Pumice Layer Research Articles

Mechanical and hydraulic properties of unsaturated layered pyroclastic ashes in landslide-prone areas of Campania (Italy)

Air-fall pyroclastic soil deposits usually display a loose fabric composed of alternating layers of ashes and pumices. Such deposits, when lying on steep slopes, represent a major geohazard due to the occurrence of landslides. This is the case of the carbonate massifs in Campania (southern Italy), a wide landslide-prone area of approximately 400 km2 covered with pyroclastic soils. In such cohesionless deposits, the additional shear strength provided by soil suction in unsaturated conditions is important for ensuring slope stability and can be jeopardized by soil wetting during rainwater infiltration. This paper provides a comprehensive view of the hydraulic and shear strength characteristics of different layers of pyroclastic deposits at different sites in Campania, revealing a broad view of their similarities and differences. To that end, some datasets from previous studies and novel data are gathered, linking the index properties, the hydraulic behavior of the soils and the contribution of suction to the shear strength of the studied materials. Two types of ashes at different positions within the stratigraphic sequence are identified: ashes interbedded between pumice layers, where landslide failure surfaces usually occur, and altered ashes in contact with the bedrock, which affects water leakage from the overlying soil profile. The former show quite uniform characteristics, and this allowed testing some predictive models for the assessment of the unsaturated shear strength of pyroclastic ashes in the absence of direct measurements. In contrast, the latter may exhibit significantly different behaviors, with great variability in hydraulic and mechanical properties.

Reconstructing the Belbaşhanı Pumice Plinian eruption, Hasandağ Volcano, Turkey

Hasandağ volcano (Central Anatolia, Turkey) has recently underwent an increase in local seismicity and fumarolic activity since 2013. In the past, this volcano has produced multiple large explosive eruptions during the last million years. The Belbaşhanı Pumice is the product of a sub-Plinian to Plinian eruption dated at ~ 417 ± 20.5 ka (40Ar/39Ar). Here, we present a complete volcanological study including stratigraphy, glass chemistry, pumice morphology, geochronology, and eruption source parameters with the associated uncertainties, to characterize the Belbaşhanı Pumice eruption. The eruption involved a column of 18–29 km in height, with the main dispersal axis towards the northeast. A pumice layer up to ~ 17-m-thick accumulated in proximal deposits along the Belbaşhanı path, and up to 2-m-thick in medial-distal areas (~ 18 km northeast from the vent). The high and tubular vesicularity of the pumice clasts indicates that the Belbaşhanı eruption was predominantly magmatic. The bulk volume of the Belbaşhanı Pumice fallout deposit has been estimated as 0.5 and 8 km3 (with ~ 2 km3 being the mean value), which corresponds to Volcanic Explosivity Index (VEI) of at least 4 and up to 6. Both isopach and isopleth maps indicate that the volcanic vent may have been located at the intersection of the Tuz Gölü fault and Ulukışla caldera, within the Hasandağ volcanic complex. The glass composition of Belbaşhanı Pumice confirms that the eruption belongs to the Hasandağ magmatic system. The reconstruction of the Belbaşhanı Pumice eruption represents an essential baseline in providing volcanological constraints for further investigations of tephra fallout hazard assessment in Central Anatolia, especially considering that a new Plinian eruption cannot be ruled out at Hasandağ volcano in the future. The chemical and geochronological datasets presented here could aid in refining tephrochronological correlations, with the goal of synchronizing paleoenvironmental and paleoclimatic records alongside archaeological sites.

