wide range of rate constants decreases the level of confidence for age estimates, use of the larger rate constant of 5.0 × 10^?6yr^?1 provides minimum age estimates which fit the known stratigraphic and chronologic records of the Rancho La Brea deposits.     

Man,runoff and the erosion of the coastal slopes of Ashkelon,Israel

In Ashkelon two different man-environment interactions have stimulated coastal slope erosion by enhancing runoff volumes. The first type of interaction is recreation and the second is the result of Bedouin pastoral nomadism. The impact of recreation creates impervious surfaces such as walkways, parking lots, and stairways, in addition to storm sewer outlets that concentrate and enlarge runoff volumes. The impact of pastoral nomadism is limited to the crumbling of the slope surfaces by animal grazing. This creates favorable environments for rapid runoff and erosion. The results of these interactions are a coastal slope surface inundated by dense gulley networks. Large alluvial fans are also built-up at the slope base. The fans limit wave attack and re-enforce the importance of runoff as an agent of coastal slope erosion.Dr. Alan L. Marcus is Lecturer of Geomorphology     

Aluminum coordination in metaaluminous and peralkaline silicate melts

Incremental amounts of Na₂O and K₂O added to immiscible melts in the MgO-CaO-TiO₂-Al₂O₃ SiO₂ system cause a decrease in critical temperature, phase separation and change in the pattern of Al₂O₃ partitioning. Al₂O₃, which is concentrated in the low SiO₂ immiscible melts in the alkali-free system, is increasingly partitioned into the high-SiO₂ immiscible melt as the alkali/aluminium ratio is increased. However, K₂O is more effective than Na₂O in stabilizing Al₂O₂ in the SiO₂-rich melt. The coordination changes occurring in the aluminosilicate melts upon the addition of the alkali oxides are described by CaAl₂O₄+2SiOK=2KAlO₂+SiOCaOSi where K (or Na) displaces Ca as the charge-balancing cation for the networkforming AlO₄ tetrahedra. The increased stability of the AlO₄ species in the highly polymerized SiO₂-rich melt and the consequent shrinkage of the miscibility gap is ascribed to positive configurational entropy and negative enthalpy changes associated with the formation of K, Na-AlO₄ species. Element partition systematics indicate that (Na, K)AlO₂ species favor the more polymerized, CaAl₂O₄ and TiO₂ species, the less polymerized silicate structure in the melt.     

Stratigraphy of the tectonically imbricated lithological succession of the Neves Corvo mine area,Iberian Pyrite Belt,Portugal

Biostratigraphic research, based on palynomorphs and ammonoids, of the tectonically imbricated lithological succession of the Neves Corvo mine, in the Portuguese part of the Iberian Pyrite Belt, has yielded ages for all formerly recognised lithostratigraphic units. These can be assembled in three main lithological sequences: (1) detrital sandy/shale substrate (Phyllite-Quartzite Formation) of late Famennian age; (2) Volcano-Sedimentary Complex, divided into a lower and an upper suite, in which one basic, three dolerite sills and four felsic volcanic units and a mineralised package of massive sulphides are identified with ages which range from the late Famennian to the late Visean; (3) flysch succession (Mértola Formation) composed of shale and greywacke dated as late Visean to early Serpukhovian. Precise biostratigraphic dating of the sedimentrary host rocks of massive sulphide mineralisation constrains the age of the latter to the late Strunian (354.8–354.0 Ma). Three stratigraphic hiatuses, corresponding to early/middle Strunian, Tournaisian and early Visean respectively and a south-westward progressive unconformity were also recognised. Sequences 1 and 2 are related to extensional episodes while sequence 3 marks the beginning of compressive tectonic inversion which gave rise to south-westward flysch progradation in close relation to a foreland basin development. Our results lead to the reinterpretation of the tectonic structure of the Neves Corvo mine, with implications for the interpretation of the regional basin dynamics and metal exploration.Editorial handling: F. Tornos     

Calibration and validation of a model of forest disturbance in the Western Ghats,India 1920–1990

This paper introduces a new statistical method that we recommend should become standard procedure to quantify the goodness-of-fit of calibration and validation for land-use change models. We present a multiple-resolution Relative Operating Characteristic (ROC) that measures the goodness-of-fit between a reference map, which is considered reality, and a simulated map, which is a model’s output. This proposed ROC is based on: (1) multiple-resolutions, (2) soft classification, (3) sampling without replacement, and 4) explicit separation of factors of quantity versus location of land-use change. We illustrate the method with a case study in India’s Western Ghats, a biodiversity hotspot, where we have maps of cumulative forest disturbance for 1920 and 1990. We use a predictive modeling approach similar to GEOMOD in which we calibrate the model with the map of 1920, then predict the map of 1990, at which point we subject the model to validation. We show that the fit of calibration tends to be much larger than the fit of validation. Thus if a modeler assess a model by goodness-of-fit of calibration only, then the modeler will likely be over confident in the model’s predictive ability.