Thin Ash Layers Research Articles

Volcanic Ash Resuspension in Patagonia: Numerical Simulations and Observations

Resuspension of pyroclastic deposits occurs under specific atmospheric and environmental conditions and typically prolongs and exacerbates the impact associated with the primary emplacement of tephra fallout and pyroclastic density current deposits. An accurate forecasting of the phenomenon, to support Volcanic Ash Advisory Centers (VAACs) and civil aviation management, depends on adapting volcanic ash transport and dispersion models to include specific ash emission schemes. Few studies have attempted to model the mechanisms of emission and transport of windblown volcanic ash, and a systematic study of observed cases has not been carried out yet. This manuscript combines numerical simulations along with a variety of observational data to examine the general features of ash resuspension events in northern Patagonia following the 2011 Cordón Caulle eruption (Chile). The associated outcomes provide new insights into the spatial distribution of sources, frequency of events, transport patterns, seasonal and diurnal variability, and spatio-temporal distribution of airborne ash. A novel modelling approach based on the coupling between Advanced Research core of the Weather Research and Forecasting (WRF-ARW) and FALL3D models is presented, with various model improvements that allow overcoming some limitations in previous ash resuspension studies. Outcomes show the importance of integrating source information based on field measurements (e.g., deposit grain size distribution and particle density). We provide evidence of a strong diurnal and seasonal variability associated with the ash resuspension activity in Patagonia. According to the modelled emission fluxes, ash resuspension activity was found to be significantly more intense during daytime hours. Satellite observations and numerical simulations strongly suggest that major emission sources of resuspended ash were distributed across distal areas (>100 km from the vent) of the Patagonian steppe, covered by a thin layer of fine ash. The importance of realistic soil moisture data to properly model the spatial distribution of emission sources is also highlighted.

Patterns of Fine Ash Dispersal Related to Volcanic Activity at West Mata Volcano, NE Lau Basin

Extensive deep (>1500 m) non-hydrothermal ash-rich plumes were present in the water column surrounding West Mata submarine volcano (NE Lau basin) during eruptive phases, but were absent when West Mata was quiescent. Deep ash plumes were chemically distinct from hydrothermal plumes originating at West Mata and other hydrothermal sources in the region, and were dominated by very fine shards compositionally similar to the lava erupting at the ~1200 m summit with morphologies indicative of magma degassing and shattering. Deep ash plume layers occurred at variable water depths (and distances above the seafloor) and were transported by local currents to 10’s of km from West Mata. We interpret these deep ash plumes to be syn-eruptively generated ash transported downslope via sediment gravity flows of varying magnitudes, runout distances, and liftoff densities. Final deposition of individual particles will be by settling from suspension (i.e., fallout deposits). The mechanism for initiating gravity flows is uncertain, but their spatial and temporal distribution suggests that eruption column collapse and/or mobilization of unstable volcaniclasts accumulating on steep slopes during the eruption are likely sources. Turbidity within the deep ash plumes decreased by 80% over a 3 week period in 2017, suggesting the eruption that created a new deposit, constrained between March 2016 and November 2017, was likely active as recently as a few weeks to months prior to the FK171110 expedition. Similar deep ash plumes have been observed surrounding other erupting submarine volcanoes. This pattern of syn-eruptive dispersal suggests that fine ash does not have to be lofted high into the water column in event plumes, or enter the ocean from subaerial sources, to be dispersed by local currents and contribute to fallout deposits in regional and distal sediments, which may appear as cryptotephra or thin ash layers if the ash supply exceeds pelagic sedimentation rates; deposits that are often attributed to subaerial eruptions alone. These results also suggest that the presence of deep ash plumes surrounding a submarine volcanic edifice, along with a magmatic-hydrothermal plume above the summit, may be a valuable diagnostic exploration tool for identifying active, or very recently active, submarine eruptions.

