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Jaime L. B. Presser, Ricardo Alonso & Maximiliano Rocca

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Presser, J.L.B., Alonso, R., Rocca, M. 2019. Malvinas Islands (Falkland Islands): Advances in the inferred buried marine impact mega-structure. Pyroclastic Flow Journal of Geology, Vol. 9, no. 1, p. 1-14.



In 1992 Rampino noticed a large, almost circular negative gravity anomaly (~30 mGal) on the Falkland Plateau to the WNW of Malvinas Islands/Falkland Islands using satellite data then available, and speculated that it might be associated with a large (~250 km wide?) buried impact structure. In some more recent compilations Rocca & Presser (2015) and Rocca et al. (2017) was attended the Malvinas Islands/Falkland Islands “buried impact structure” with particular care; but also these works was harshly criticized. The present text, which is an advance to demonstrate the certain possibilities that this Malvinas Islands/Falklnad Islands It could really be a very probable mega impact structure, gathers shows and evaluates the existing and available indirect information; like gravimetry (Isostasy, Free-air and Bouguer); seismic reflection (Geco Prakla); and, even commenting aspects of its magnetic behavior and its local geology. In all gravimetric analyses from the Malvinas Islands/Falklnad Islands “buried impact structure” it can be shown that an annulus of positive gravity anomaly surrounding a circular oval depression of negative (isostasy and Free-air)/much lower (Bouguer) values gravity anomaly. The most relevant gravimetric information would be the near circular to oval Bouguer gravity low anomaly (with a minimum value of ~150 mGal) surrounded by at least circular ~255 kilometers wide circular ring of positive gravity anomaly (maximum ~225 mGal); a very high values of Bouguer anomaly that are highly compatible with what is expected to be found in mega impact structures. The Malvinas probable impact structure shows almost 100 mGal superior to the volcanic complex of Iceland; so it seems obvious that Malvinas probable impact structure moves away from a speculation by mega-paleo-volcano origin. When gravimetrically modeled, a probable peak ring of ~255 km is evidenced; as well as, the inferred the ~550 km probable rim-crest; configuration that reproduces an almost perfect and symmetrical modeling of a very probable giant impact structure with its clear visible the very probable elements: rim crest-annulus basin-peak ring-central basin-peak ring-annulus basin-rim crest. Four Geco Prakla seismic reflection lines on the area located to the SW of the potential peak ring show a vertical and disturbed crystalline basement (the “peak ring”); in three of them, the “central basin” what would it be filled with sediments after impact (probable ejecta). Using the empirical formula of Assumpção et al. (2013) calculation for crustal thickness could be found very clearly strong CT distortion along Malvinas very probable giant impact structure: around 3400-4000 meters; as is to be expected in terrestrial mega impact structure. Harness the EMAG2v3 a global Earth Magnetic Anomaly Grid compiled from satellite (Meyer et al.,  2017) for the Malvinas very probable giant impact structure a well superior anomaly was found and better definition than observed, using the same information, to the one characterized by the impact crater Chicxulub. The geological map of the Falkland Islands Government that was placed ontop of the modeling isostasy gravimetric map where the approximate circumference of the very probable peak-ring and the very probable rim-crest is highlighted. This information allows to see that the largest island (West Malvinas) would be part of the very probable peak-ring and the smaller island (East Malvinas) would be part of the very probable rim-crest; both separated by the depression that would correspond to the very probable annulus basin. Based on what was analyzed in the Malvinas Islands area, we concluded the Malvinas exhibited geophysics traits of a large ancient asteroid impact; i.e. Malvinas very probable giant impact structure. Very probable impact structure what could be among one of the world's largest impact crater.


Islas-Malvinas/Falkland-Islands, impact-basin, gravimetric-modeling, seismic-data

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Autor: Jorge E. Romero

Cita APA: Romero, J. E. (2011). TERREMOTOS, TSUNAMIS Y ERUPCIONES VOLCÁNICAS: Los principales peligros geológicos de Chile. Pyroclastic Flow. Journal of Geology, 1(2)

RESUMEN:  Este material se presenta como una nueva herramienta para la educación de la ciudadanía común en la comprensión de los fenómenos naturales que se desarrollan en nuestro país, en este caso los de origen geológico. Desde ya, cabe aclarar que la publicación ha sido producida sin fines de lucro, por lo que su disponibilidad y acceso son completamente libres y gratuitos para quienes deseen consultarla .

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Autor: Jorge E. Romero

Cita APA: Romero, J.E., 2011. The evolution of the 2008-2011 eruptive cycle at Chaiten volcano, 42º83’ S, Southern Chile. Pyroclastic Flow, Journal of Geology, Vol. 1, nº 1, 10 pp.

ABSTRACT: Chaitén volcano is a small caldera located close to the Chaitén town, in the South of Chile. It was ignored by the population and authorities because there was not historical register about activity before 2008 eruption. The most recent 2008-2011 eruptive cycle of the small Chaitén caldera, was one of the most explosive eruptions in the history of chilean volcanic eruptions. The volcano emited medium quantities of ashes to the atmosphere (around 1-2 cubic kilometers aparently) and ashs were not much dangerous. This eruptive cycle was followed by a rhyolitic lava dome growing in the summit area of the old dome, that involved structural collapses, lateral explosions and lahars. Now, eruption is decreasing steadily and the activity is very reduced, but volcanic hazards are latent, mainly debris flows, lahars and directed explosions. At this time this eruption can be considered one of the bigger with Eyjafjallajokulln in this century, smaller than(in relation with the emitted material) Hudson 1991 or Saint Helens 1980 eruptions.

Keywords: Eruprive cycle, plinian eruption, lava dome, lahar, pyroclastic flow, collapse, caldera.

RESUMEN: El volcán Chaitén es una pequeña caldera ubicada en las cercanías del pueblo de Chaitén, en el Sur de Chile. Este estuvo ignorado, tanto por la población como por las autoridades debido a que no existía registro histórico de su actividad antes de su erupción en 2008. El ciclo eruptivo más reciente de 2008-2011 de la pequeña caldera del Chaitén fue uno de los más explosivos en la historia de las erupciones volcánicas en Chile. El volcán emitió medianas cantidades de cenizas a la atmósfera (entre 1-2km3 aparentemente) y estas no fueron tan dañinas. Este ciclo eruptivo estuvo seguido del crecimiento de un domo de lava riolítica en la cima del domo de lava antiguo, que incorporó colapsos estructurales, explosiones laterales y lahares. Ahora, la erupción está en disminución sostenida y la actividad es muy reducida, pero los peligros volcánicos continúan latentes, principalmente los flujos de detritos, lahares y explosiones dirigidas. En este momento se puede considerar a esta erupción como una de las mayores del siglo junto con la del Eyjafjallajokulln, menor (en relación a la cantidad de material emitido) que las erupciones del Hudson en 1991 o Monte Santa Helena en 1980.

Palabras clave: Ciclo eruptivo, erupción pliniana, domo de lava, lahar, flujo piroclástico, colapso, caldera.

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