Long-lived shallow crustal magma reservoirs beneath Ulleung Island volcano (South Korea) and their rejuvenation recorded in zircon

The microanalytical data obtained from zircons collected on Ulleung Island, an emergent peak of a Quaternary alkaline magma system in the southwestern East Sea (Sea of Japan) back-arc basin, provide new insights into the origin of magma, magmatic processes, and the trigger of explosive eruptions. The U-Th ages of zircons extracted from a pumice layer formed during the intense Plinian eruption at ∼11 ka, known as the Ulleung-Oki tephra, show a wide range spanning the pre-eruption equilibrium state (>350 ka) up to the eruption event itself. Zircon grains derived from syenite and gabbro fragments entrained within the tephra yield weighted mean U-Th and U-Pb ages of 34.7 ± 2.3 ka and 1378 ± 22 ka, respectively. Under cathodoluminescence, zircons from the syenite reveal dark, featureless, or oscillatory-zoned cores, containing numerous inclusions of britholite-like Y-rich phases and pyrochlore. These cores are partially or entirely replaced by inclusion-free, brighter domains, suggesting that in situ dissolution and precipitation processes significantly influenced the transformation of zircon. The consistently low δ18O values (5.4–2.6‰) of zircons from Middle Pleistocene trachyte lavas, the Ulleung-Oki tephra, and lithic fragments indicate the persistent presence of shallow crustal magma reservoirs beneath Ulleung Island. These reservoirs have undergone substantial assimilation of hydrothermally altered rocks, with assimilation rates typically around 10–30% and reaching a maximum of approximately 50%. Zircon core-to-rim variations in oxygen isotopic composition, along with textural observations, suggest the rejuvenation of magma reservoirs through the injection of new melt, which likely served as a trigger for the explosive eruptions at Ulleung Island. The similarity in the range of εHf values between the core and rim (+7.4 to −4.3) implies the Hf isotopic consistency of the recharge melt.

Geophysical Based Groundwater Potential Zone Mapping: Perspectives and Inferences from Lisana Area along the Guder River, Western Margin of the Central Main Ethiopian Rift

Vertical electrical soundings and magnetic data were used to map the groundwater aquifer system in the Lisana area along the Guder River, northeast of Hosanna town, near the western margin of the Central Main Ethiopian Rift. The surveys were used to map a potential aquifer zone and investigate the groundwater potential for the current and future development of the resource in the Lisana area. The VES data were used to map the depth of a potential aquifer zone and its distribution over the area. The magnetic survey was used to delineate contacts between lithologic units and geological structures. Two-dimensional magnetic forward modeling and one-dimensional electrical modeling were used to identify fractures and lithological units containing potential groundwater. The magnetic and electrical resistivity modeling indicated that a potential aquifer occurs at a depth range from 115m to 142m. The potential aquifer occurs within weathered and fractured ignimbrite and a pumice layer containing sandy soil. This latter lithological unit is the main water-bearing horizon.

Groundwater Potential Mapping Using Geophysical Techniques: a Case Study in Hosanna Area, Western Margin of The Central Main Ethiopian Rift, Ethiopia

In this study, Vertical Electrical Sounding (VES) and magnetic methods are applied for mapping the groundwater potential and aquifer system in the Gode area, the western margin of Central Main Ethiopian Rift. The VES is used to map the depth to potential aquifer zone of the groundwater and its distribution over the area, whereas, the magnetic survey is applied to delineate contact between lithologic units and geological structures. A total of 12 VES data points and more than 400 magnetic data points at about 10m station intervals along seven profiles are collected, processed and analyzed. Our results from interpretation of the VES data, geoelectric sections, and 2D magnetic modeling results respectively revealed the vertical stratification of the subsurface geoelectric layers and the presence of subsurface weak zones, which control the groundwater flow and storage system where the potential aquifer in the area obtained at a depth range from 45m to 92m. Overall, areas in the neighborhood of four VES points, i.e.VES-2, -3, -10, and -11, show good water-bearing zones in the study area associated with the highly weathered/fractured ignimbrite and pumice layers.

