Small Lava Flows Research Articles

Statistical Insights on the Eruptive Activity at Stromboli Volcano (Italy) Recorded from 1879 to 2023

Stromboli is an open-conduit active volcano located in the southern Tyrrhenian Sea and is the easternmost island of the Aeolian Archipelago. It is known as “the lighthouse of the Mediterranean” for its continuous and mild Strombolian-type explosive activity, occurring at the summit craters. Sometimes the volcano undergoes more intense explosions, called “major explosions” if they affect just the summit above 500 m a.s.l. or “paroxysms” if the whole island is threatened. Effusive eruptions are less frequent, normally occurring every 3–5 years, and may be accompanied or preceded by landslides, crater collapses and tsunamis. Given the small size of the island (maximum diameter of 5 km, NE–SW) and the consequent proximity of the inhabited areas to the active craters (maximum distance 2.5 km), it is of paramount importance to use all available information to forecast the volcano’s eruptive activity. The availability of a detailed record of the volcano’s eruptive activity spanning some centuries has prompted evaluations on its possible short-term evolution. The aim of this paper is to present some statistical insights on the eruptive activity at Stromboli using a catalogue dating back to 1879 and reviewed for the events during the last two decades. Our results confirm the recent trend of a significant increase in major explosions, small lava flows and summit crater collapses at the volcano, and might help monitoring research institutions and stakeholders to evaluate volcanic hazards from eruptive activity at this and possibly other open-vent active basaltic volcanoes.

Three-dimensional density tomography determined from multi-directional muography of the Omuroyama scoria cone, Higashi–Izu monogenetic volcano field, Japan

Scoria cone is one of the basic forms of volcanoes, and clarifying its detailed internal structure and magma movement during its formation is important for understanding the nature of eruptions and also for volcanic disaster mitigation. We conducted a multi-directional muographic survey of the Omuroyama scoria cone, Japan, in order to determine the three-dimensional density structure of the scoria cone. We used a nuclear emulsion detector optimized for multi-directional muography that was installed at 11 sites around the volcano. Muon tracks recorded on emulsion films were read with a high-speed automated readout system. We obtained the three-dimensional density structure by applying a linear inversion to the muographic images, and evaluated the uncertainties. High-density zones were detected in scoria cone. Based on these observations and detailed topographic and geological constraints, we infer that high-density zones are the central, highly welded vent of the scoria cone, three-directional radial dikes extending from the central vent, respectively. We also infer that an E-W-trending dike fed a small lava flow, and that a SSE-NNW-trending dike caused a small flank eruption and produced a crater on the flank of the cone. Our results visualize the three-dimensional internal structure of volcanoes with novel resolution, and thereby demonstrate that the formation process of volcanoes can be discussed in detail. Since it has been difficult to directly detect such clear visualization of the internal structures and eruptive processes in the past, multi-directional muography has resulted in providing one hope for understanding volcanic activity.

Tephrostratigraphy and morphometry of Wum Maar Volcano (Oku Volcanic Group- Cameroon Volcanic line): Implications for complex monogenetic volcanoes