Grand Sarcoui volcano (Chaîne des Puys, Massif Central, France), a case study for monogenetic trachytic lava domes

The Grand Sarcoui is a prominent trachytic volcano of the intraplate Quaternary volcanic field of Chaîne des Puys (Massif Central, France), which fulfills basic requirements for being qualified as monogenetic. Grand Sarcoui looks like a simple axisymmetric lava dome, but close observation reveals a complex and dissymmetric structure and composition. The construction of the dome, about 12.5ka ago, combined both endogenous and exogenous growth which resulted in variable modes of emplacement and textures of the lava. One of its most interesting features is a large (~0.29 106m2) fan of deposits bearing hummocks and secondary hydro-eruption craters. Cross sections of these deposits demonstrate that they originated from a sector collapse accompanied by a blast-like event. The dome is covered by a thin layer of lapilli and ash, attributed to a delayed summit eruption which occurred about 10.6ka ago, surprisingly late after its construction. So, this volcano has, at a reduced scale, features that are more usually observed in large composite volcanoes. However, some of these features differ slightly from those that have been documented to date, and they remain partly unexplained. This shows that monogenetic, well preserved, trachytic lava domes, are uncommon and poorly known, unlike rhyolitic, andesitic and dacitic domes.

Ash aggregation during the 11 February 2010 partial dome collapse of the Soufrière Hills Volcano, Montserrat

On 11 February 2010, Soufrière Hills Volcano, Montserrat, underwent a partial dome collapse (~50×106m3) and a short-lived Vulcanian explosion towards the end. Three main pyroclastic units were identified N and NE of the volcano: dome-collapse pyroclastic density current (PDC) deposits, fountain-collapse PDC deposits formed by the Vulcanian explosion, and tephra-fallout deposits associated with elutriation from the dome-collapse and fountain-collapse PDCs (i.e. co-PDC fallout deposit). The fallout associated with the Vulcanian explosion was mostly dispersed E and SE by high altitude winds. All units N and NE of the volcano contain variable amounts and types of particle aggregates, although the co-PDC fallout deposit is associated with the largest abundance (i.e. up to 24wt%). The size of aggregates found in the co-PDC fallout deposit increases with distance from the volcano and proximity to the sea, reaching a maximum diameter of 12mm about 500m from the coast. The internal grain size of all aggregates have nearly identical distributions (with Mdϕ≈4–5), with particles in the size categories >3ϕ (i.e. <250μm) being distributed in similar proportions within the aggregates but in different proportions within distinct internal layers. In fact, most aggregates are characterized by a coarse grained central core occupying the main part of the aggregate, coated by a thin layer of finer ash (single-layer aggregates), while others have one or two additional layers accreted over the core (multiple-layer aggregates). Calculated aggregate porosity and settling velocity vary between 0.3 and 0.5 and 11–21ms−1, respectively. The aggregate size shows a clear correlation with both the core size and the size of the largest particles found in the core. The large abundance of aggregates in the co-PDC fallout deposits suggests that the buoyant plumes elutriated above PDCs represent an optimal environment for the formation (particle collision) and development (aggregate layering) of particle aggregates. However, specific conditions are required, including i) a large availability of water (in this case provided by the steam plumes associated with the entrance of PDCs into the ocean), ii) presence of plume regions with different grain-size features (i.e. both median size and sorting) that allows for the development of multiple layers, iii) strong turbulence that permits both particle collision and the transition of the aggregates through different plume regions, iv) presence of hot regions (e.g. PDCs) that promote aggregate preservation (in this case also facilitated by the presence of sea salt).