Ash aggregate-rich pyroclastic density currents of the 431 CE Tierra Blanca Joven eruption, Ilopango caldera, El Salvador

The VEI 6, Tierra Blanca Joven pyroclastic sequence (30–90 km3 DRE volume), erupted from Ilopango caldera, El Salvador, in 431 CE, is the product of one of the largest eruptions of the last two millennia. The eruption devastated Central America's Mayan civilization. The eruption began with a short-lived phase of ash and pumice fall deposition and transitioned to a ‘wet’ explosive phase during which pyroclastic density currents flowed >40 km from the caldera. Detailed field and sedimentological analyses are provided for the deposits of ash-aggregate-rich pyroclastic density currents generated during early phases of the eruption. The first phase of pyroclastic density current inundation incinerated forests and deposited up to 30 m of, non-welded, ash-rich ignimbrite in proximal regions, along with ash fall layers of co-ignimbrite origin. Following fallout of a thin layer of pumice and lithic lapilli, a second phase of pyroclastic density current inundation and co-ignimbrite ash fall commenced. A range of ash aggregate types is present in the pyroclastic density current deposits and interbedded co-ignimbrite ash fall layers. Whole and broken concentrically layered ash aggregates (accretionary lapilli) reach >50 vol% in some horizons within some beds in the pyroclastic density current deposits. The evidence indicates that the ash aggregates grew within overriding co-ignimbrite ash plumes and subsequently fell into ground-hugging currents. Our findings suggest that the aggregate-rich nature of the pyroclastic density current deposits originated through incorporation of lake water into eruptive plumes, which in turn triggered rapid, pervasive aggregation within ash clouds and co-ignimbrite plumes.

Effect of elevation and slope orientation on pedogenesis of late Holocene volcanic ash on a tropical high mountain in central Mexico

The influence of climate on pedogenesis is elevation dependent, but little is known on the influence of slope orientation. This investigation focuses on the development of soils formed on Holocene (1100 and 5600 years old) volcanic ash deposits along an elevation gradient from 3000 to 4300 m a.s.l. on a high mountain in central Mexico. Soil profiles were analyzed on both N- and S-facing slopes at 3000, 3400, 3800, 4000 and 4300 m a.s.l. To determine the effect of climate (dependent on elevation and slope orientation) on pedogenetic processes, other factors such as age and type of parent material, landform position, and slope angle were kept constant. Soil temperature was recorded at 10 cm depth at each site for one year. Significant differences in temperature were found along the elevation gradient and between N-facing and S-facing slopes. Selective extractions of Fe, Al, and Si (using dithionite, oxalate, and pyrophosphate) indicate vitric properties on the 1100-year-old tephra (modern soil) throughout the elevation gradient, while the soil formed on the 5600-year-old tephra (buried by the 1100 year-old tephra) shows andic properties. The orientation of slopes has favored two evolutionary trajectories in the 1100-year-old soil: short-range-order minerals dominate on S-facing slopes, and organo-metallic complexes on N-facing slopes. The lower preservation of ash and pumice layers on S-facing slopes suggests that they have experienced geomorphic instability at centennial scales. The pedogenetic and stratigraphic differences observed between N- and S-facing slopes can be extrapolated to similar valleys and volcanic mountains.

Millennial-scale coseismic landslide history inferred from topographic and stratigraphic features of a post-caldera cone of Aso Volcano in southwestern Japan