Field investigations of tephra deposits and morphometric characterisation were used to constrain the eruptive history and the complexity of the Wum Maar Volcano (WMV) on the Northwestern foot of the Oku Volcanic Group (Cameroon Volcanic Line). The WMV is a compound volcanic edifice made up of an irregular horse-shoe-shaped maar-crater bordered by overlapping scoria cones and a small lava flow field. The bulk ejecta volume computed using ArcGIS.10.3 and field topographic measurements is ∼0.133 km3. The deposits were subdivided into older volcanics, a pre-maar member composed of four Strombolian scoria cones and a maar-member made up of interbedded layers of lapilli-tephra, lapilli-ash, and ash-breccia deposits. The bedding characteristics (structure, bedding dip, direction, attitude, and contact relations) coupled with the componentry analysis of maar deposits indicate phreatomagmatic-derived fallouts and pyroclastic density currents emplaced under both dry and wet conditions due to variations in magma-water ratio during the different phreatomagmatic explosions. The thick paleosol between older volcanics and the pre-maar and the maar deposits suggests that before the formation of the WMV, an eruptive activity took place and comprised an effusive outpouring of a basaltic magma batch that exploited the network of fractures within the basement rocks to reach the surface. Long after this stage, other batches of basanitic and trachybasaltic magmas richer in volatiles erupted explosively (Strombolian eruptive dynamism) around the northern and southern rims of the maar crater, leading to the emplacement of several overlapping scoria cones. The last stage was characterised by the formation of the Wum maar crater through a phreatomagmatic explosion when batches of basanitic magma came in contact with groundwater. The volcanics are sub-aphyric and host mantle xenoliths. Although evenly distributed across the different maar units, these mantle xenoliths are frequent and large enough to suggest a rapid magma ascent. The center of the maar crater compared to the location of the scoria cones suggest that the explosion locus migrated eastwards. The relative proportion of lithic granite within the pyroclastic succession increases upward (highest in MU4), and the depth of the maar varies from <10 m at the western border to about 124 m at the eastern one, suggesting a vertical and a lateral migration of the explosion locus. The intensity of the phreatomagmatic explosion reduced with time as indicated by the clast-size distribution, with a progressive reduction in water availability wherein the eruption became more internally controlled, changing in style from phreatomagmatic to Strombolian at the end. We conclude that even with very small magma volumes, monogenetic eruptions can have very complex histories, as shown by the WMV, because of the taping system, multiple vents, change in eruptive style, vertical and lateral migration of eruption foci, and multiple magma batches.

Global Volume Distribution for Subaerial Volcanism on Earth

AbstractKnowledge of the global distribution of Earth volcanism is critical in many fields of the Geosciences involving large‐scale assessments, such as plate tectonics, global volcanic hazards, and climate change. Recent analysis has revealed that global eruption inter‐event times are exponentially distributed, implying that on the global scale volcanic eruptions are Poisson distributed. Here, we employ those findings to calibrate a continuous frequency‐volume distribution for subaerial eruptions of any size on Earth from small lava flows to super‐eruptions. Obtaining such a continuous global distribution implies considering the existing data and the way they are collected and categorized into databases, as well as extending the available eruption volume data to eruption VEI classes less than 4. The continuous global distribution shows an initial log‐normal section up to volumes of about 170 Mm3, followed by a power‐law section, tapered on its extreme right‐end side, encompassing about five orders of magnitude of eruption volumes. The potential implications are discussed in terms of short‐term eruption forecasts of the size of an impending eruption, critical for volcanic emergency management.

The pyroclastic breccias from Cabezo Negro de Tallante (SE Spain): Is there any relation with carbonatitic magmatism?

The small Plio-Quaternary volcanic centre of Cabezo Negro de Tallante in SE Spain includes a thick deposit of polymictic pyroclastic tuff-breccia, whose fragments are agglutinated by a carbonate-rich component. This feature is also observed in other monogenetic volcanic centres cropping out in the Tallante-Cartagena volcanic district. The carbonate fraction has been recently interpreted in literature as representing a mantle component, therefore pointing to the existence of a diffuse carbonatitic activity in the area.Based on detailed sedimentological (presence of pisoids and root remnants), petrographic (presence of plagioclase and absence of euhedral silicate minerals in the calcite plagues), mineral chemistry (Ba-Sr-poor calcite composition), whole-rock chemistry (overall low incompatible element content in the pure carbonate fraction and a monotonous trace element negative correlation with CaO) as well as isotopic constraints (perfect correlations between Sr-Nd-Pb isotopic ratios with CaO in the basaltic and carbonate fraction, as well as heavy δ18O and light δ13C isotopic composition of the carbonate fraction), we propose a secondary origin for the carbonate component, excluding any contribution of mantle carbonatite melts. The presence of carbonates infiltrating the abundant mantle and crustal xenolith fragments found in the pyroclastic breccia is not related to the presence of carbonatitic melts at mantle to lower crustal depths, but to in-situ fragmentation of the Strombolian tuff-breccia deposit, followed by secondary carbonate infiltration. The pyroclastic breccia was indeed affected by an alternation of carbonate precipitation and dissolution in a vadose zone, where the activity of bacteria, fungi, roots and meteoric water led to the formation of a calcrete (caliche)-type deposits.Basaltic rocks (hawaiites and basanites) occur in the area as scoria and lava fragments in the pyroclastic breccia as well as small lava flows. They have been modelled with a low-degree partial melting of an amphibole-bearing peridotitic mantle close to the lithosphere-asthenosphere boundary. The origin of the mildly alkaline sodic basaltic activity in SE Spain post-dates the abundant and long-lasting subduction-related volcanic phase in the Betic Chain. Its origin is explained without requiring the presence of any thermal anomaly, but simply as consequence of the difference of lithospheric depths and edge-driven-type small-scale convection.

