Stratigraphy and age of the Cappadocia ignimbrites, Turkey: reconciling field constraints with paleontologic, radiochronologic, geochemical and paleomagnetic data

The stratigraphy and age of the Neogene Cappadocia ignimbrites (Central Turkey) have been inferred in previous studies from fieldwork and K–Ar age determinations. The resulting stratigraphic schemes, however, differed from each other, suggesting that further studies were required to produce a reliable succession. In this paper, we examine the chronostratigraphy of mammalian remains recovered in the continental sediments interbedded with the Cappadocia ignimbrites. Using recent advances in mammalian chronostratigraphy, we evaluate selected taxa and faunal associations to place new and independent constraints on the ignimbrite ages. The biostratigraphically bracketed ages concur with some published radiometric dates, but they disagree with others, principally at localities where major stratigraphic discrepancies have arisen in the literature. In order to reconcile these apparent inconsistencies, we combine, at selected sites, our field observations with the biostratigraphic and radiometric age limits, and we compare these with the available geochemical and magnetic data. This allows us to present revised age estimates, and a revised stratigraphy which includes the correlation of the local Sofular deposits with the large-volume Gördeles ignimbrite. The issues faced in this study apply to other ignimbrite provinces in the world. For instance, ignimbrite eruption frequency in Cappadocia is higher than the resolution of many published K–Ar ages. Furthermore, different K–Ar ages have led to the description of individual and distinct ignimbrites that fieldwork and geochemical data allow to merge into a single ignimbrite. Argon loss from pumice samples leading to radiometric “rejuvenation” provides a likely explanation for most stratigraphic discrepancies. Cappadocia is the only documented ignimbrite field in which the chronostratigraphy of vertebrate remains provides better constraints on some ignimbrite ages than scattered K–Ar dates. We further argue that K–Ar dates from the Cappadocia area are too imprecise to establish a reliable magnetostratigraphic scheme for the ignimbrite succession, with the exception of the not, vert, similar2.8 Ma Valibaba Tepe ignimbrite

Ejemplos de deformación producto de la tectónica extensiva en las zonas de Huambo-Cabanaconde en Arequipa y Calacoa-Huaytire en Moquegua, de los Andes Centrales vistos por Interferometría Radar – Insar

En este trabajo se presentan los primeros resultados obtenidos por el método InSAR para la detección y medida del campo de deformación co-sísmico asociado a eventos sísmicos ocurridos en el sur del Perú. Interferogramas calculados sobre la zona de los poblados Huambo-Cabanconde (departamento de Arequipa) y sobre la zona de Calacoa (departamento de Moquegua), han permitido registrar procesos de deformación del suelo asociados a la tectónica extensiva superfi cial, la que viene actuando en los Andes Centrales desde el Mioceno medio. El primer ejemplo de deformación ha sido detectado en la zona Huambo-Cabanaconde. El interferograma calculado con imágenes adquiridas el 06/12/2002 y 12/09/2003, muestra una subsidencia en la Pampa Mojonpampa, hacia el sur de la falla normal Solarpampa, que forma parte del sistema de fallas Huambo-Cabanaconde. Esta subsidencia habría sido producida por sismos de magnitud Mb > 4 ocurridos entre el 13/12/2002 y 14/12/2002, los mismos que se producen por esfuerzos extensivos que actúan en dirección N-S. Un segundo ejemplo de deformación ha sido detectado en dos interferogramas de la zona de Calacoa (departamento de Moquegua), calculados con imágenes adquiridas entre el 01/12/2004 y el 13/05/2006. Esta deformación está muy probablemente relacionada a un sismo de magnitud Mw 5.4 que corresponde al evento principal de la crisis sísmica ocurrida en octubre del 2005 en la región del volcán Ticsani. Esta crisis sísmica consiste en una sismicidad superfi cial intracrustal asociada a la actividad de una falla local N155º. El área de deformación producida fue de 15 x 12 km aproximadamente, y registró una amplitud máxima de 14 cm a 3.5 km al NO de la cima del volcán Ticsani. Las características de la falla N155º han sido puestas en evidencia por los datos interferométricos. Un tercer ejemplo de deformación ha sido observado a 25 km al SE del volcán Ticsani, en un área elíptica de aproximadamente 24.5 x 11.7 km orientada en dirección NO-SE y cuya amplitud máxima de deformación fue de 5.5 cm (subsidencia). Esta deformación se habría producido entre diciembre de 2004 y mayo de 2006 y puede ser atribuida a la ocurrencia de una crisis sísmica durante este periodo

