Search results for "phreatomagmatic eruption"
showing 10 items of 17 documents
Maars of the Westeifel, Germany
2008
Within the Westeifel Volcanic Field 27% of the 250 Quaternary eruptive centers are maars. Maars form as a result of a highly explosive interactive process between rising melt and groundwater. In the Westeifel, probably thermal water plays an important role for the productive phreatomagmatic interaction process and, con-sequently, the high number of maars. The Westeifel maars show all transitions to scoria cones. Only the youngest maars are filled by a maar lake or a raised bog, and are well preserved. The older maars show a low diameter to depth ratio. Nearly one third of the Westeifel maars were formed during the Weichselian glaciation period. The isostatic movements during the increasing …
Volcanic Lakes in Africa: The VOLADA_Africa 2.0 Database, and Implications for Volcanic Hazard
2021
Volcanic lakes pose specific hazards inherent to the presence of water: phreatic and phreatomagmatic eruptions, lahars, limnic gas bursts and dispersion of brines in the hydrological network. Here we introduce the updated, interactive and open-access database for African volcanic lakes, country by country. The previous database VOLADA (VOlcanic LAke DAta Base, Rouwet et al., Journal of Volcanology and Geothermal Research, 2014, 272, 78–97) reported 96 volcanic lakes for Africa. This number is now revised and established at 220, converting VOLADA_Africa 2.0 in the most comprehensive resource for African volcanic lakes: 81 in Uganda, 37 in Kenya, 33 in Cameroon, 28 in Madagascar, 19 in Ethiop…
Contrasting styles of deep-marine pyroclastic eruptions revealed from Axial Seamount push core records
2015
Abstract A comprehensive understanding of explosive basaltic eruption processes in the deep-sea relies upon detailed analysis and comparison of the variety of volcaniclastic lithologies on the seafloor, which has been challenged by insufficient sample recovery. A dedicated ROV-based sampling approach using long push cores offers an unparalleled opportunity to fully characterize the diversity of unconsolidated volcaniclastic lithofacies on a recently active seamount. Lithofacies from Axial Seamount record two styles of pyroclastic eruptions, strombolian and phreatomagmatic, at 1.5 km water depth. Strombolian eruptions are represented by abundant fluidal and highly vesicular (up to 50%) vitri…
Geothermal energy release at the Solfatara of Pozzuoli (Phlegraean Fields): Phreatic and phreatomagmatic explosion risk implications
1984
The H2O, CO2 and H2S outputs at the Solfatara of Pozzuoli have been measured and a map of the exhaling areas has also been made. The energy released at the surface by the fluids has been estimated to be 1019 ergs/day. The presence of aquifers at Phlegraean Fields increases the phreatic and phreatomagmatic explosion risk. Our results suggest that even if an uprising magma may interact with water at depth, an explosion could occur only at the shallow levels of a few hundred meters. Since the transfer of energy toward the surface is favoured by the presence of fractures, a detailed analysis of the deep fracture network would help to evaluate the risk levels of the various areas of Phlegraean F…
FORMATION OF PHREATOMAGMATIC MAAR–DIATREME VOLCANOES AND ITS RELEVANCE TO KIMBERLITE DIATREMES
1975
ABSTRACT Studies of maars and diatremes suggest a specific process in their formation. Magma rises along a fissure and contacts ground– or surface derived water. The resulting phreatomagmatic eruptions give rise to base surge and air–fall deposits consisting of juvenile and wall–rock material. Spalling of the wall–rocks enlarges the fissure into an embryonic vent. At a critical diameter of the vent large-scale spalling at depth and slumping near the surface gives rise to a ring–fault of large diameter and subsidence of the enclosed wall–rocks and overlying pyroclastic debris. This subsidence leads to a maar crater at the surface. Fluidization processes are active in the narrow vent and in f…
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…
The summit hydrothermal system of Stromboli: New insights from self-potential, temperature, CO2 and fumarolic fluids measurements, with structural an…
2003
International audience; Accurate and precisely located self-potential (SP), temperature (T) and COi measurements were carried out in the summit area of Stromboli along 72 straight profiles. SP data were acquired every metre and T data every 2.5 m. CO2 concentrations were acquired with the same density as T, but only along seven profiles. The high density of data and the diversity of the measured parameters allows us to study structures and phenomena at a scale rarely investigated. The shallow summit hydrothermal activity (Pizzo-Fossa area) is indicated by large positive SP, T and COi anomalies. These anomalies are focused on crater faults, suggesting that the fracture zones are more permeab…
The ELSA tephra stack: Volcanic activity in the Eifel during the last 500,000 years
2016
Abstract Tephra layers of individual volcanic eruptions are traced in several cores from Eifel maar lakes, drilled between 1998 and 2014 by the Eifel Laminated Sediment Archive (ELSA). All sediment cores are dated by 14C and tuned to the Greenland interstadial succession. Tephra layers were characterized by the petrographic composition of basement rock fragments, glass shards and characteristic volcanic minerals. 10 marker tephra, including the well-established Laacher See Tephra and Dumpelmaar Tephra can be identified in the cores spanning the last glacial cycle. Older cores down to the beginning of the Elsterian, show numerous tephra sourced from Strombolian and phreatomagmatic eruptions,…
Thematic vent opening probability maps and hazard assessment of small-scale pyroclastic density currents in the San Salvador volcanic complex (El Sal…
2021
The San Salvador volcanic complex (El Salvador) and Nejapa-Chiltepe volcanic complex (Nicaragua) have been characterized by a significant variability in eruption style and vent location. Densely inhabited cities are built on them and their surroundings, including the metropolitan areas of San Salvador (∼2.4 million people) and Managua (∼1.4 million people), respectively. In this study we present novel vent opening probability maps for these volcanic complexes, which are based on a multi-model approach that relies on kernel density estimators. In particular, we present thematic vent opening maps, i.e., we consider different hazardous phenomena separately, including lava emission, small-scale…
On the Volcanology of the West Eifel Maars
1987
The Quaternary alkali-basaltic volcanic field of the West Eifel is the classic maar region of the world. Related to the formation of the continental rift zone which extends through Central Europe, ultrabasic magmas rose from the upper mantle through the continental crust and fed 240 small volcanoes. Next to scoria cones with their lava flows, maars are most frequent and represent 25% of the volcanoes. Since 1820 and until 1970 their origin was mostly believed to be related to explosive exsolution of juvenile volatile phases. Since 1970, however, several authors have suggested that the West Eifel maars are phreatomagmatic in origin, i.e. rising magma contacted groundwater in near-surface lev…