Phreatomagmatic volcanic hazards where rift-systems meet the sea, a study from Ambae Island, Vanuatu

Uncorrected proofAmbae Island is a mafic stratovolcano located in the northern Vanuatu volcanic arc and has a NE–SW rift-controlled elongated shape. Several hundred scoria cones and fissure-fed lava fields occur along its long axis. After many decades of quiescence, Ambae Island erupted on the 28th of November 2005, disrupting the lives of its 10,000 inhabitants. Its activity remained focused at the central (crater-lake filled) vent and this is where hazard-assessments were focused. These assessments initially neglected that maars, tephra cones and rings occur at each tip of the island where the eruptive activity occurred b500 and b300 yr B.P. The products of this explosive phreatomagmatic activity are located where the rift axis meets the sea. At the NE edge of the island five tephra rings occur, each comparable in size to those on the summit of Ambae. Along the NE coastline, a near-continuous cliff section exposes an up to 25 m thick succession of near-vent phreatomagmatic tephra units derived from closely spaced vents. This can be subdivided into two major lithofacies associations. The first association represents when the locus of explosions was below sea level and comprises matrix-supported, massive to weakly stratified beds of coarse ash and lapilli. These are dominant in the lowermost part of the sequence and commonly contain coral fragments, indicating that the loci of explosion were located within a reef or coral sediment near the syn-eruptive shoreline. The second type indicate more stable vent conditions and rapidly repeating explosions of high intensity, producing fine-grained tephra with undulatory bedding and cross-lamination as well as megaripple bedforms. These surge and fall beds are more common in the uppermost part of the succession and form a few-m-thick pile. An older tephra succession of similar character occurs below, and buried trees in growth position, as well as those flattened within base surge beds. This implies that the centre of this eruption was very near the coastline. The processes implied by these deposits are amongst the most violent forms of volcanism on this island. In addition, the lowland and coastal areas affected by these events are the most heavily populated. This circumstance is mirrored on many similar volcanic islands, including the nearby SW Pacific examples of Taveuni (Fiji), Upolu and Savai'i (Samoa), and Ambrym (Vanuatu). These locations are paradoxically often considered safe areas during summit/central-vent eruptions, simply because they are farthest from the 34 central sources of ash-fall and lahar hazard. The observations presented here necessitate a revision of this view

Mio/Pliocén freatomagmás vulkanizmus a Pannon-medencében: átfogó vulkano-szedimentológiai tanulmány = Mio/Pliocene phreatomagmatic volcanism in the Pannonian Basin: an integrated volcanosedimentary study

Az OTKA által támogatott F 43346 pályázat a Pannon-medence Mio/Pliocen freatomagmás vulkanizmusának megértését célozta a 2003-2006 időszakban. A pályázat elsősorban üldekföldtani módszerekkel vizsgálta a freatomagamás folyamatok során keletkezett vulkáni üledékeket. A kutatási program ideje alatt a Pannon-medence nyugati és északi területein található, kis-térfogatú, alapvetően bazaltos magmatizmus nyomán keletkezett robbanásos vulkáni kitörések eredményeként felhalmozódott vulkáni üledékes sorozatok vizsgálatára került sor. A kutatást előkészítő program során elsősorban a nyugat-magyarorszagi területekre koncentrálódott a vizsgálat, majd abbol kiindulva probálta meg a kutatási programot kiterjeszteni a Pannon-medence más területeire is. A kutatás ideje alatt kialakított nemzetközi kapcsolatrendszereknek köszönhetően a kutatási programba számos külföldi kutató is bekapcsolódott, aminek eredményeként sikerült kapcsolatot teremteni a Pannon-medence területén felismert freatomagmás folyamatok és más (Patagonia, Argentína; Dolomitok, Olarszország; Idaho, USA, Transmexican vulkáni övezet, Mexico; DNy-Csendes-óceani szigetvilág) freatomagmás vulkáni vidékein felismerhető vulkáni folyamatokkal. A kutatás során olyan mennyiségű új adatot sikerült gyűjteni a nyugat-magyarországi terültekről, hogy a kutatás fő súlypontja mindvégig e területre esett, így pl. a Nógrád-Gömör területeken a kutatás futamideje alatt csak kezdeti lépéseket sikerült tenni. | The OTKA F 43346 research project (2003-2006) aimed to develop a better understanding of phreatomagmatic processes associated with the Mio/Pliocene alkaline basaltic volcanism in the Pannonian Basin. The research project applied volcano-sedimentological methods to study eruptive products of small-volume, alkaline basaltic phreatomagmatic volcanism. The main research fields of this project was the western and northern side of the Pannonian Basin, where magma-water interaction triggered phreatomagmatic volcanism was common. During the preparation of the research project the main study area was selected on the basis of previous preliminary reseach results and concentrated on the western part of the basin. During the research project successive cooperation with foreign research groups resulted a very fruitfull cooperation with an aim to compare phreatomagmatic processes in the main study areas in the Pannonian Basin with other similar volcanic fields such as the Patagonian volcanic fields in Argentina, Transmexican volcanic belt in Mexico, Dolomites in Italy and many volcanic fields on SW Pacific islands. During the research period large amount of data collection took place from the western Hungarian study areas which hampered the extension of the project to the northern side of the basin. In this reason the reasearch project focused predominantly to the western side of the basin, and only preliminary results were obtained from the northern study areas

FINITE ELEMENT CALCULATION OF DOUBLE-CAGE SKIN FACTORS

Resistance and inductance skin factors for a double-cage induction motor are calculated as the ratio of AC and DC values in the 0-70Hz rotor frequency range by the help of a finite element analysis software. In this way, the parameters of a complete or correct equivalent circuit are determined which allows for the skin-effect in the outer and inner bars themselves. Results of calculation from the correct and the generally used approximate equivalent circuit are compared. If finite element analysis is available, the use of the correct equivalent circuit is proposed

Les pièges de la reconstitution des topographies d’érosion initiales fondée sur les vestiges des maars et diatrèmes volcaniques

Erosion estimates based on geometrical dimension measurements of eroded maar/diatreme volcanoes are useful methods to determine syn-volcanic surface level and syn-volcanic bedrock stratigraphy. However, such considerations on volcanic architecture should only be employed as a first-order approach to determine the state of erosion. We demonstrate, on both young and eroded maar/diatreme volcanoes, that establishing the volcanic facies architecture gives vital information on the environment in which the volcano erupted. In ‘soft’ rocks, maar volcanoes are broad and underlain by ‘champagne glass’-shaped diatremes. In contrast, the crater wall of maar volcanoes that erupted through ‘hard rocks’ will be steep, filled with lacustrine volcaniclastic deposits and underlain by deep diatremes

Geometry Optimization of Crystals by the Quasi-Independent Curvilinear Coordinate Approximation

The quasi-independent curvilinear coordinate approximation (QUICCA) method [K. N\'emeth and M. Challacombe, J. Chem. Phys. {\bf 121}, 2877, (2004)] is extended to the optimization of crystal structures. We demonstrate that QUICCA is valid under periodic boundary conditions, enabling simultaneous relaxation of the lattice and atomic coordinates, as illustrated by tight optimization of polyethylene, hexagonal boron-nitride, a (10,0) carbon-nanotube, hexagonal ice, quartz and sulfur at the $\Gamma$-point RPBE/STO-3G level of theory.Comment: Submitted to Journal of Chemical Physics on 7/7/0