КОМПЛЕКСНЫЕ ГЕОЛОГО-ГЕОФИЗИЧЕСКИЕ ИССЛЕДОВАНИЯ ПОДВОДНОГО ВУЛКАНА 7.10 (КУРИЛЬСКАЯ ОСТРОВНАЯ ДУГА)

Submarine volcano 7.10, which is part of the North Iturup group of submarine volcanoes of the Kuril island arc, was studied in 5 voyages of the research vessel Vulkanolog in 1982–1989. Comprehensive studies have shown that the edifice of the 7.10 submarine volcano is composed of rocks of a range from dacites to basalts. The summit and slopes of the volcano are devoid of sediments, and the base is overlain by a sedimentary stratum, thickness of which reaches 800 m. The minimum depth recorded above the top of the volcano is 210 m. In the volcanic edifice, subvertical, northeastern and northwestern feeder channels, as well as peripheral magma chambers at depths of 2.5–3.0 km, were identified. It is assumed that during the terminal eruption, small lava flows poured out in the northeast and southwest directions, while the main lava flow poured out in the southeast direction and reached the base of the volcanic edifice.

Eruption history and petrogenesis of rocks from Nyos volcano (NW Cameroon): Evidence from lithostratigraphy and geochemistry

Even though ca 1746 people and over 3000 cattle were killed in 1986 by sudden release of about 800 million m3 of CO2 from Lake Nyos volcano in northwest Cameroon, the lake's formation history is not known. Here we report results of a lithostratigraphic and petrogenetic study of Nyos volcano that allows us to confirm its phreatomagmatic (maar) origin. Eruptive products are divided into 2 units, the phases of each of which are closely related in time. Unit A comprises 4 phases, the last (A-4) represents the cataclysmic phreatomagmatic formation of Nyos maar and may have been triggered by collapse of the vent system of the previous (A-1 to A-3) phases, and/or reactivation of basement faults. After a repose period, activity shifted NE of the maar to form Unit B products. The B-1 phase of this unit deposited the scoria now covering most of the Lake Nyos area. Unit B-2 constructed the Fon's cone. A small lava flow (Unit B-3) represents the latest phase of volcanic activity of Nyos volcano. Based on area-thickness estimation methods, a total of ca 0.8 km3 of eruptive material was produced from the volcano. Geochemical data suggest that magma of the 2 units probably formed by melting of the same garnet-bearing OIB-like asthenospheric mantle source, and evolved mainly by crustal contamination and fractional crystallization in independent magma batches that erupted without mixing. Our results provide a basis for advice on general hazard mitigation in the Lake Nyos area.

Quantifying Effusion Rates at Active Volcanoes through Integrated Time-Lapse Laser Scanning and Photography

During volcanic eruptions, measurements of the rate at which magma is erupted underpin hazard assessments. For eruptions dominated by the effusion of lava, estimates are often made using satellite data; here, in a case study at Mount Etna (Sicily), we make the first measurements based on terrestrial laser scanning (TLS), and we also include explosive products. During the study period (17–21 July 2012), regular Strombolian explosions were occurring within the Bocca Nuova crater, producing a ~50 m-high scoria cone and a small lava flow field. TLS surveys over multi-day intervals determined a mean cone growth rate (effusive and explosive products) of ~0.24 m3·s−1. Differences between 0.3-m resolution DEMs acquired at 10-minute intervals captured the evolution of a breakout lava flow lobe advancing at 0.01–0.03 m3·s−1. Partial occlusion within the crater prevented similar measurement of the main flow, but integrating TLS data with time-lapse imagery enabled lava viscosity (7.4 × 105 Pa·s) to be derived from surface velocities and, hence, a flux of 0.11 m3·s−1 to be calculated. Total dense rock equivalent magma discharge estimates are ~0.1–0.2 m3·s−1 over the measurement period and suggest that simultaneous estimates from satellite data are somewhat overestimated. Our results support the use of integrated TLS and time-lapse photography for ground-truthing space-based measurements and highlight the value of interactive image analysis when automated approaches, such as particle image velocimetry (PIV), fail.