Immobile and mobile elements during the transition of volcanic ash to bentonite – An example from the early Palaeozoic sedimentary section of the Baltic Basin

In order to check the immobility and mobility of elements during conversion of acidic volcanic glass to bentonites in normal marine environments, we studied the composition of three altered volcanic ash layers from the Palaeozoic of the Baltoscandian Region, correlated through different facies. Regular changes in element concentrations in accordance with loss and gain of material during the transformation of volcanic ash indicate that Al, Nb, Ti, Zr, Sn, Pt, Ta, Hf and Th were generally immobile and can be used for the interpretation of source magma and correlation of ash layers. Cd behaves similarly with immobile elements and this can be explained with preservation only of the immobile portion of Cd that is fixed in phenocrysts. In bentonites in shales during the formation of kaolinite, the data indicate small-scale mobility of Al and Cd. In lime muds where K-feldspar forms from volcanic ash, Ta, Hf and Th reveal some small scale mobility. These slightly mobile elements must be used with caution for interpretation of thin ash layers with thicknesses of <1cm. Sc, V, Ga, Y and Rare Earth Elements widely used for the interpretation of bentonites have noticeable mobility and can thus be used only semi-quantitatively or qualitatively in the bulk bentonite.

Volcanic ash in bare ice south of Sør Rondane Mountains, Antarctica: geochemistry, rock magnetism and nondestructive magnetic detection with SQUID gradiometer

Nondestructive magnetic detection of tephra layers in ice cores will be an important method to identify and correlate stratigraphic horizons of ice bearing volcanic ash particles. Volcanic ash particles were extracted from tephra-bearing ice samples collected from Nansen Ice Field south of the Sor Rondane Mountains, Antarctica. Particles are fresh glassy volcanic ash with diameters of ~50 μm, and chemical composition of the matrix glass belongs to a low-K basaltic andesite group, ranging from SiO2 60–62 wt% and K2O 0.40–0.50 wt%. Considering the grain size of ash particles and chemical composition of volcanic glass, the ash in tephra-bearing ice samples might be originated from the South Sandwich Islands located 2800 km northwest of the sampling sites. Correlations on major element concentrations with tephra layers associated with South Sandwich Islands in EPICA-Dome C, Vostok, and Dome Fuji ice cores show high similarity. Rock magnetic experiments show that the magnetic mineral is pseudo-single-domain titanomagnetite with ulvospinel content of 0.2–0.35 mixed with single-domain to superparamagnetic (titano)magnetite. Small blocks of the tephra-bering ice were measured with a SQUID gradiometer at 1-mm intervals with a spatial resolution of ~3 mm. With DC magnetic field of 25 mT, magnetic signal could be enhanced and detected for all the samples including the one with invisible amount of tephra particles. In order to simulate a thin ash layer in ice core, volcanic ash particles extracted from the tephra-bearing ice were used to fabricate a thin ash layer, which were subsequently magnetized, measured with the gradiometer. The noise level for Z axis gradiometer was about 0.6 pT. Detection limit for a half-cylinder with 29 mm radius and a thickness of 1 mm uniformly magnetized in X axis direction is ~9 × 10−5 A/m, which could be improved down to ~2 × 10−6 A/m by reducing the sensor-to-sample distance to 0.5 mm.

Insulation effects of Icelandic dust and volcanic ash on snow and ice

In the Arctic region, Iceland is an important source of dust due to ash production from volcanic eruptions. In addition, dust is resuspended from the surface into the atmosphere as several dust storms occur each year. During volcanic eruptions and dust storms, material is deposited on the glaciers where it influences their energy balance. The effects of deposited volcanic ash on ice and snow melt were examined using laboratory and outdoor experiments. These experiments were made during the snow melt period using two different ash grain sizes (1 ϕ and 3.5 ϕ) from the Eyjafjallajokull 2010 eruption, collected on the glacier. Different amounts of ash were deposited on snow or ice, after which the snow properties and melt were measured. The results show that a thin ash layer increases the snow and ice melt but an ash layer exceeding a certain critical thickness caused insulation. Ash with 1 ϕ in grain size insulated the ice below at a thickness of 9–15 mm. For the 3.5 ϕ grain size, the insulation thickness is 13 mm. The maximum melt occurred at a thickness of 1 mm for the 1 ϕ and only 1–2 mm for 3.5 ϕ ash. A map of dust concentrations on Vatnajokull that represents the dust deposition during the summer of 2013 is presented with concentrations ranging from 0.2 up to 16.6 g m−2.

