Strikingly similar examples of edifice collapse and directed blast are the 18 May 1980 eruption of Mount St. Helens (MSH), Washington, USA, and the 30 March 1956 eruption of Bezymianny Volcano (BZ), ...Kamchatka, Russia. In these cases, flank failures led to near-instantaneous decompression and fragmentation of intra-edifice cryptodome magma, which produced catastrophic, laterally directed blasts. In both instances, the blast products consisted of juvenile material with bimodal density/vesicularity distributions: low- and high-density modes at 1900 and 2400 kg m super(- 3) for BZ, 1600 and 2300 kg m super(- 3) for MSH, although the proportion of high-density material is greater at BZ. Blast materials also exhibit striking variety in groundmass crystallinity (< 40 to > 90 vol.%) despite having fairly uniform pheno-crystallinities, suggesting that degassing-driven groundmass crystallization occurred to varying extents within cryptodome magma at both volcanoes. New bulk-rock H sub(2)O and dD measurements confirm that progressive open-system outgassing occurred prior to both blasts. The correlations between crystallinity, clast density, and bulk H sub(2)O contents suggest that syn-blast magma expansion was modulated both by non-uniform volatile distribution within the cryptodome and rheological controls associated with non-uniform crystal content. Spatial heterogeneities in volatiles and crystallinity within a given cryptodome are attributed to distance from the wallrock margin, which probably correlates with timing of magma injection. The greater proportion of high-density material at BZ is speculatively related to lower blast energy compared with MSH.
The new highly porous aerogel materials based on sodium lignosulfonate and silicon dioxide were obtained using sol-gel technology and supercritical fluid processes. Aerogel samples have a developed ...micro-mesoporous structure and are characterized by a high specific surface area (290–450 m2g-1), an average mesopore size of 18–20 nm, micropores are represented mainly by supermicropores with a width of 1.2–2.8 nm. The total pore volume varies from 1.4 to 2.0 cm3g-1. The SEM analysis show that aerogel nanomaterials are highly structured spherical particles 35–55 nm in size with a cylindrical pore open at both ends. The obtained results are the basis for the subsequent optimization of the conditions for creating new composite materials (sorbents, catalyst carriers and sensor devices).
•The new LSNa/SiO2 nanomaterials based on components of different chemical nature were obtained using sol-gel synthesis.•Specific surface area of LSNa/SiO2 aerogel samples dried under supercritical conditions was in the range of 290–450 m2g-1•LSNa/SiO2 nanomaterials are highly structured spherical particles with a size of 35–55 nm.•Obtained LSNa/SiO2 aerogel materials can be used as sorbents or sensor devices.
We present a broad overview of the 2012–13 flank fissure eruption of Plosky Tolbachik Volcano in the central Kamchatka Peninsula. The eruption lasted more than nine months and produced approximately ...0.55km3 DRE (volume recalculated to a density of 2.8g/cm3) of basaltic trachyandesite magma. The 2012–13 eruption of Tolbachik is one of the most voluminous historical eruptions of mafic magma at subduction related volcanoes globally, and it is the second largest at Kamchatka. The eruption was preceded by five months of elevated seismicity and ground inflation, both of which peaked a day before the eruption commenced on 27 November 2012. The batch of high-Al magma ascended from depths of 5–10km; its apical part contained 54–55wt.% SiO2, and the main body 52–53wt.% SiO2. The eruption started by the opening of a 6km-long radial fissure on the southwestern slope of the volcano that fed multi-vent phreatomagmatic and magmatic explosive activity, as well as intensive effusion of lava with an initial discharge of >440m3/s. After 10days the eruption continued only at the lower part of the fissure, where explosive and effusive activity of Hawaiian–Strombolian type occurred from a lava pond in the crater of the main growing scoria cone. The discharge rate for the nine month long, effusion-dominated eruption gradually declined from 140 to 18m3/s and formed a compound lava field with a total area of ~36km2; the effusive activity evolved from high-discharge channel-fed 'a'a lavas to dominantly low-discharge tube-fed pahoehoe lavas. On 23 August, the effusion of lava ceased and the intra-crater lava pond drained. Weak Strombolian-type explosions continued for several more days on the crater bottom until the end of the eruption around 5 September 2013. Based on a broad array of new data collected during this eruption, we develop a model for the magma storage and transport system of Plosky Tolbachik that links the storage zones of the two main genetically related magma types of the volcano (high-Al and high-Mg basalts) with the clusters of local seismicity. The model explains why precursory seismicity and dynamics of the 2012–13 eruption was drastically different from those of the previous eruption of the volcano in 1975–76.
•The 2012–13 eruption of Tolbachik produced 0.55km3 DRE of basaltic trachyandesite magma.•The 2012–13 eruption is one of the most voluminous historical eruptions of mafic magma at subduction-related volcanoes.•Data on the 2012–13 eruption precursors and dynamics are summarized.•Model for the magma storage and transport system of Tolbachik is presented.•Differences of precursory seismicity associated with eruptions of the high-Al and high-Mg magmas are explained.
