The influence of mechanical stiffness on caldera deformation and implications for the 1971-1984 Rabaul uplift (Papua New Guinea)

Numerical models provide a link between measured ground deformation and the inaccessible deformation source, and here we present a systematic set of new results from numerical forward modelling using a Finite Element Method with application to volcano geodesy. We first provide a generic case analysis and then evaluate ground deformation data from the Rabaul caldera in Papua New Guinea. The generic case simulates surface displacements in a flat-topped caldera setting due to pressure changes in a shallow (at 5 km depth) oblate reservoir overlain by host rock with variable mechanical stiffness. Our main findings are: i) the amplitude and wavelength of resultant ground deformation are dependent on the distribution of mechanically stiff and soft lithologies and their relative distribution above the reservoir, ii) for a given pressure change, surface displacement may be amplified by the presence of soft layers compared to generic simulations using a homogeneous background medium, and iii) the ratio of maximum horizontal over maximum vertical deformation (uxxmax/uyymax) is particularly sensitive to the presence of rock heterogeneities. In assessing the influence of mechanical heterogeneities (as derived from seismic data) in caldera-fill successions on ground deformation at Rabaul we apply our model to inform on the source causing uplift between 1971 and 1984. The best-fit model involves a combination of two oblate sources at 3 and 1 km depth, respectively, beneath the centre of the caldera undergoing a reasonable pressure increment (∼ 38 MPa), compared to unrealistic pressurisation if modelled using a homogeneous background medium.The research was support by Spanish MEC (grant 2007–0400), the Royal Society and NERC.Peer Reviewe

Effects of damage-zone thickness on fault displacement

When viewed as ideal elastic cracks, seismogenic faults are often modeled as decreases from the host rock to the boundary between the core and the damage zone. mode II or mode III cracks in semiinfinite elastic bodies or half spaces. These models normally assume the rock to be homogeneous and isotropic. Such assumptions may be justified and necessary when using closed-form analytical solutions for fault displacement. They are not justified, however, when we attempt to understand fault-displacement profiles along earthquake rupture sites or in paleofault studies. This follows because crustal segments hosting faults are, as a rule, not homogeneous and isotropic, but rather heterogeneous and anisotropic. In particular, the fault rocks commonly form layers or units parallel with the fault plane. Also, the mechanical properties of the rocks next to the fault change as the fault develops (Gudmundsson 2004). During repeated earthquakes in a seismogenic fault zone, two main rock units develop around the fault plane. One unit is the core, located next to the fault plane and normally composed of soft (low Young’s modulus) breccia, gouge, and other cataclastic rocks. The other unit is the damage zone, containing some cataclastic rocks but characterized by fractures of various types...conferenc

A short review of our current understanding of the development of ring faults during collapse caldera formation

The term collapse caldera refers to those volcanic depressions resulting from the sinking of the chamber roof due to the rapid withdrawal of magma during the course of an eruption. During the last three decades, collapse caldera dynamics has been the focus of attention of numerous, theoretical, numerical, and experimental studies. Nonetheless, even if there is a tendency to go for a general and comprehensive caldera dynamics model, some key aspects remain unclear, controversial or completely unsolved. This is the case of ring fault nucleation points and propagation and dip direction. Since direct information on calderas' deeper structure comes mainly from partially eroded calderas or few witnessed collapses, ring faults layout at depth remains still uncertain. This has generated a strong debate over the detailed internal fault and fracture configuration of a caldera collapse and, in more detail, how ring faults initiate and propagate. We offer here a very short description of the main results obtained by those analog and theoretical/mathematical models applied to the study of collapse caldera formation. We place special attention on those observations related to the nucleation and propagation of the collapse-controlling ring faults. This summary is relevant to understand the current state-of-the-art of this topic and it should be taken under consideration in future works dealing with collapse caldera dynamics.Adelina Geyer is grateful for her Juan de la Cierva post-doctoral grant (JCI-2010-06092) and her Ramón y Cajal contract (RYC-2012-11024).Peer Reviewe

What Do We Know About Calderas?

The International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) Commission on Collapse Calderas organized its fourth workshop in the Vulsini Calderas District, Italy (http://www.gvb‐csic.es/CCC.htm). Vulsini includes the Bolsena and Latera calderas, formed in the past 0.6 million years. It is a famous type locality where fundamental concepts concerning caldera collapse and eruptive dynamics have been proposed

Stress controls of monogenetic volcanism: A review

The factors controlling the preparation of volcanic eruptions in monogenetic fields are still poorly understood. The fact that in monogenetic volcanism each eruption has a different vent suggests that volcanic susceptibility has a high degree of randomness, so that accurate forecasting is subjected to a very high uncertainty. Recent studies on monogenetic volcanism reveal how sensitive magma migration is to the existence of changes in the stress field caused by regional and/or local tectonics or rheological contrasts (stratigraphic discontinuities). These stress variations may induce changes in the pattern of further movements of magma, thus conditioning the location of future eruptions. This implies that a precise knowledge of the stress configuration and distribution of rheological and structural discontinuities at crustal level of such volcanic systems would aid in forecasting monogenetic volcanism. This contribution reviews several basic concepts relative to the stress controls of magma transport into the brittle lithosphere, and uses this information to explain how magma migrates inside monogenetic volcanic systems and how it prepares to trigger a new eruption. © 2016 Martí, López, Bartolini, Becerril and Geyer.This research was funded by the European Commission (FP7 Theme: NV.2011.1.3.3-1; Grant 282759: VUELCO and EC ECHO Grant SI2.695524: VeTOOLS). AG thanks the support provided by the Ramón y Cajal research program (RYC-2012-11024). We thank Gregg Valentine and Alessandro Tibaldi for their useful and constructive reviews.Peer reviewe