Paleosols beneath a lava flow in the southern basin of Mexico: The effect of heat on the paleopedological record

Volcanic activity affects past and present landscapes. Here we present a case study related to the heat impact of the Xitle lava flow on the former soil cover. The eruption occurred 1670yearsB.P., in south Mexico City. The evaluated properties include those related to the “soil memory”, used as tools of paleoenvironmental interpretation in volcanic paleosols: macro and micromorphology, color, grain size distribution, magnetic susceptibility, and carbon and nitrogen contents. Changes of these properties by the heat influence are relevant for an adequate paleoenvironmental reconstruction. Two sites and three soil profiles are selected to show soil modifications by the volcanic activity. The two sites represent the following: 1) slightly transformed paleosol buried by the lava flow, but separated from it by a 10cm thick volcanic ash layer (site Cuicuilco-ENAH); 2) moderately and strongly transformed paleosols (two profiles inside the Copilco archeological zone). One of the Copilco profiles represents a buried paleosol with a very thin (3cm) ash layer on top, at the contact with the lava; the second profile is the most affected by the lava flow, as it is directly beneath the lava. All studied paleosols are sandy, have a low amount of organic matter, narrow C/N ratios, and very high values of magnetic susceptibility. The strongest modifications are observed in the upper horizons, which are in contact with the lava. However, the presence of the ash layer minimizes the heat effect. Despite the observed modifications, it is possible to establish three cycles of soil formation in the paleolandscape. The first, and the oldest, related to the development of a Luvisol type soil, indicates a longer time of landscape stability. During the second cycle a pedosediment with a high concentration of artifacts was formed. The last and the youngest cycle includes the Ab and the AEb horizons (present only in Copilco). They form by an Andosol type pedogenesis, which reflects a shorter time of soil development. The presence of the AEb horizon is interpreted as the result of the degradation of the Ab horizon, either due to the heat effect of the lava, or to cultivation and irrigation practiced by the pre-Hispanic communities.

Time-lagged ensemble simulations of the dispersion of the Eyjafjallajökull plume over Europe with COSMO-ART

Abstract. An extended version of the German operational weather forecast model was used to simulate the ash dispersion during the eruption of the Eyjafjallajökull. As an operational forecast was launched every 6 hours, a time-lagged ensemble was obtained. Sensitivity runs show the ability of the model to simulate thin ash layers when an increased vertical resolution is used. Calibration of the model results with measured data allows for a quantitative forecast of the ash concentration. After this calibration an independent comparison of the simulated number concentration of 3 μm particles and observations at Hohenpeißenberg gives a correlation coefficient of 0.79. However, this agreement could only be reached after additional modifications of the emissions. Based on the time lagged ensemble the conditional probability of violation of a certain threshold is calculated. Improving the ensemble technique used in our study such probabilities could become valuable information for the forecasters advising the organizations responsible for the closing of the airspace.