Petrogenesis of the Neogene bimodal magmatism of the Galatean Volcanic Province, Central Anatolia, Turkey

A series of geochemical analyses and radiometric age determinations are undertaken on rock samples collected from the Çamlıdere region in the Galatean Volcanic Province of NW Turkey, to better understand the characteristics of the bimodal Early–Middle Miocene volcanism developed near the Late Cretaceous Tethyan Suture Zone. Çamlıdere volcanic rocks consist of large volumes of older (>20Ma) calc-alkaline andesites, dacites and rhyolites and pyroclastites, and small volumes of slightly younger (~19Ma) alkaline trachybasalts and basaltic trachyandesites, cropping out as dykes or small lava flows. The older rocks exhibit elevated LILE, LREE and depleted HFSE contents, carrying geochemical characteristics suggesting earlier subduction process. Some samples of the younger mildly alkaline lavas display geochemical characteristics of intraplate magmatism with enrichment of LILE contents with little or no HFSE depletion. Knowing that the Galatean volcanic rocks experienced syn-volcanic extensional tectonics during the Miocene, we think that the reactivation of the old suture zone produced first calc-alkaline series originated from a subduction-modified subcontinental lithospheric mantle, followed by more alkaline products. However, some volcanic rocks suggest penetration of small amounts of asthenospheric melts to this lithospheric mantle source. The regionally known last volcanic phase produced small amounts of alkaline basaltic rocks in Güvem area at about 10Ma. Volcanic activities ended possibly with, or just after the Güvem event, when the extensional tectonic regime switched to strike-slip faulting in the region, with the inception of one of the major faults of Turkey, the North Anatolian Fault Zone.

Relationship of Mediterranean type lamproites to large shoshonite volcanoes, Miocene of Lesbos, NE Aegean Sea

Shoshonites, which are high-K trachyandesitic rocks, are found in many orogenic belts and are commonly of post-collisional origin. The petrogenesis of shoshonites has been widely debated. Small lava flows and dykes of lamproite and related lamproitic rocks of early Miocene age in Lesbos are coeval with voluminous shoshonite volcanoes. Their distinctive petrology and isotope geochemistry provide an exceptional opportunity to assess the petrogenetic relationship between lamproites and shoshonites. The lamproitic rocks contain phenocrysts of forsteritic olivine (as high as Fo93) and clinopyroxene, both with inclusions of chrome spinel (Cr# ~0.9 or ~0.6) and carbonate melt inclusions, indicating the presence of carbonatite melts. Some complexly zoned clinopyroxene from lamproitic rocks have salite cores with chemical composition suggesting they formed in the upper mantle in a melt strongly enriched in LILE and LREE. Both lamproites and shoshonites show continuous trends of trace elements and their isotopic compositions overlap. Lack of variation in K with Mg# or SiO2 for particular temporal–spatial groups of shoshonites suggests derivation from particular inhomogeneous mantle rather than fractionation processes. In contrast to other peri-Mediterranean lamproites, the Lesbos lamproites and shoshonites have unusual Pb isotope composition that requires a common origin from subcontinental lithospheric mantle enriched in LILE in the Paleozoic. This enrichment process involved partial melting of subducted carbonate-bearing pelites. Triassic rift-related volcanism and formation of Jurassic small ocean basins produced extreme depletion of parts of the mantle. Lamproitic magma was derived from melting of enriched refractory harzburgite, whereas enriched lherzolite, wehrlite and pyroxenite partially melted to supply larger volumes of shoshonitic and related magmas. The NE Aegean Miocene shoshonite province is thus not directly related to contemporary subduction, but may have been triggered by related back-arc extension.