The 2016 Mw 7.0 Kumamoto earthquake triggered numerous landslides of fallout tephra deposits around Aso Volcano in southwestern Japan. Although rainfall-induced landslides have been repeatedly observed on the tephra-mantled slopes of this region, the spatial patterns and frequency of coseismic landslides remain unclear because of the scarce landslide evidence associated with palaeoseismicity. To examine the distribution of landslides induced by the 2016 Kumamoto earthquake and possibly by prior large earthquakes, we conducted geomorphological analyses using airborne light detection and ranging (LiDAR) data, together with geological investigations of tephra deposits in the Takanoobane lava dome (TLD), a post-caldera cone of Aso Volcano. Repeated LiDAR surveys performed before and after the earthquake allowed us to quantify the volume and geometry of five coseismic landslides (K1–K5), as well as three component blocks of the K1 landslide (K1a–c). The surveys also allowed identification of 12 older landslides (O1–O12) fully covered by vegetation. Source areas of recent coseismic landslides ranged from 1050 to 14,920 m2; those of older landslides were estimated to be 1110–15,730 m2. The H/L ratios of the K1 landslide and its component blocks K1a–c ranged from 0.139 to 0.165, despite their volumes ranging from 104 to 105 m3. The K1 landslide occurred on the southwest-facing slope, where older landslides were not recognised before the earthquake. Its slip surface was formed at the base of the 30 ka pumice layer. The largest one of the older landslides (O1) is located on the south-facing slope, adjacent to the K1 landslide. Stratigraphic investigations revealed that most of the tephra sequence, including the 30 ka pumice layer, has already been eroded at the centre of the O1 landslide. Radiocarbon dating further constrained the landslide age to ca. 7.0 ka. Because its topographic and stratigraphic features are similar to the features of the K1 landslide, the O1 landslide may have been triggered by a palaeoearthquake approximately 7000 years ago, which was previously unknown around the Aso caldera region.

The Mobility of Landslides in Pumice: Insights from a Flume Experiment

Risk of landslide hazards strongly depends on how far landslide sediment travels, known as landslide mobility. Previous studies mentioned enhanced mobility of earthquake-induced landslides in volcanic deposits compared to those from other geologic/soil settings. A flume apparatus constructed at a 1:300 scale was used to examine the mobility of landslides with pumice. Four pumice samples were collected from landslides induced by the 2018 Eastern Iburi earthquake, Hokkaido, Japan. Laboratory tests confirmed the unique low specific gravity of the pumice (1.29–1.33), indicating numerous voids within pumice particles. These voids allowed pumice to absorb a substantial amount of water (95–143%), about 9–15 times higher than other coarse-grained soils. Our flume experiments using various saturation levels (0–1) confirmed the influence of this inner-particle water absorption on pumice mobility. Because a low value of specific gravity indicates a low strength of soil, grain crushing may occur on the pumice layer, causing water from the internal voids to discharge and fluidize the transported landslide mass. Our findings indicate that such earthquake-induced landslides can be as mobile as those induced by rainfall, depending on the initial water content of the pumice layers. These conditions might be associated with water accumulation from previous rainfall events and the water-holding capability on pumice layers.

Curie Temperatures and Emplacement Conditions of Pyroclastic Deposits From Popocatépetl Volcano, Mexico

AbstractMost pyroclastic deposits of Popocatépetl volcano were emplaced at high temperatures and have similar mafic to more evolved compositions, suggesting a long‐lived, interconnected magma environment. We performed a magnetic and microscopic study on different eruptive sequences <14 ky in age and found that temperature and field dependence of magnetic susceptibility are suited to separate eruption phases. We observed homogeneous titanomagnetite with Curie temperatures (TC) of 50–200°C and 200–400°C, together with different amounts of oxy‐exsolved titanomagnetite with TC ∼ 570°C. Some block‐and‐ash flow deposits show remarkably irreversible TC in heating and cooling branches with a positive ΔTC (TC heating–TC cooling) of up to 130°C in the center. The central part of this sequence is characterized by decreasing magnetic susceptibility and low field dependence of magnetic susceptibility (<10%), which is atypical for ulvöspinel‐rich titanomagnetite. The nonreversibility of heating and cooling runs measured with rates of around 10 K/min is probably related to vacancy‐enhanced nanoscale chemical clustering, which seems to occur preferentially during rapid quenching, possibly combined with subtle maghemitization. In contrast, pumice layers have the highest field dependence (∼20%) and contain Ti‐rich and intermediate titanomagnetite with TC < 100 and ∼300°C, which are in line with mafic and more evolved magma composition. In intermediate phases, irreversibility of TC is more common but with a relatively low ΔTC of ±20°C. We suggest that magneto‐mineralogy in pyroclastic density currents is complex but offers a complementary tool to the paleomagnetic directional analysis for emplacement temperature and contribute information on the volcanic material history and their emplacement conditions.