Brave, and Mudlarking, Dead Horse Beach

Brave, and Mudlarking, Dead Horse Beach January Gill O’Neil (bio) Brave A thin layer of ash, fine debris, probably bone coated the windshield as we passed exit after exit for the Garden State Parkway. We took detours and back roads while police blocked every onramp. Blue lights pulsing. Officers in yellow hazard vests stood next to their squad cars as we drove past midnight: my soon-to-be husband, mother-in-law, brother-in-law, and me in a 1992 Grand Marquis on our way to Virginia. On the radio, nothing but news and static. All of us silent, sleepy, edgy, uncertain, both absent and present on an empty highway driving past New York City. I would never tell my daughter that some nights I lie awake listening for the raccoon I know is in the attic [End Page 132] but pretend isn’t there. The scratching, the heavy scampering— she hears it, too. If he were here, daddy would check things out. If he were here, mommy would not feel lonely. We pretend to be brave, bang on the walls, play loud music to scare it away, pray it does not have cubs. Marriages fail. There is no one else to go up there and get the little fucker. On our day in court my lawyer was late, so the judge moved our case to the afternoon docket. We sat for hours you on the left side, me on the right listening to failure after failure, the quick dissolve of marriages into oblivion. I remember thinking Hallmark doesn’t make a card for this: the moment when the judge calls your name and uses words such as irreconcilable, broken, and final [End Page 133] and a swell, no a surge of tears breaks as the judge uncouples us. You cried, too. Neither of us looked at the other or spoke. When I turned around You were gone. You had left the building. Before we arrived at the hotel we took engagement photos in our wrinkled clothes. And before that we watched the sun rise as we crossed the Chesapeake Bay Bridge Tunnel. And before that we listened to Howard Stern around 5 a.m. broadcast live, trying to find the right words. Any words. And before that you took the wheel from your brother so he could get some sleep. And before that, silence. And before that you held my hand as we rode in the back seat. And before that we were not allowed on the Garden State Parkway. [End Page 134] And before that we stopped for gas, sandwiches, checked the check engine light somewhere in Connecticut. And before that there was a toll on the Tobin Bridge. And before that I was on the phone with the maid of honor who would ride the bus from Texas to Virginia to arrive by Saturday. I thought she was crazy. And before that I was on the phone with my father who said, be careful and I love you. And before that no flights were allowed out of Logan Airport or anywhere. And before that I said yes. And before that you said yes. And before that I asked, Should we go through with the wedding? I would never tell my daughter male raccoons have no part in raising their young. [End Page 135] Mudlarking, Dead Horse Beach They’re buried just past Winter Islandwhere the two-lane road windsaround the boardwalk at Salem Willows.Dead Horse Beach, where the cold-bloodedflanks and loins of work horseswere discarded far from Salem Proper.Here, the earth has taken them backand given us silt. Why have I come hereat low tide, mudlarkingfor bits of bottle and bone?Even the renegade skyhas turned its back on everycumulonimbus to be here.It is the day before Mother’s Day,the kids with him for the weekend.A breeze blows the new leavesof the willow trees sideways,their low-hanging branches lift and fallagainst the wind, and on a hill just abovea family reunion, the backs of brightly coloredlawn chairs face me, I hear the occasional laugh,smell the...

CARIBIC aircraft measurements of Eyjafjallajökull volcanic clouds in April/May 2010

Abstract. The Civil Aircraft for the Regular Investigation of the Atmosphere Based on an Instrument Container (CARIBIC) project investigates physical and chemical processes in the Earth's atmosphere using a Lufthansa Airbus long-distance passenger aircraft. After the beginning of the explosive eruption of the Eyjafjallajökull volcano on Iceland on 14 April 2010, the first CARIBIC volcano-specific measurement flight was carried out over the Baltic Sea and Southern Sweden on 20 April. Two more flights followed: one over Ireland and the Irish Sea on 16 May and the other over the Norwegian Sea on 19 May 2010. During these three special mission flights the CARIBIC container proved its merits as a comprehensive flying laboratory. The elemental composition of particles collected over the Baltic Sea during the first flight (20 April) indicated the presence of volcanic ash. Over Northern Ireland and the Irish Sea (16 May), the DOAS system detected SO2 and BrO co-located with volcanic ash particles that increased the aerosol optical depth. Over the Norwegian Sea (19 May), the optical particle counter detected a strong increase of particles larger than 400 nm diameter in a region where ash clouds were predicted by aerosol dispersion models. Aerosol particle samples collected over the Irish Sea and the Norwegian Sea showed large relative enhancements of the elements silicon, iron, titanium and calcium. Non-methane hydrocarbon concentrations in whole air samples collected on 16 and 19 May 2010 showed a pattern of removal of several hydrocarbons that is typical for chlorine chemistry in the volcanic clouds. Comparisons of measured ash concentrations and simulations with the FLEXPART dispersion model demonstrate the difficulty of detailed volcanic ash dispersion modelling due to the large variability of the volcanic cloud sources, extent and patchiness as well as the thin ash layers formed in the volcanic clouds.