The Mt. Moio eruption (Etna): Stratigraphy, petrochemistry and 40Ar/39Ar age determination with inferences on the relationship between structural setting and magma intrusion

Mt. Moio is the most peripheral scoria cone of Etna volcano and rises above the Peloritani Mountains sedimentary basement, 18km north of the volcano summit.Geological and tephrostratigraphic studies and 40Ar/39Ar age determinations were used to characterize the eruption and constrain its occurrence to ~29ka ago, during the activity of the Ellittico volcano, the volcanic edifice active before the actual one, the Mongibello volcano.The Mt. Moio eruption formed a large scoria cone and a widespread tephra fallout deposit, indicating that vigorous explosive activity produced an eruptive plume; minor effusive activity produced a small lava flow at the end of the eruption. Geochemical data indicate that the composition of erupted magma became less evolved during the eruption (mugearite→basalt–hawaiite); thus Mt. Moio deposits have been divided into Lower and Upper Sequences characterized by similar depositional facies. Based on the classification of Etna flank eruptions available in the literature, Mt. Moio can be classed as an eccentric (sensu Rittmann) and Class B eruption. Historic flank eruptions (e.g. 1669, 1763, 2001, 2002–03) formed deposits that are petrochemically and stratigraphically similar to those of Mt. Moio. The general trend of the Mt. Moio eruptive fissure corresponds to that of extensional neotectonic lineaments in the Apenninic–Maghrebian Chain, indicating that the structure of the basement played a role in controlling the ascent of the volatile-rich magma during Ellittico volcano activity.

Unique event plumes from a 2008 eruption on the Northeast Lau Spreading Center

The creation of ocean crust by lava eruptions is a fundamental Earth process, involving immediate and immense transfers of heat and chemicals from crust to ocean. This transfer creates event plumes (“megaplumes”), massive ellipsoidal eddies with distinctive and consistent chemical signatures. Here we report the discovery of unique event plumes associated with a 2008 eruption on the Northeast Lau Spreading Center. Instead of a large plume hundreds of meters thick, we detected at least eight individual plumes, each ∼50 m thick and apparently only 1–3 km in diameter, yet still rising 200–1000 m above the eruption site. Low and uniform 3He/heat (0.041 × 10−17 mol/J) and dissolved Mn/heat (0.04 nmol/J) ratios in water samples were diagnostic of event plumes. High H2 concentrations (up to 9123 nM) and basalt shards confirmed extensive interactions between molten lava and event plume source fluids. Remote vehicle observations in 2009 mapped a new, small (1.5–5.8 × 106 m3) lava flow. Our results suggest that event plumes are more variable, and thus perhaps more common, than previously recognized. Small event plumes may be preferentially associated with small or sheet-flow eruptions, and massive event plumes with slowly extruding pillow mounds 25–75 m thick. Despite this correlation, and high H2 concentrations, existing theory and seafloor observations argue that cooling lava cannot transfer heat fast enough to create the buoyancy flux required for event plumes. The creation of event plumes under a broad range of eruption conditions provides new constraints for any theory of their formation.

Seismological monitoring of the February 2007 effusive eruption of the Stromboli volcano

On February 27, 2007, the Stromboli volcano, which has usually been characterized by moderate explosive activity, started an effusive eruption with a small lava flow down the NW flank. The permanent broadband network installed on the island allowed the revealing of anomalies in the seismicity before the effusive eruption and for the phenomena to be followed over time, thus obtaining meaningful information about the eruption dynamics. During the effusive phase, a major explosion occurred on March 15, 2007. On that occasion, two strainmeters deployed on the volcano in the previous year recorded a strain increment before the blast. After this explosion, which further destabilized the upper part of the edifice, swarms of Long-Period (LP) and hybrid events were recorded. The characteristics and locations of these events suggest that they were associated with the fracturing processes that affected the summit area of the cone. During the effusive phase, changes in the Very Long Period (VLP) event location were recorded. This type of events accompanied the change in the eruptive style, providing information about the magmatic conduit involved in their seismogenetic processes. The effusive phase stopped on April 2, 2007, and the typical Strombolian activity restarted some months later.