Hydrological monitoring of a slope covered by stratified pyroclastic deposits and analysis of infiltration processes

AbstractIn addition to the duration and intensity of rainfall, infiltration processes are strongly affected by the hydraulic properties of the soil. In the case of heterogeneous and stratified soil profiles, the analysis of the infiltration process becomes more complex, since conflicting hydraulic properties of adjacent layers can induce locally diverted flow. Soils of volcanic origin present these characteristics, because during the various eruptive phases, layers with very different textures are deposited. In this article, data are analysed which have been recorded by a monitoring station installed on a slope made up of volcanic deposits. The station consists of a rain gauge to measure rainfall and seven tensiometers and eight TDR probes installed at different depths to measure suction and volumetric water content, respectively. The slope is made up of alternating volcanic ash (silt‐sandy‐clay paleosoils) interspersed with pumice (sandy‐gravel), due to the different eruptive phases of the volcanic complexes in the area. The analysis of the data established that the layers of coarser material (pumices), depending on the initial moisture conditions, may hinder or even favour the infiltration of water into the deeper layers. In particular, when water content is low, the pumices presented a low unsaturated conductivity which hindered infiltration. By contrast, in wetter conditions, they favoured the flow of water. Therefore, the initial moisture conditions of the soil layers must be taken into account for a correct prediction of the infiltration phenomena. Dry conditions of the pumice layers can hinder drainage into the lower layers, thus favouring the rapid accumulation of soil water during rainfall events, which could eventually lead to slope failure.

Petrochemical characteristics and geological significance of the tephra buried under peat deposits: Constrains on the Changbaishan Millennium eruption

Changbaishan Tianchi volcano is one of the most famous active volcanoes in Northeast Asia. Its Millennium eruption (ME, 946–947 CE) is considered to be one of the largest explosive eruptions over the past 2000 years, which had produced widely distributed tephra layer across Northeast Asia. However, little attention has been paid to the tephra buried in peatlands around this volcano. Here we present petrographic, geochemical and AMS14C data of the volcanic glasses within a new discovered macro-tephra layer buried in the Yueliangwan peatland, northeast China. The results suggest that buried tephra was the product of Changbaishan Millennium eruption. The eruptive sequence of the ME included comendite eruption and trachyte eruption from bottom to top. Tectonic background analyses reveal that Changbaishan Tianchi volcano regions belong to the anorogenic within plate back-arc extensional tectonic environments. Eruptive and sedimentary processes of the buried tephra were postulated as follows: a large amount of volcanic glasses formed through the eruption of trachyte magma that had high contents of rare earth elements (REE) and trace elements (TE). Then, fine grained volcanic glasses were sprayed into the atmosphere and transported to the Yueliangwan areas. The volcanic glasses deposited and formed airborne pumice layer. This buried tephra layer would act as a key isochronous marker horizon for the chronological framework in a range of sedimentary contexts across Northeast Asia. And it provides accurate eruptive sequence of Changbaishan Millennium eruption. This study would attract more attentions on the buried tephra in peatlands around active volcanoes, which would be of significance for the reconstructions of volcanic eruption history.

Aquifer vulnerability in the Coastal Northern Part of Lombok Island Indonesia

Northern part of Lombok island has a unique geological phenomenon of submarine groundwater discharge. Submarine groundwater discharge needs to be conserved for its sustainability. This study asseses groundwater vulnerability for SGD conservation in the northern part of Lombok Island Indonesia. The assessment was conducted using aquifer vulnerability index methods. Vulnerability index value in the study area is high vulnerability index. This vulnerability index is getting higher toward the coast. The layer is tuffaceous pumice layer with a hydraulic conductivity value of 5 m/day. This layer makes the aquifer in the study area very vulnerable to contamination, especially for pollution involving vertical percolation and infiltration. Protective management is needed to prevent groundwater hazard in the research location due to groundwater pollution and heavy pumping. Anthropogenic activity at the study area should be anticipated because of the high index of aquifer susceptibility at the study area.