Determining the contribution of volcanic ash and boundary layer aerosol in backscatter lidar returns: A three-component atmosphere approach

[1] A solution of the lidar equation is discussed, that permits combining backscatter and depolarization measurements to quantitatively distinguish two different aerosol types with different depolarization properties. The method has been successfully applied to simultaneous observations of volcanic ash and boundary layer aerosol obtained in Exeter, United Kingdom, on 16 and 18 April 2010, permitting the contribution of the two aerosols to be quantified separately. First a subset of the atmospheric profiles is used where the two aerosol types belong to clearly distinguished layers, for the purpose of characterizing the ash in terms of lidar ratio and depolarization. These quantities are then used in a three-component atmosphere solution scheme of the lidar equation applied to the full data set, in order to compute the optical properties of both aerosol types separately. On 16 April a thin ash layer, 100–400 m deep, is observed (average and maximum estimated ash optical depth: 0.11 and 0.2); it descends from ∼2800 to ∼1400 m altitude over a 6-hour period. On 18 April a double ash layer, ∼400 m deep, is observed just above the morning boundary layer (average and maximum estimated ash optical depth: 0.19 and 0.27). In the afternoon the ash is entrained into the boundary layer, and the latter reaches a depth of ∼1800 m (average and maximum estimated ash optical depth: 0.1 and 0.15). An additional ash layer, with a very small optical depth, was observed on 18 April at an altitude of 3500–4000 m. By converting the lidar optical measurements using estimates of volcanic ash specific extinction, derived from other works, the observations seem to suggest approximate peak ash concentrations of ∼1500 and ∼1000 μg/m3, respectively, on the two observations dates.

Effect of isopropanol rinse on adhesion of plasma-treated carbon-fiber reinforced epoxy composites

In this article, we present a comparative assessment of adhesion in plasma-treated carbon fiber reinforced epoxy specimens subject to a post plasma isopropanol rinse. We find that plasma-treated and rinsed samples have better average adhesion than otherwise comparable unrinsed samples and attribute this finding to removal of a thin layer of ash from the plasma-treated surface. Using SEM, XPS, SIMS, and FTIR as diagnostic techniques, we are able to monitor the effects of the rinse on surface chemical functionalization.

Response of Early Eocene deep-water benthic foraminifera to volcanic ash falls in the Polish Outer Carpathians: Palaeocological implications

Lower Eocene sediments of the Subsilesian Unit of the Polish Carpathians contain bentonite layers that were deposited in a deep-water basinal environment. Foraminiferal assemblages occurring within the bentonites and in the surrounding shales show important differences in taxonomical composition, the proportions of ecological groups, and test composition. Foraminiferal assemblages collected from bentonites are impoverished, display smaller test size, are dominated by a single opportunistic taxon, and have lower numbers of suspension feeders in comparison with assemblages surrounding sediments. In addition, bentonite assemblages show a test composition comprised of white fine-grained quartz, and include a greater number of juvenile forms with test abnormalities. The extent of such discrepancies is variable and depends on the thickness of the bentonite layers. The deposition of volcanic ash layers (bentonites) represented catastrophic events for benthic foraminifera. After each ash fall event a kill layer was formed, and settled by an opportunistic foraminiferal group dominated by specimens of the epifaunal Glomospira charoides, leading to the formation of nearly monospecific foraminiferal assemblages. In the case of thin ash layers some infaunal species are found. These organisms probably survived the deposition of volcanic ash and associated unfavourable conditions beneath the surficial sediment layer. The studied sections of the Subsilesian Unit include intervals containing several bentonite layers, indicating that the deposition of volcanic ash was a recurrent phenomenon. Following the deposition of volcanic ash, a relatively quick recovery of the foraminiferal community structure took place, and changes in the foraminiferal community proceeded each time according to the same sequence.