Sheared sheet intrusions as mechanism for lateral flank displacement on basaltic volcanoes: Applications to Réunion Island volcanoes

International audienceField work carried out on the Piton des Neiges volcano (Réunion Island) suggests that the injection of magma along detachments could trigger flank failure by conjugate opening and shear displacement. We use 3-D numerical models to compare the ability of purely opened sheet intrusions, sheared sheet intrusions, and normal faults to induce flank displacement on basaltic volcanoes. We assume that shear stress change on fractures results from stress anisotropy of the host rock under gravity. Exploring a large range of stress anisotropies, fracture dips, and fracture depth over length ratios, we determine that the amount of shear displacement is independent of the proximity to the ground surface. Sheared sheet intrusions are the most efficient slip medium on volcanoes. Consequently, the largest flank displacement is induced by the longest, deepest sheared intrusion dipping closest to 45° in a host rock with the highest stress anisotropy. Using our model in a forward way, we provide shear and normal displacements for buried fractures. Applying the model to a pile of sills at the Piton des Neiges volcano, we determine that the mean shear displacement caused by each intrusion was 3.7 m, leading to a total of a 180–260 m of lateral displacement for the 50 m high pile of sills. Using our model in an inverse way, we formulate a decision tree to determine some fracture characteristics and the host rock stress anisotropy from ratios of maximum surface displacements. This procedure provides a priori models, which can be used to bound the parameter space before it is explored through a formal inversion. Applying the decision tree to the 1.4 m coeruptive flank displacement recorded at Piton de la Fournaise in 2007, we find that it probably originated from a shallow eastward dipping subhorizontal normal fault

Deformación co-sísmica producida por el sismo MB=5.4 del 01 de octubre de 2005 (Carumas-Moquegua), detectada por interferometría radar-INSAR

Trabajo realizado en Carunas, Moquegua, sobre la deformación co-sísmica producida por el sismo MB=5.4 del 01 de octubre de 2005. Se presentan los primeros resultados obtenidos por el método InSAR, para la medida del campo de deformación co-sísmico, producido por eventos correspondientes a una sismicidad superficial intracrustal como lo es el caso del sismo de Carumas. Se aplica la técnica geodésica de Interferometría Radas InSAR (SAR-Radar de Apertura Sistémica) para el estudio de la deformación producida antes, durante y después de los sismos. Se basa en la utilización de datos satelitales radar. El trabajo ha sido elaborado en conjunto por INGEMMET, la Comisión Nacional de Investigación y Desarrollo Aeroespacial, CONIDA y el Instituto de Investigación para el desarrollo, IRD

INTERFÉROMÉTRIE RADAR APPLIQUÉE AUX VOLCANS : CAS DE L’ETNA ET DES CHAMPS PHLÉGRÉENS (ITALIE)

During the last few years, the radar images collected by the European satellites ERS1 and ERS2, the Japanese satellite JERS and the Canadian satellite RADARSAT have been used with success to create interferograms. This technique has been applied for geophysical applications like co-seismic deformation mapping, volcano deformation monitoring, landslides monitoring, mining subsidence detection, glaciers monitoring. Here we report the research carried out by our group on Etna volcano (Italy) and in the area of Naples (Italy) where are located several potentially active volcanoes (Vesuvius, Ischia) and where a subsidence of the caldera of Campi Flegrei is still on going in response to the 1982-1984 seismic crisis. Etna is the volcano that has been studied first using ERS SAR interferometry. Using this method, a large scale deflation of the volcano associated with the large 1991-1993 eruption was detected in data covering the second half of the eruption. Further studies showed that the local deformation fields located in Valle del Bove (East of the volcano) where associated with the compaction of the 1986-1987 and 1989 lava fields and also partly with a subsidence of the surrounding terrain in response to the load of the new deposited material. Other local deformation fields have been identified, corresponding to the 1983, 1981 and 1971 lava fields. However, due to its strong topography, interferograms of Etna are affected by tropospheric effects. Those effects must be eliminated in order to correctly interpret the fringes pattern. The problem of the troposphere has been first investigated from its theoretical point of view and using existing local meteorological data as well as radio-soundings data. Recently, thanks to the large amount of available interferograms, another approach has been investigated, consisting in the research of a correlation fringe/elevation in the interferograms themselves. This approach, operated either in automatic mode (automatic fringe unwrapping) or in manual mode proved to be efficient for most of the coherent interferograms. After removal of the tropospheric correction, the evolution of the deformation of the volcano at large scale between 1992 and 1998 has been inferred. The subsidence occurring during the second half of the 1992 eruption as well as the uplift preceding the 1995 unrest of the Southeast crater are visible, but their amplitude is less than previously estimated. The depth of the modelled source of subsidence/uplift related to the large scale deformation is of the order of 6 to 8 km, not well constrained by the data. The study of the correlation fringe/elevation was possible only after a detailed analysis of the spatial and temporal properties of coherence of the Etna area. Indeed, the technique of fringe unwrapping for fringe/elevation correlation analysis is possible only if the poorly coherent pixels are eliminated. A map of the most coherent pixels of the volcano was produced. The recent lava fields as well as the towns and villages surrounding the volcano are the most coherent areas. The quality of the interferograms is also enhanced when high accuracy DEM (Digital Elevation Model) are used. Using kinematic GPS data collected along more than 100 km of road around the volcano, we assessed the accuracy of several DEMs of Etna. The most accurate DEM was produced by digitising 1/25.000e maps of Etna. This DEM does not take into account the topographic changes due to the recent eruptions. Merging other more recent DEMs corresponding to those areas, we produced an updated relatively high accuracy DEM (±3 m) of Etna. In the Naples area, we analysed interferograms in the period 1993-1996 and show that the Campi Flegrei caldera is still subsiding at a rate of about 30 mm/year

