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  • Author: Gábor Kereszturi x
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Shallow-seated controls on the evolution of the Upper Pliocene Kopasz-hegy nested monogenetic volcanic chain in the Western Pannonian Basin (Hungary)

Monogenetic, nested volcanic complexes (e.g. Tihany) are common landforms in the Bakony-Balaton Highland Volcanic Field (BBHVF, Hungary), which was active during the Late Miocene up to the Early Pleistocene. These types of monogenetic volcanoes are usually evolved in a slightly different way than their "simple" counterparts. The Kopasz-hegy Volcanic Complex (KVC) is inferred to be a vent complex, which evolved in a relatively complex way as compared to a classical "sensu stricto" monogenetic volcano. The KVC is located in the central part of the BBHVF and is one of the youngest (2.8-2.5 Ma) volcanic erosion remnants of the field. In this study, we carried out volcanic facies analysis of the eruptive products of the KVC in order to determine the possible role of changing magma fragmentation styles and/or vent migration responsible for the formation of this volcano. The evolution of the KVC started with interaction of water-saturated Late Miocene (Pannonian) mud, sand, sandstone with rising basaltic magma triggering phreatomagmatic explosive maar-diatreme forming eruptions. These explosive eruptions in the northern part of the volcanic complex took place in a N-S aligned paleovalley. As groundwater supply was depleted during volcanic activity the eruption style became dominated by more magmatic explosive-fragmentation leading to the formation of a mostly spatter-dominated scoria cone that is capping the basal maar-diatreme deposits. Subsequent vent migration along a few hundred meters long fissure still within the paleovalley caused the opening of the younger phreatomagmatic southern vent adjacent to the already established northern maar. This paper describes how change in eruption styles together with lateral migration of the volcanism forms an amalgamated vent complex.

Abstract

Bondoró Volcanic Complex (shortly Bondoró) is one of the most complex eruption centre of Bakony-Balaton Highland Volcanic Field, which made up from basaltic pyroclastics sequences, a capping confined lava field (~4 km2) and an additional scoria cone. Here we document and describe the main evolutional phases of the Bondoró on the basis of facies analysis, drill core descriptions and geomorphic studies and provide a general model for this complex monogenetic volcano. Based on the distinguished 13 individual volcanic facies, we infer that the eruption history of Bondoró contained several stages including initial phreatomagmatic eruptions, Strombolian-type scoria cones forming as well as effusive phases. The existing and newly obtained K-Ar radiometric data have confirmed that the entire formation of the Bondoró volcano finished at about 2.3 Ma ago, and the time of its onset cannot be older than 3.8 Ma. Still K-Ar ages on neighbouring formations (e.g. Kab-hegy, Agár-teto) do not exclude a long-lasting eruptive period with multiple eruptions and potential rejuvenation of volcanic activity in the same place indicating stable melt production beneath this location. The prolonged volcanic activity and the complex volcanic facies architecture of Bondoró suggest that this volcano is a polycyclic volcano, composed of at least two monogenetic volcanoes formed more or less in the same place, each erupted through distinct, but short lived eruption episodes. The total estimated eruption volume, the volcanic facies characteristics and geomorphology also suggests that Bondoró is rather a small-volume polycyclic basaltic volcano than a polygenetic one and can be interpreted as a nested monogenetic volcanic complex with multiple eruption episodes. It seems that Bondoró is rather a “rule” than an “exception” in regard of its polycyclic nature not only among the volcanoes of the Bakony-Balaton Highland Volcanic Field but also in the Neogene basaltic volcanoes of the Pannonian Basin.

Abstract

Payún Matru Volcanic Field is a Quaternary monogenetic volcanic field that hosts scoria cones with perfect to breached morphologies. Los Morados complex is a group of at least four closely spaced scoria cones (Los Morados main cone and the older Cones A, B, and C). Los Morados main cone was formed by a long lived eruption of months to years. After an initial Hawaiian-style stage, the eruption changed to a normal Strombolian, conebuilding style, forming a cone over 150 metres high on a northward dipping (∼4°) surface. An initial cone gradually grew until a lava flow breached the cone’s base and rafted an estimated 10% of the total volume. A sudden sector collapse initiated a dramatic decompression in the upper part of the feeding conduit and triggered violent a Strombolian style eruptive stage. Subsequently, the eruption became more stable, and changed to a regular Strombolian style that partially rebuilt the cone. A likely increase in magma flux coupled with the gradual growth of a new cone caused another lava flow outbreak at the structurally weakened earlier breach site. For a second time, the unstable flank of the cone was rafted, triggering a second violent Strombolian eruptive stage which was followed by a Hawaiian style lava fountain stage. The lava fountaining was accompanied by a steady outpour of voluminous lava emission accompanied by constant rafting of the cone flank, preventing the healing of the cone. Santa Maria is another scoria cone built on a nearly flat pre-eruption surface. Despite this it went through similar stages as Los Morados main cone, but probably not in as dramatic a manner as Los Morados. In contrast to these examples of large breached cones, volumetrically smaller cones, associated to less extensive lava flows, were able to heal raft/collapse events, due to the smaller magma output and flux rates. Our evidence shows that scoria cone growth is a complex process, and is a consequence of the magma internal parameters (e.g. volatile content, magma flux, recharge, output volume) and external conditions such as inclination of the pre-eruptive surface where they grew and thus gravitational instability.

Abstract

Background:

On rare occasions, elective iatrogenic reduction of a dichorionic twin is performed due to maternal request and in order to improve the perinatal outcome.

Materials and methods:

Nine twin-to-singleton reductions were identified retrospectively at the Feto-maternal Unit, University of Szeged, Hungary, between December 1997 and June 2015. A post-procedure, routine weekly sonographic scan revealed severe oligohydramnios in two out of the nine cases (22.2%) and amnioinfusion was performed in the mid-trimester to prolong gestation. The fetus survived in one case (11.1%) and the pregnancy continued until preterm birth.

Conclusion:

A repeated sonographic follow-up for an early diagnosis of oligohydramnios is feasible to avoid miscarriage after artificial embryo reduction.