The effects of soil texture and ash thickness on the post-fire hydrological response from ash-covered soils

Summary Ash increases the post-fire hydrological response to rainfall in some situations but decreases it in others, and the reasons for this variability are not well defined. We used simulated rainfall experiments to determine whether the varying hydrological effect of ash can be attributed to differences in the underlying soil texture or the ash thickness. We compared the infiltration rates: (1) before and after controlled burns in 0.5 m2 plots underlain by two sharply contrasting soil textures (sandy loam and gravelly silt loam), and; (2) before and after the addition of 0.5, 2.5 and 5.0 cm of ash to the burned sandy loam plots with the original ash layer removed. The controlled burns left a ∼1 cm ash layer comprised mostly of silt and fine sand particles that clogged the largest pores in the sandy loam soil, reducing the final infiltration rate from 91 mm h−1 to 35 mm h−1, but had no effect on infiltration in the silt loam plots. Pore clogging also reduced the final infiltration rate by 20 mm h−1 (40%) and the total infiltration by 16 mm (24%) when 0.5 cm of ash was added to the sandy loam plots. However, increased storage in the ash layer combined with slight increases in the final infiltration rate (by 5 and 18 mm h−1, respectively), increased the total infiltration by 16 mm (30%) and 18 mm (26%), respectively with the thicker ash addition treatments. Thus, the varying effect of ash on infiltration and runoff can be at least partially attributed to between-site differences in soil texture and ash thickness. A thin ash layer (

Late Holocene paleopedological records contained in tephra from El Chichón volcano, Chiapas, Mexico

High rates of pedogenesis on unconsolidated volcanic materials imply the accelerated generation of the soil memory. The purpose of this research was to extract the high resolution (centennial scale) paleopedological records from the Late Holocene paleosols of the El Chichón volcano formed during the last 2000 years. We studied buried monogenetic Andosols on the dated tephras and a pedocomplex formed from a set of thin ash layers deposited on older Acrisol derived from shales. Particle size distribution, DCB-extractable Fe, oxalate-extractable Fe, Al and Si, sand and clay mineralogy, organic carbon content and stable C isotope composition in humus were evaluated and interpreted as the elements of the soil memory. However, some differences were found in properties of two buried soils, especially in the kind of A horizons. We attribute such differences of individual Andosols to be caused by ancient human impact because it has been demonstrated that humid conditions persisted during the last 1300 years. Thus the drought that was supposed to provoke the collapse of the Maya civilization at the end of I millennium A.D., should have been a short-term event, below the resolution of this paleopedological record. The Andic Acrisol pedocomplex demonstrated the domination of the humid tropical climate over longer time intervals (probably major part of the Holocene) with possible minor dry episodes.

Influences of urban fabric on pyroclastic density currents at Pompeii (Italy): 2. Temperature of the deposits and hazard implications

During the A.D. 79 eruption of Vesuvius, Italy, the Roman town of Pompeii was covered by 2.5 m of pyroclastic fall pumice and then partially destroyed by pyroclastic density currents (PDCs). Thermal remanent magnetization measurements performed on the lithic and roof tile fragments embedded in the PDC deposits allow us to quantify the variations in the temperature (Tdep) of the deposits within and around Pompeii. These results reveal that the presence of buildings strongly influenced the deposition temperature of the erupted products. The first two currents, which entered Pompeii at a temperature around 300–360°C, show drastic decreases in the Tdep, with minima of 100–140°C, found in the deposits within the town. We interpret these decreases in temperature as being the result of localized interactions between the PDCs and the city structures, which were only able to affect the lower part of the currents. Down flow of Pompeii, the lowermost portion of the PDCs regained its original physical characteristics, emplacing hot deposits once more. The final, dilute PDCs entered a town that was already partially destroyed by the previous currents. These PDCs left thin ash deposits, which mantled the previous ones. The lack of interaction with the urban fabric is indicated by their uniform temperature everywhere. However, the relatively high temperature of the deposits, between 140 and 300°C, indicates that even these distal, thin ash layers, capped by their accretionary lapilli bed, were associated with PDCs that were still hot enough to cause problems for unsheltered people.