Recording Santorini’s subterranean landscapes: A noninvasive approach to the investigation of cave use strategies in insular environments

This paper investigates cave use strategies in insular environments, focusing on a case study from Santorini (Thera) island in Greece. The paper has a two-fold aim to propose and test a methodological framework for noninvasive archaeological evaluation of cave sites and to explore the ways that people, not only on Santorini, but also on similar small islands, have engaged with caves through time. Santorini is famous today as a holiday destination; however, a large part of the island’s historic landscape has disappeared. This is due to the Bronze Age volcanic eruption that covered the majority of the island with a thick layer of tuff and pumice, as well as intensive building and agricultural activity in the second half of the twentieth century, all of which have dramatically transformed the island’s natural environment. Today, our accounts of the island’s prehistory come from the extraordinary preservation of the Akrotiri site, and considerable knowledge gained from other locations, about the role that the island played diachronically in the history of the Aegean. We are, however, still missing valuable information about the relationship between the island’s inhabitants and their environment.

Preliminary analysis of some characteristics of coseismic landslides induced by the Hokkaido Iburi-Tobu earthquake (September 5, 2018), Japan

At 18:07 on September 5, 2018 (UTC), a Mw 6.6 earthquake struck the Iburi-Tobu area of Hokkaido, Japan. The Hokkaido Iburi-Tobu (HIT) earthquake is a reverse-slip earthquake with a focal depth of 33.4 km at 42.69°N and 142.07°E. According to the detailed landslide interpretations, there were approximately 7059 landslides induced by this earthquake concentrated in an area of 466 km2. The landslides induced by the HIT earthquake are mostly shallow landslides whose sources are mainly an air-fall pumice layer from the Tarumai volcano, and these landslides exhibit an obvious characteristic of a “low affected area, large landslide area”. The landslide area follows an exponential distribution, and many landslides are composed of multiple subsource areas. There are at least 8778 source areas in the whole landslide area. The landslides present high mobility, and the landslide deposits not only accumulate on the foot but also “flow” down along the gullies, similar to debris flows, despite the gullies being gentle (<6%), which may be related to recent heavy rainfall events. Most landslides occur on gentle hills with an elevation range of 100–250 m, and the landslide height is mainly concentrated between 15 m and 45 m. Major slide directions follow a nearly SSE-NNW direction, and all the landslides occur with PGA (peak ground acceleration) ≥0.5 g.

Controlling role of Ta-d pumice on the coseismic landslides triggered by 2018 Hokkaido Eastern Iburi Earthquake

The 2018 Hokkaido Eastern Iburi Earthquake triggered massive landslides in the pyroclastic fall deposits. Most of them are shallow debris slides. Based on the field reconnaissance, the shallow debris slides were further categorized into three types: steep translational sliding, gentle translational sliding, and mobilization of V-shaped convergent sliding masses. The three types of shallow landslides were investigated in depth through longitudinal sections, vertical stratigraphic sections, and in situ hardness tests. All three types of shallow landslides were found to initiate from the liquefied failure of the weak Ta-d pumice layer and further evolve to the overall mobilization of the superimposed pyroclastic fall deposits along the liquefied sliding zone. To testify the controlling role and to study the shear behavior as well as the anti-liquefaction strength of the weak Ta-d pumice layer, a series of laboratory tests (basic physical tests and triaxial tests) were conducted on the soils around the sliding zone. The test results indicate that the medium sandy Ta-d pumice MS and the fragile Ta-d pumice CS have lower shear resistance and anti-liquefaction strength than other layers and they can be easily liquefied under intense ground motion. One paleosol layer underlying the Ta-d pumice shows low permeability and enables weathering and soil erosion of the Ta-d pumice, resulting in the widespread existence of the fragile and medium sandy pumice layers in Ta-d. In addition, the positive relationship between coseismic landslide density and Ta-d pumice thickness demonstrates the controlling role of the Ta-d on Iburi landslide occurrence from a macro perspective.