Long-term forecast of eruption style and size at Campi Flegrei caldera (Italy)

The Campi Flegrei caldera is an active and restless volcano in the densely inhabited Neapolitan area of southern Italy. Because of the very high value (lives, properties, infrastructures, etc.) exposed to potential volcanic hazards, it is one of the areas at highest volcanic risk on Earth. In such a situation we have made an attempt to contribute to assessment of its volcanic hazards by providing a quantitative probabilistic long-term forecast of style and size of the next eruption. We have evaluated the most relevant physical parameters of the 22 explosive eruptions of the Campi Flegrei caldera over the past 5 ka. This time span has been taken as the reference period for volcanic hazards assessment on the basis of the volcanic and deformation history of the caldera. The evaluated parameters include dispersal, volume and density of the pyroclastic deposits, volume of erupted magma, total erupted mass, and eruption magnitude. The obtained results permit a size classification of the explosive eruptions, which are grouped into three sizes: small, medium, and large. On the basis of the reconstructed eruption dynamics, we have considered a type event(s) representative of each size class and hypothesized the style of the next event. An effusive eruption will likely generate a dome or very small lava flows, while an explosive event of any size very probably will produce particles fallout and flowage of pyroclastic density currents. Using a Bayesian inference procedure, we have assigned a conditional probability of occurrence to each of the eruption size classes. A small-size explosive eruption is the most likely event with a probability of about 60%; a large-size explosive eruption is the least likely event with a probability of about 4%; a medium-size explosive eruption has a probability of occurrence of about 25%; an effusive eruption has about 11% probability of occurrence.

Transition from Ultrapotassic Kamafugitic to Sub-alkaline Magmas: Sr, Nd, and Pb Isotope, Trace Element and 40Ar–39Ar Age Data from the Middle Latin Valley Volcanic Field, Roman Magmatic Province, Central Italy

The Middle Latin Valley volcanic field forms part of the Roman Magmatic Province and includes Pleistocene monogenetic volcanism characterized by the emplacement of small lava flows and minor pyroclastic ejecta and flows.The absence of a main volcanic edifice and of a large, shallow-level magma reservoir allows the eruption of primitive magmas. Geochemical and petrological data suggest that at least four types of mafic parental magmas are present within the volcanic field: (1) melilite-bearing ultrapotassic (kamafugitic); (2) plagioclase-bearing and -free leucititic (HKS); (3) shoshonitic; (4) sub-alkaline. Ar^Ar dating reveals diachronous emplacement of mafic magmas with different levels of K enrichment; the kamafugitic lavas are the oldest and the sub-alkaline lavas the youngest. Incompatible trace element contents strictly follow K2O, but overall the groups of rocks show similar trace element fractionation, with high field strength elements less enriched than large ion lithophile elements. Despite a restricted range in MgO and SiO2 contents, the Middle LatinValley volcanic rocks have highly variable Sr, Nd and Pb isotopic compositions. The sub-alkaline rocks have the lowest Sr/Sr and the highest Nd/Nd, whereas the kamafugitic rocks have the highest Sr/Sr and the lowest Nd/Nd. Intermediate isotopic compositions between these two end-members are shown by leucitites^plagio-leucitites and shoshonites. A clear, time-dependent trend of isotopic variation is observed. This also holds true for Pb isotope compositions, with shoshonitic and subalkaline rocks showing the most radiogenic signatures and the kamafugitic rocks the least radiogenic signatures.The overall geochemical characteristics of the magmas can be reconciled in terms of a model involving recycling of marly shales within the upper mantle; this overprinted earlier pervasive metasomatism related to melts (supercritical fluids) derived from altered oceanic basalts. The crustal derived (marl) end-member is considered to have been concentrated within a metasomatic vein network within the lithosphere, whereas the supercritical fluid-metasomatized end-member occurs within the surrounding mantle. Early partial melting of veins produced strongly undersaturated melilite-bearing ultrapotassic magma (kamafugitic).The progressive exhaustion of the veined mantle increased the

The morphologies of volcanic landforms at Central Elysium Planitia: Evidence for recent and fluid lavas on Mars