Koulutusasteen ja sukulaisella todetun rintasyövän yhteys vaihdevuosien hormonikorvaushoidon käyttöön ja koettuun rintasyöpäriskiin

Rintasyöpä on naisten yleisin syöpä sekä maailmalla että Suomessa. Riski sairastua rintasyöpään jossakin elämänvaiheessa on jokaisella naisella noin 10 %:n luokkaa, perinnöllisen alttiuden kattaessa noin 5-10 % kaikista sairastuneista. Vaihdevuosien hormonikorvaushoidon on osoitettu lisäävän rintasyöpäriskiä ja riskitietoisuuden on todettu vaihtelevan koulutustason mukaan. Myös sukulaisella todetun rintasyövän on tutkitusti todettu vaikuttavan oman syöpäriskin arviointiin ja ohjaavan naisten terveyskäyttäytymistä. Tutkimukseni aineisto kuuluu Syöpäjärjestöjen kyselytutkimukseen Elintavat, elämänlaatu ja terveys. Se on psykososiaalinen kyselytutkimus mammografiaseulonnan elintapa- ja elämänlaatuvaikutuksista. Kyselytutkimus aloitettiin keväällä 2012 yhteistyössä Suomen Syöpärekisterin, UKK-instituutin, Terveyden ja hyvinvoinnin laitoksen sekä Tampereen yliopiston kanssa. Tutkielma perustuu ensimmäisen kierroksen kyselyihin, joita lähetettiin 5000:lle vuonna 2012 49 vuotta täyttävälle naiselle. Lomakkeita palautui yhteensä 2615. Hormonaalisia tekijöitä koskevien kysymysten pohjalta tehtiin tilastollinen analyysi käyttäen menetelmänä ristiintaulukointia ja riippuvuustarkastelussa khiin neliötestiä. Tutkielmassa selvitettiin koulutusasteen ja sukulaisella todetun rintasyövän yhteyttä vaihdevuosien hormonikorvaushoidon käyttöön ja koettuun rintasyöpäriskiin. Tuloksina saatiin, että 49-vuotiaiden naisten hormonikorvausvalmisteiden käyttö on vielä vähäistä, eikä sillä ole tilastollista yhteyttä koulutusasteeseen tai sukulaisella todettuun rintasyöpään. Rintasyöpäriskiä ei koeta yleisesti suureksi, mutta suvussa todettu rintasyöpä ja koulutusaste ovat yhteydessä rintasyöpähuolestuneisuuteen

Designing of a volcano simulator

Peer Reviewe

Studying monogenetic volcanoes with a Terrestrial Laser Scanner: Case study at Croscat volcano (Garrotxa Volcanic Field, Spain)

Erosional processes (natural or anthropogenic) may partly destroy the relatively small-sized volcanic edifices characteristic of monogenetic volcanic zones, leaving their internal structure well exposed. Nevertheless, the study of these outcrops may be extremely challenging due to restricted accessibility or safety issues. Digital representations of the outcrop surface have been lately used to overcome such difficulties. Data acquired with terrestrial laser scanning instruments using Light Detection and Ranging technology enables the construction of such digital outcrops. The obtained high-precision 3-D terrain models are of greater coverage and accuracy than conventional methods and, when taken at different times, allow description of geological processes in time and space. Despite its intrinsic advantages and the proven satisfactory results, this technique has been little applied in volcanology-related studies. Here, we want to introduce it to the volcanological community together with a new and user-friendly digital outcrop analysis methodology for inexperienced users. This tool may be useful, not only for volcano monitoring purposes, but also to describe the internal structure of exposed volcanic edifices or to estimate outcrop erosion rates that may be helpful in terms of hazard assessment or preservation of volcanic landscapes. We apply it to the Croscat volcano, a monogenetic cone in the La Garrotxa Volcanic Field (Catalan Volcanic Zone, NE Spain), quarrying of which leads to a perfect view of its interior but restricts access to its uppermost parts. Croscat is additionally one of the most emblematic symbols of the La Garrotxa Volcanic Field Natural Park, and its preservation is a main target of the park administration

Characterization of the Outer Coast Tuff Formation - A way to unravelling the magmatic processes preceding and triggering Deception Island's caldera-forming eruption (Antarctica)

Deception Island (South Shetland Islands), discovered in 1820, is one of the most active volcanoes in Antarctica with more than 20 eruptions (including the historic eruptions of 1967, 1969 and 1970) and three documented volcanic unrest events (1992, 1999 and 2014-15) over the past two centuries. Deception Island currently hosts two scientific bases, which operate every year during the Austral summer, and is also one of the most popular tourist destinations in Antarctica. The island is a composite volcano with a centrally located caldera of 8.5 x 10 km dated at 3,980 ± 125 yr. BP. During the caldera-forming event, between 30 and 60 km3 (Dense Rock Equivalent-DRE) of magma, erupted in the form of dense basaltic-andesitic pyroclastic density current deposits. During the last decades, Deception Island has been intensively investigated but some aspects regarding the magmatic processes associated with the formation of its caldera collapse are still under research and debate. For instance, characterizing the magmatic conditions and processes that triggered the huge explosive event is crucial to understand the past (and in turn the future) magmatic and volcanic evolution of the island

Designing of a vulcano simulator

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