Behaviour of concrete-filled steel tubular columns incorporating fly ash

Abstract The subject of this work is to investigate the effect of fly ash on the strength of concrete filled steel tubular columns from 28 to 365 days. A contrast study was carried out on concrete filled steel tubular columns incorporating 10–40 wt% fly ash, and for control Portland cement concrete filled steel tubular columns. The effect of pre-coating the inner surface of steel tubes with a thin layer of fly ash was also studied. Assessments of the concrete mixes were based on the compressive strength and the bond strength. The results show that a lower replacement with fly ash can improve both bond strength and compressive strength, while a higher replacement with fly ash requires a relatively longer time to achieve similar beneficial effects. Pre-coating the inner surface of steel tubes with a thin layer of fly ash can notably improve the bond strength. The microstructure of the interface between concrete and steel tube was also studied by using scanning electron microscopy analyzer.

The Quaternary pyroclastic succession of southeast Tenerife, Canary Islands: explosive eruptions, related caldera subsidence, and sector collapse

A much-revised Quaternary stratigraphy is presented for ignimbrites and pumice fall deposits of the Bandas del Sur, in southern Tenerife. New 40Ar/39Ar data obtained for the Arico, Granadilla, Fasnia, Poris, La Caleta and Abrigo formations are presented, allowing correlation with previously dated offshore marine ashfall layers and volcaniclastic sediments. We also provide a minimum age of 287±7 ka for a major sector collapse event at the Güimar valley. The Bandas del Sur succession includes more than seven widespread ignimbrite sheets that have similar characteristics, including widespread basal Plinian layers, predominantly phonolite composition, ignimbrites with similar extensive geographic distributions, thin condensed veneers with abundant diffuse bedding and complex lateral and vertical grading patterns, lateral gradations into localized massive facies within palaeo-wadis, and widespread lithic breccia layers that probably record caldera-forming eruptions. Each ignimbrite sheet records substantial bypassing of pyroclastic material into the ocean. The succession indicates that Las Cañadas volcano underwent a series of major explosive eruptions, each starting with a Plinian phase followed by emplacement of ignimbrites and thin ash layers, some of co-ignimbrite origin. Several of the ignimbrite sheets are compositionally zoned and contain subordinate mafic pumices and banded pumices indicative of magma mingling immediately prior to eruption. Because passage of each pyroclastic density current was characterized by phases of non-deposition and erosion, the entire course of each eruption is incompletely recorded at any one location, accounting for some previously perceived differences between the units. Because each current passed into the ocean, estimating eruption volumes is virtually impossible. Nevertheless, the consistent widespread distributions and the presence of lithic breccias within most of the ignimbrite sheets suggest that at least seven caldera collapse eruptions are recorded in the Bandas del Sur succession and probably formed a complex, nested collapse structure. Detailed field relationships show that extensive ignimbrite sheets (e.g. the Arico, Poris and La Caleta formations) relate to previously unrecognized caldera collapse events. We envisage that the evolution of the nested Las Cañadas caldera is more complex than previously thought and involved a protracted history of successive ignimbrite-related caldera collapse events, and large sector collapse events, interspersed with edifice-building phases.

Improve the strength of concrete-filled steel tubular columns by the use of fly ash

Concrete-filled steel tubular columns (CFTs) are becoming widely used in engineering. In the present paper, the addition of fly ash and an expansive agent to the concrete of CFTs or a thin layer of fly ash to the interface between steel tube and concrete (CFTFCs) to improve the compressive strength and the bond strength of CFTs was experimentally investigated. The results show that the expansive concrete-filled steel tubular columns (CFETs) have the highest bond strength and compressive strength at the age of 7 days, and CFTFCs have higher bond strength and compressive strength than fly ash concrete-filled steel tubular columns (CFFTs), which in turn are higher than CFTs. However, both bond strength and compressive strength of CFTFCs become the highest at the age of 28 days. The morphology (size and shape) of mineralogy and microstructure of the interface at the age of 28 days were also investigated by using both scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It is shown that the strength improvement of CFTFCs mainly depends on the content of SiO 2 and CaO in the interface, and higher content of SiO 2 and/or lower content of CaO are preferred.