This paper focuses on physical parameters (flow rates and rheological properties) of lava flows observed in the Central Elysium Planitia (CEP) region of Mars. The flows are modeled as Newtonian fluids, using the Jeffrey's equation and the concept of Graetz number, or alternatively as Bingham fluids. In addition to these approaches, a theoretical model of the shape of shield volcanoes based on the solution for the porous flow of an unconfined aquifer is applied to 5 shields, providing independent quantifications of rheological variations between the shields. This analysis indicates that of the five volcanoes studied, two are partially buried by lava postdating their formation, a result which has been confirmed independently in one case by high resolution images. Our observations reveal that two types of lava flows may be found in the CEP region. The first group is composed of large lava flows with viscosities around ∼ 2.5 × 10 5 Pa s or yield strengths ranging from 100 to 500 Pa. The second group includes small lava flows of the shield volcanoes and large leveed lava channels on the plains with viscosities below 10 3 Pa s, or yield strengths less than 200 Pa. When compared with other volcanic regions on Mars investigated with similar approaches, these latter values are, at present, the lowest inferred for martian lava flows. Several hypotheses for the formation of these lavas are discussed in the context of CEP given that low viscosity can be the result of (1) high temperature, (2) low crystal content, (3) low Si abundance of the liquid phase, and/or (4) the presence of dissolved volatiles. Two scenarios are considered. In the first one, it is demonstrated that low viscosity lavas (of low silica content) can be produced in the context proposed by Schumacher and Breuer [Schumacher, S., Breuer, D., 2007. Geophys. Res. Lett. 34. L12202] for recent volcanism. However, geochemical maps derived from GRS measurements do not provide support for anomalously low silica concentrations in this region. In the second scenario, a water-rich magma is proposed, although arguments in favor of a water-rich mantle source below the CEP are not available at the present time.

Satellite measurements of recent volcanic activity at Oldoinyo Lengai, Tanzania

Oldoinyo Lengai (OL) is the only active volcano in the world that produces natrocarbonatite lava. These carbonate-rich lavas are unique in that they have relatively low temperatures (495–590 °C) and very low viscosity. OL has been erupting intermittently since 1983, mostly with small lava flows, pools and spatter cones (hornitos) confined to the summit crater. Explosive, ash-producing eruptions are rare, however, on September 4, 2007 the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) captured the first satellite image of an ash plume erupting from OL, which may be indicative of a new phase of more silica-rich products and explosive activity that has not occurred since 1966–1967. In the months prior to the eruption, thermal infrared (TIR) satellite monitoring detected an increasing number of thermal anomalies around OL. Data from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor analyzed with the MODLEN algorithm detected more than 30 hot spots in the last week of August and first week of September 2007, some of which were from bush fires ignited by lava flows or spatter around the volcano. Higher-resolution ASTER data confirmed the location of these burn scars associated with lava flows. ASTER also detected the appearance of an anomalous hot spot at the summit of OL in mid-June with temperatures ~ 440 °C, the presence of several new lava flows in the crater in July and August, and on September 4 measured higher temperatures (~ 550 °C) possibly suggesting a more silicate-rich eruption. ASTER spectral emissivity data were interpreted to indicate a mixture of carbonate and silicate ash in the eruption plume from September 4. Based on the analysis of both ASTER and MODIS data combined with occasional field observations, there appear to have been 2 distinct eruptive events so far in 2007: a typical natrocarbonatite eruption confined to the summit crater in June–July, and a more intense eruption in August–September consisting of natrocarbonatite lava overflowing the crater and explosive events forming ash plumes up to ~ 5 km high, apparently consisting of a mixture of silicate and carbonate ash. OL is one of the many volcanoes in the world, and especially Africa, that is not regularly monitored with in situ instruments. Continued satellite monitoring along with studies of past thermal activity will help determine how future eruptions and ensuing hazards may be forecasted.