Implementación de redes geodésicas para monitoreo de los volcanes Misti y Ubinas

La geodesia es uno de los métodos más empleados para la detección anticipada de los cambios de estado de un volcán que pudiera evolucionar en una erupción. El objetivo principal de este método es la medición de las deformaciones del suelo en los edificios volcánicos aplicando diversas técnicas geodésicas. En este trabajo describimos la metodología, técnicas y los avances que el INGEMMET ha logrado en la implementación de redes geodésicas en los volcanes Misti y Ubinas. La región sur del Perú pertenece a la Zona Volcánica de los Andes Centrales (ZVC), donde se han identificado 7 volcanes activos, es decir que tienen grandes probabilidades de iniciar un nuevo proceso eruptivo en cualquier momento, Entre estos volcanes activos destacan el volcán Ubinas con una reciente erupción que se inició en el año 2006 y el volcán Misti, que se encuentra a solo 17 Km de la ciudad de Arequipa (~1 millón de habitantes). Esta ciudad así como todos los pueblos que se encuentran cerca de edificios volcánicos están bajo un riesgo latente de una probable erupción volcánica. La mitigación de este riesgo y su actualización continua puede lograrse con el monitoreo, esto implica la observación persistente de diversos parámetros principalmente sismológicos, geodésicos y geoquímicos, que en el caso de un cambio interno del estado del volcán pueden variar significativamente. Si estas variaciones pueden ser identificadas como precursoras de una erupción y se consigue poner en marcha un mecanismo de respuesta encaminado a la protección de la población se habrían alcanzado los objetivos de vigilancia volcánica y la efectiva reducción de riesgo a través de la disminución de la vulnerabilidad. Bajo estas consideraciones el INGEMMET está desarrollando un sistema de vigilancia de volcanes activos implementando técnicas geodésicas con la finalidad de monitorear las deformaciones del suelo como producto de los procesos volcánicos, se instalan hitos geodésicos y se miden su posición relativa o absoluta. Para este efecto, se emplean técnicas de geodesia clásica como son la medida electromagnética de distancias y ángulos (EDM), medidas con GPS Diferencial y el análisis continuo de imágenes satelitales (InSAR). Complementariamente se realizará la instalación de inclinómetros electrónicos permanentes con transmisión telemétrica

The role of Interferometric Synthetic Aperture Radar in Detecting, Mapping, Monitoring, and Modelling the Volcanic Activity of Piton de la Fournaise, La Réunion: A Review