Control Measure Effects on the Effluent Quality from Extensive Green Roofs Based on Stabilized Sludge Recycling

Substrate type is an important factor affecting the quality of water deriving from rainfall onto extensively green roofed areas. Here, stabilized sludge was used as the main nutrient component of the substrate combined with biochar and a dual-substrate structure. Five green roof pilot facilities were constructed, and the effect of control measures on effluent quality was analyzed. The results showed that the stabilized sludge dosage was 3%, and the annual average mass concentrations of total nitrogen (TN) and nitrate nitrogen (NO3--N) were 3.27 mg·L-1 and 1.61 mg·L-1. The use of stabilized sludge as a nutrient component under real rainfall and temperature conditions in Shanghai did not cause significant leaching of TN and NO3--N. In order to further improve the quality of the effluent, biochar was used as an amendment measure. As a result, the concentrations of TN and NO3--N in the effluent were decreased to 2.16 mg·L-1 and 1.38 mg·L-1, respectively. Using an adsorption layer of pumice can alleviate the leaching of total phosphorus (TP) and chemical oxygen demand (COD). For the total nitrogen budget of each pilot facility, the retained TN was about 55% of the original TN after one year of operation. Thus, stabilized sludge could be used as a nutrient substrate to meet the long-term requirements of plants. In the substrate with biochar, the retained TN in the substrate and the NO3--N concentration in the effluent was decreased, which was related to the mineralization of organics during dry periods and the enhancement of denitrification during rainfall periods. Stabilized sludge was not a polluting source of N but was a source of P. Using biochar and a dual-substrate structure can effectively reduce the TN and COD load of the tested green roof facilities.

Osadnictwo ma wyspie Thira (Santoryn) od neolitu po późną epokę brązu

This article presents a history of the Thera Island occupation in the Neolithic and Bronze Age. Altogether, 13 settlements and 2 cemeteries have been recorded from this period. The island was inhabited until the Late Bronze Age. The most significant centre on the island was surely the town of Akrotiri. At the beginning of the Late Bronze Age, a large eruption of the Santorini volcano took place which ceased the occupation and covered the almost entire island with a thick layer of pumice.

B1-09 函館市内で掘削された温泉ボーリングに認められる軽石層(火山地質,口頭発表)

B1-09 函館市内で掘削された温泉ボーリングに認められる軽石層(火山地質,口頭発表)

Investigation on rainwater infiltration into layered shallow covers in pyroclastic soils and its effect on slope stability

In recent years, a number of flowslides and debris flows triggered by rainfall affected a wide mountainous area surrounding the Piana Campana (Southern Italy). The involved slopes are covered with unsaturated air-fall layered pyroclastic deposits, which stability is guaranteed by the contribution of suction to shear strength. To understand the mechanisms of infiltration and to assess the soil suction distribution in such layered deposits, infiltration experiments have been carried out in small-scale slopes. The interpretation of the results has been made with the aid of a 2D mathematical model.The results highlight that the presence of coarse-textured unsaturated pumiceous layers, interbedded between finer ashy layers, can delay the wetting front advancement, thus initially confining the infiltration process within the uppermost finer layer. A diversion of the flow from the vertical towards the slope direction occurs when the soil approaches saturation. However, whereas a high hydraulic gradient establishes across pumices, water infiltration into the deepest layer begins, and part of the water crosses the pumices, before the complete saturation of the uppermost soil profile.