Surface cooling, advection and the development of different surface textures on active lavas on Kilauea, Hawai'i

The validity of lava flow cooling models were investigated using data from a high resolution, high frame rate thermal imaging camera on Kilauea, Hawai'i during August 2004. Once the surface temperature data for small lava flow and lobes were corrected for emissivity, viewing distance, humidity and viewing angle, it was clear that their upper surfaces were thermally stratified on eruption. The interior of a stationary lava lobe was exposed by removing the crust, and its cooling rate was measured at 30 Hz. For this flow, the measured cooling trend was successfully modelled using a finite difference cooling model. However, modelled and measured cooling rates of a pahoehoe lobe and a small channelised lava flow were only in agreement until the crust began to deform. The departure from the modelled trend at this point is attributed to two factors. One is the complex cooling regime of a highly deformed ropy crust in which exposed lava at the crests of the ropes radiates in all directions compared with lava in the troughs where radiative cooling is less effective. The second, and more important, reason for the difference is the reduced flow rate of the crust once it begins to be compressed. The underlying visco-elastic zone beneath the crust flows more rapidly than the crust and consequently advective heat flow significantly reduces cooling rates. Variations in heat loss from different flow textures and the incorporation of different advective heat components is clearly important in future flow models. One of the critical parameters in such models is the temperature at which different surface textures develop. Temperature profiles along lobes and flows also revealed that rope textures developed on pahoehoe lavas when temperatures were in the range of 700–800 °C, brittle deformation of pahoehoe crust occurred when temperature dropped below 700 °C, and small pahoehoe lobes stopped advancing at temperatures of ~ 600–650 °C. It is important to recognise that the flow front temperatures at which these flows stop advancing will be significantly greater than for larger flows on similar gradients. The higher internal and basal shear stresses of large lava flows will allow the flow to advance until the visco-elastic layer at the front of a front is significantly cooler than the temperatures recorded on these small flows on Kilauea.

Possible evidence for on-going volcanism on Mars as suggested by thin, elliptical sheets of low-albedo particulate material around pits and fissures close to Cerberus Fossae

We describe 100–200 metre-sized low-albedo haloes from Mars Orbiter Camera (MOC) images, located around sunken pits in the vicinity of Cerberus Fossae, Mars, a fissure-vent system that has been suggested to have been volcanically active within the last few million years. Two types of pit have been identified: (1) lenticular/elongate pits located on the floors of fissures/graben, some of which lead to the summit of a volcano; (2) sub-circular pits, lacking the raised rims expected of impact craters, located either within small lava flows, along fissures, or on flat, cratered plains. The low-albedo haloes encircle the pits, and are in places asymmetric in plan-view, exhibiting almost perfect elliptical outlines with low-aspect ratios, and lightening in appearance towards the margins of the ellipses. Thermal Emission Imaging System (THEMIS) images suggest the haloes are dark particulate deposits. These deposits bury impact craters to a depth of less than a few decimetres. We argue that the elliptical haloes may be mineral precipitates and/or particulate deposits from ballistic volcanic eruptions that have been disrupted by the wind. They are likely be extremely young because <1m thick, low-albedo sedimentary deposits elsewhere on Mars have been observed to disappear in a few tens of years due to deposition of high-albedo dust.

Blocky versus fluidal peperite textures developed in volcanic conduits, vents and crater lakes of phreatomagmatic volcanoes in Mio/Pliocene volcanic fields of Western Hungary

Volcanic fields in the Pannonian Basin, Western Hungary, comprise several Mio/Pliocene volcaniclastic successions that are penetrated by numerous mafic intrusions. Peperite formed where intrusive and extrusive basaltic magma mingled with tuff, lapilli-tuff, and non-volcanic siliciclastic sediments within vent zones. Peperite is more common in the Pannonian Basin than generally realised and may be also important in other settings where sediment sequences accumulate during active volcanism. Hajagos-hegy, an erosional remnant of a maar volcano, was subsequently occupied by a lava lake that interacted with unconsolidated sediments in the maar basin and formed both blocky and globular peperite. Similar peperite developed in Kissomlyó, a small tuff ring remnant, where dykes invaded lake sediments that formed within a tuff ring. Lava foot peperite from both Hajagos-hegy and Kissomlyó were formed when small lava flows travelled over wet sediments in craters of phreatomagmatic volcanoes. At Ság-hegy, a large phreatomagmatic volcanic complex, peperite formed along the margin of a coherent intrusion. All peperite in this study could be described as globular or blocky peperite. Globular and blocky types in the studied fields occur together regardless of the host sediment.