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Aim. To identify the key resources, actors and directions of the soft power of the Republic of South Africa.
Methodology. The research is based on systemic, communicative and ...institutional approaches, the principle of historicism, methods of traditional document analysis.
Results. It has been established that the Republic of South Africa is a leader in the promotion of soft-power technologies on the African continent, but their implementation is hampered by internal socio-economic problems. It is concluded that its initiatives at the sites of the African Union, as well as projects in the field of tourism and sports, are of great importance for building the potential of the soft power of Pretoria. It is predicted that the concept of the African Renaissance and the philosophy of Ubuntu can form the basis for strengthening the soft influence of South Africa in the international arena.
Research implication. The conclusions obtained can be useful both for studying the specifics of the soft power of African states as a whole, and for developing a strategy for socio-humanitarian cooperation between the Russian Federation and the Republic of South Africa on a bilateral basis and within the framework of interstate structures.
Observations made during January and April 2013 show that interactions between lava flows and snowpack during the 2012–13 Tolbachik fissure eruption in Kamchatka, Russia, were controlled by different ...styles of emplacement and flow velocities. `A`a lava flows and sheet lava flows generally moved on top of the snowpack with few immediate signs of interaction besides localized steaming. However, lavas melted through underlying snowpack 1–4m thick within 12 to 24h, and melt water flowed episodically from the beneath flows. Pahoehoe lava lobes had lower velocities and locally moved beneath/within the snowpack; even there the snow melting was limited. Snowpack responses were physical, including compressional buckling and doming, and thermal, including partial and complete melting. Maximum lava temperatures were up to 1355K (1082°C; type K thermal probes), and maximum measured meltwater temperatures were 335K (62.7°C). Theoretical estimates for rates of rapid (e.g., radiative) and slower (conductive) snowmelt are consistent with field observations showing that lava advance was fast enough for `a`a and sheet flows to move on top of the snowpack. At least two styles of physical interactions between lava flows and snowpack observed at Tolbachik have not been previously reported: migration of lava flows beneath the snowpack, and localized phreatomagmatic explosions caused by snowpack failure beneath lava. The distinctive morphologies of sub-snowpack lava flows have a high preservation potential and can be used to document snowpack emplacement during eruptions.
•Detailed descriptions of Tolbachik 2012–13 lava–snow behavior•New observations of supra-snow `a`a and sheet lava flows•First detailed observations of sub-snow pahoehoe lava flows•Detailed descriptions of snow response to lava•Descriptions of textures indicative of lava–snow interactions
We describe a new type of secondary rootless phreatomagmatic explosions observed at active lava flows at volcanoes Klyuchevskoy (Russia) and Etna (Italy). The explosions occurred at considerable (up ...to 5
km) distances from primary volcanic vents, generally at steep (15–35°) slopes, and in places where incandescent basaltic or basaltic-andesitic lava propagated over ice/water-saturated substrate. The explosions produced high (up to 7
km) vertical ash/steam-laden clouds as well as pyroclastic flows that traveled up to 2
km downslope. Individual lobes of the pyroclastic flow deposits were up to 2
m thick, had steep lateral margins, and were composed of angular to subrounded bomb-size clasts in a poorly sorted ash–lapilli matrix. Character of the juvenile rock clasts in the pyroclastic flows (poorly vesiculated with chilled and fractured cauliflower outer surfaces) indicated their origin by explosive fragmentation of lava due to contact with external water. Non-juvenile rocks derived from the substrate of the lava flows comprised up to 75% in some of the pyroclastic flow deposits. We suggest a model where gradual heating of a water-saturated substrate under the advancing lava flow elevates pore pressure and thus reduces basal friction (in the case of frozen substrate water is initially formed by thawing of the substrate along the contact with lava). On steep slope this leads to gravitational instability and sliding of a part of the active lava flow and water-saturated substrate. The sliding lava and substrate disintegrate and intermix, triggering explosive “fuel–coolant” type interaction that produces large volume of fine-grained clastic material. Relatively cold steam-laden cloud of the phreatomagmatic explosion has limited capacity to transport upward the produced clastic material, thus part of it descends downslope in the form of pyroclastic flow. Similar explosive events were described for active lava flows of Llaima (Chile), Pavlof (Alaska), and Hekla (Iceland) indicating that this type of explosions and related hazard is common at snow/ice-clad volcanoes and sometimes happens also on fluid-saturated hydrothermally altered slopes.
► New type of rootless secondary phreatomagmatic explosions on lava flows has been described. ► Specific feature of the new type of secondary explosions is generation of pyroclastic flows. ► The explosions occur due to interaction of molten lava with ice/water-saturated substrate. ► Fuel-coolant type interaction of lava and the substrate is facilitated by gravitational sliding.
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