Search results for "Geophysics"

2015

Large volcanic eruptions are major geohazards, so identifying their frequency in the geologic record is critical for making predictions and hazard assessments. Following the discovery of a thick (18 cm) tephra layer in marine sediments from Integrated Ocean Drilling Program (IODP) Site U1396 between Montserrat and Guadeloupe in the Caribbean Sea, we document here how high-precision Pb isotopes, trace elements, and grain morphological analyses of the tephra can be used, together with volcanological models, to identify a large (Volcanic Explosivity Index ?6) Plinian eruption from Basse-Terre, Guadeloupe, at ca. 2.36 Ma. This previously unrecognized eruption is believed to be the largest docum…

NO EXCESSIVE CRUSTAL GROWTH IN THE CENTRAL ASIAN OROGENIC BELT: FURTHER EVIDENCE FROM FIELD RELATIONSHIPS AND ISOTOPIC DATA

2017

Abstract We provide new field observations and isotopic data for key areas of the Central Asian Orogenic Belt (CAOB), reiterating our previous assessment that no excessive crustal growth occurred during its ca. 800 Ma long orogenic evolution. Many Precambrian blocks (microcontinents) identified in the belt are exotic and are most likely derived from the northern margin of Gondwana, including the Tarim craton. Ocean opening in the Palaeo-Asian Ocean, arc formation and accretionary processes began in the latest Mesoproterozoic along the southern margin of the Siberian craton and continued into the Neoproterozoic, giving rise to tectono-metamorphic terranes distinct from the exotic microcontin…

Turmoil at Turrialba Volcano (Costa Rica): Degassing and eruptive processes inferred from high-frequency gas monitoring

2016

Eruptive activity at Turrialba Volcano (Costa Rica) has escalated significantly since 2014, causing airport and school closures in the capital city of San Jose. Whether or not new magma is involved in the current unrest seems probable but remains a matter of debate as ash deposits are dominated by hydrothermal material. Here we use high-frequency gas monitoring to track the behavior of the volcano between 2014 and 2015 and to decipher magmatic versus hydrothermal contributions to the eruptions. Pulses of deeply derived CO2-rich gas (CO2/S-total>4.5) precede explosive activity, providing a clear precursor to eruptive periods that occurs up to 2weeks before eruptions, which are accompanied by…

Geoarchaeological investigations of a prominent quay wall in ancient Corcyra: Implications for harbour development, palaeoenvironmental changes and t…

2018

Abstract In antiquity, the harbour-city of Corcyra (modern: Corfu) was a prevailing naval power in the Mediterranean and had several harbours to host a considerable fleet. Today, these harbours are totally or partly silted and concealed under modern urban infrastructure. Comprehensive geoarchaeological studies were conducted on the northeastern fringe of the Analipsis Peninsula where excavations have revealed the archaeological remains of a massive quay wall (Pierri and Arion sites). These remains are located east of known ancient harbour structures that belong to the Alkinoos Harbour. Our study aimed to reconstruct the palaeoenvironmental setting of the harbour facilities at the Pierri sit…

H2O-content and temperature limit the explosive potential of rhyolite magma during Plinian eruptions

2019

Abstract Recent rhyolite eruptions on Earth have demonstrated their capacity to produce a multitude of hazards, including ash formation lasting months and impacting the large reaches of the southern hemisphere. Nevertheless, the underlying mechanisms driving these eruptions are not yet fully understood. Magmatic volatiles, especially H2O, dictate whether volcanic eruptions proceed explosively or effusively. Experimental evidence for the role played by H2O in driving explosive fragmentation is rare, in particular in the eruption of rhyolitic magma. Here we show that when hydrous rhyolitic obsidians from Chaiten Volcano (Chile) are experimentally heated above their glass transition temperatur…

Ultraviolet camera measurements of passive and explosive (Strombolian) sulphur dioxide emissions at Yasur volcano, Vanuatu

2020

Here, we present the first ultraviolet (UV) camera measurements of sulphur dioxide (SO2) flux from Yasur volcano, Vanuatu, for the period 6–9 July 2018. These data yield the first direct gas-measurement-derived calculations of explosion gas masses at Yasur. Yasur typically exhibits persistent passive gas release interspersed with frequent Strombolian explosions. We used compact forms of the “PiCam” Raspberry Pi UV camera system [1,2] powered through solar panels to collect images. Our daily median SO2 fluxes ranged from 4 to 5.1 kg s−1, with a measurement uncertainty of −12.2% to +14.7%, including errors from the gas cell calibration drift, uncertainties in plume direction and distance, and…

Mapping fumarolic fields in volcanic areas: A methodological approach based on the case study of La Fossa cone, Vulcano island (Italy)

2016

Abstract Changes in the activity state of a volcano can be inferred by monitoring the steam flux from fumarolic fields, in terms of 4D (x, y, z, time) variations in temperature and extension of the zone. During the last decades, several studies in this field have been conducted worldwide, and at Vulcano island (Italy) in particular. Both direct and remotely sensed measurements have been used for identifying thermally anomalous areas, but the possible role of the hydrothermal alteration of volcanic products, producing a sealing effect that obscures the surface thermal evidence of fumarolic activity, have never been explored. The novelty of the present study, carried out at La Fossa cone (Vul…

First observations of the fumarolic gas output from a restless caldera: Implications for the current period of unrest (2005-2013) at Campi Flegrei

2013

[1] The fumarolic gas output has not been quantified for any of the currently deforming calderas worldwide, due to the lack of suitable gas flux sensing techniques. In view of resumption of ground uplift (since 2005) and the associated variations in gas chemistry, Campi Flegrei, in southern Italy, is one of the restless calderas where gas flux observations are especially necessary. Here we report the first ever obtained estimate of the Campi Flegrei fumarolic gas output, based on a set of MultiGAS surveys (performed in 2012 and 2013) with an ad-hoc-designed measurement setup. We estimate that the current Campi Flegrei fumarolic sulphur (S) flux is low, on the order of 1.5–2.2 tons/day, sugg…

Geochemistry and SHRIMP U-Pb Zircon Dating of Mafic Rocks North of Zunhua City, Eastern Hebei, North China Craton: Paleoproterozoic Gabbro rather tha…

2018

Late Holocene erosion of the Canopic promontory (Nile Delta, Egypt)

2017

International audience; The mouths of the Nile Delta are sensitive coastal areas, their geomorphology primarily being mediated by relative sea-level rise and sediment supply. To further document the Holocene evolution of the Nile's Canopic mouth, a core was taken from the southern shores of Abu Qir Bay, close to the ancient Canopic channel. Core bio-sedimentology and chronostratigraphy highlight four stages of marine incursion which are juxtaposed upon the general progradation trend of the Nile coast in this area. Compiled age-depth points from sediment cores taken in Abu Qir Bay underscore two phases of negative sediment budget at the Canopic mouth: (1) a first period, between 3.5 and 2 ka…