Synthetic Aperture Radar (SAR) remote sensing plays a significant role in volcano monitoring despite the measurements’ non real-time nature. The technique’s capability of imaging the spatial extent of ground motion has especially helped to shed light on the location, shape, and dynamics of subsurface magmatic storage and transport as well as the overall state of activity of volcanoes worldwide. A variety of different deformation phenomena are observed at exceptionally active and frequently erupting volcanoes, like Piton de la Fournaise on La Réunion Island. Those offer a powerful means of investigating related geophysical source processes and offer new insights into an active volcano’s edifice architecture, stability, and eruptive behavior. Since 1998, Interferometric Synthetic Aperture Radar (InSAR) has been playing an increasingly important role in developing our present understanding of the Piton de la Fournaise volcanic system. We here collect the most significant scientific results, identify limitations, and summarize the lessons learned from exploring the rich Piton de la Fournaise SAR data archive over the past ~20 years. For instance, the technique has delivered first evidence of the previously long suspected mobility of the volcano’s unsupported eastern flank, and it is especially useful for detecting displacements related to eruptions that occur far away from the central cone, where Global Navigation Satellite System (GNSS) stations are sparse. However, superimposed deformation processes, dense vegetation along the volcano’s lower eastern flank, and turbulent atmospheric phase contributions make Piton de la Fournaise a challenging target for applying InSAR. Multitemporal InSAR approaches that have the potential to overcome some of these limitations suffer from frequent eruptions that cause the replacement of scatterers. With increasing data acquisition rates, multisensor complementarity, and advanced processing techniques that resourcefully handle large data repositories, InSAR is progressively evolving into a near-real-time, complementary, operational volcano monitoring tool. We therefore emphasize the importance of InSAR at highly active and well-monitored volcanoes such as Mount Etna, Italy, Kīlauea Volcano, Hawai’i, and Piton de la Fournaise, La Réunion

Is stress modeling able to forecast intrusions and slip events at Piton de la Fournaise volcano ?

Widespread evidence indicates that the stress field and the presence of major discontinuities control the magma trajectory and the stability of volcanic edifices. These latter factors affect two major volcanic hazards: eruptions and flank slip events. Here, we use a catalog of 60 intrusions at Piton de la Fournaise (R´eunion Island) to document the link between stress inherited from intrusions and slip events, and the location of subsequent events. Our study spans two periods, 1998-2007 and 2007-2021, separated by a collapse of the summit crater and a 1.4 meter flank slip in 2007. The 1998-2007 intrusive sequence cannot be explained by stress interaction. On the contrary, the location of intrusions in the 2007-2021 sequence is consistent with a decrease in normal stresses (unclamping) induced by previous intrusions. Progressive rift zone unclamping, and Coulomb stress increase on previously recognized structures explain the migration of activity from the summit to distal areas, the alternation between intrusions in the northern and the southern flanks, as well as the occurrence of flank slip events. Stress analysis documents a positive feedback between rift zone and flank slip events. In the long term, both magma intrusions and flank slip events contribute to the occurrence of catastrophic flank collapses through unclamping and Coulomb stress increase at the base of an unstable sector

Is stress modeling able to forecast intrusions and slip events at Piton de la Fournaise volcano ?

Widespread evidence indicates that the stress field and the presence of major discontinuities control the magma trajectory and the stability of volcanic edifices. These latter factors affect two major volcanic hazards: eruptions and flank slip events. Here, we use a catalog of 60 intrusions at Piton de la Fournaise (R´eunion Island) to document the link between stress inherited from intrusions and slip events, and the location of subsequent events. Our study spans two periods, 1998-2007 and 2007-2021, separated by a collapse of the summit crater and a 1.4 meter flank slip in 2007. The 1998-2007 intrusive sequence cannot be explained by stress interaction. On the contrary, the location of intrusions in the 2007-2021 sequence is consistent with a decrease in normal stresses (unclamping) induced by previous intrusions. Progressive rift zone unclamping, and Coulomb stress increase on previously recognized structures explain the migration of activity from the summit to distal areas, the alternation between intrusions in the northern and the southern flanks, as well as the occurrence of flank slip events. Stress analysis documents a positive feedback between rift zone and flank slip events. In the long term, both magma intrusions and flank slip events contribute to the occurrence of catastrophic flank collapses through unclamping and Coulomb stress increase at the base of an unstable sector

Multiscale Change Analysis for SAR Image Time Series: Application to Inundation Detection

International audiencehis paper presents a multiscale framework for change analysis using a big dataset of multitemporal Synthetic Aperture Radar (SAR) images. In patch scale, spatio-temporal change information can be extracted by the Patch-based Change Detection Matrix (P-CDM). Then regions and acquisitions of interest that show where and when changes occurred are determined from obtained P-CDMs. In pixel scale, for each such region, changes are detected in details between selected acquisitions using statistical similarity measure. This approach was then applied for analyzing changes along central coast of Vietnam (from Hue to Quang Ngai) by using a time series including 19 Sentinel-1 images. The experimental results have shown the relevancy of the framework in detecting abrupt and seasonal changes, and its effectiveness in processing a long time series with large size images