Provider: - Institution: - Data provided by Europeana Collections- In our weekly paragraph, we meet the wishes of our viewers to get to know different places in Europe, and today we meet the desire ...of scenes from Ecuador to send us a message asking to identify the Greek island of Santorini, located in the Aegean Sea in the southeast of the country.- ضمن فقرتنا الاسبوعية أمنيات شخصية والتي من خلالها نلبي رغبات مشاهدينا في التعرف على أماكن مختلفة في أوروبا، واليوم نلبي رغبة مشاهد من الإكوادور أرسل لنا رسالة يطلب فيها التعرف على جزيرة سانتوريني اليونانية التي تقع في بحر إيجا جنوب شرق البلاد.- All metadata published by Europeana are available free of restriction under the Creative Commons CC0 1.0 Universal Public Domain Dedication. However, Europeana requests that you actively acknowledge and give attribution to all metadata sources including Europeana
Caldera-forming volcanic eruptions are low-frequency, high-impact events capable of discharging tens to thousands of cubic kilometres of magma explosively on timescales of hours to days, with ...devastating effects on local and global scales. Because no such eruption has been monitored during its long build-up phase, the precursor phenomena are not well understood. Geophysical signals obtained during recent episodes of unrest at calderas such as Yellowstone, USA, and Campi Flegrei, Italy, are difficult to interpret, and the conditions necessary for large eruptions are poorly constrained. Here we present a study of pre-eruptive magmatic processes and their timescales using chemically zoned crystals from the 'Minoan' caldera-forming eruption of Santorini volcano, Greece, which occurred in the late 1600s BC. The results provide insights into how rapidly large silicic systems may pass from a quiescent state to one on the edge of eruption. Despite the large volume of erupted magma (40-60 cubic kilometres), and the 18,000-year gestation period between the Minoan eruption and the previous major eruption, most crystals in the Minoan magma record processes that occurred less than about 100 years before the eruption. Recharge of the magma reservoir by large volumes of silicic magma (and some mafic magma) occurred during the century before eruption, and mixing between different silicic magma batches was still taking place during the final months. Final assembly of large silicic magma reservoirs may occur on timescales that are geologically very short by comparison with the preceding repose period, with major growth phases immediately before eruption. These observations have implications for the monitoring of long-dormant, but potentially active, caldera systems.
The Minoan eruption of Santorini is one of the largest Holocene volcanic events and produced several cubic kilometers of pyroclastic flows emplaced on the submerged flanks of the volcano. Marine ...geophysical surveys reveal a multitude of undulating seafloor bedforms (USBs) around Santorini. While similar structures are known from other volcanoes worldwide, Santorini offers the unique opportunity to relate USB formation with volcanic processes during one of the best-studied volcanic eruptions worldwide. In this study, we combine high-resolution seismic reflection data with multibeam echosounder bathymetry to reveal the internal architecture of USBs around Santorini and to relate their morphological characteristics to formational processes. The USBs around Santorini were formed during the Minoan eruption and represent the seafloor expression of mass transport deposits. Three types of deposits differ in composition or origin. (1) Depositional USBs, which can only be found to the north of the island, where Minoan eruption ignimbrites reach their maximum thickness and the undulating topography is the result of thrusting within the deposit. (2) USBs related to slope failures of volcaniclastics from the entire Thera Pyroclastic Formation, which can be found east, south, and west of the island. (3) USBs associated with deep-seated deformation, which occurs on the southwestern flank along an area affected by rift tectonics and extends to a depth of more than 200 m below the seafloor. In cases (2) and (3), the USBs are formed upslope by block rotation and downslope by thrusting. Our study indicates that these processes may have contributed to the generation of the devastating Minoan tsunami. Since Santorini is located in one of the most tectonically active regions in the Mediterranean, capable of producing earthquakes with magnitude M7+, our study has important implications for hazard assessment. A strong earthquake located close to the island may have the potential to reactivate slope instabilities posing a previously undetected but potentially significant tsunami hazard.
•The Minoan eruption formed undulating seafloor bedforms (USBs) around Santorini.•USBs are the result of pyroclastic flows, slope failure and deep-seated deformation.•Deep-seated deformation affects the southwestern flank of Santorini.
Crustal magma chambers can grow to be hundreds to thousands of cubic kilometers, potentially feeding catastrophic caldera‐forming eruptions. Smaller volume chambers are expected to erupt frequently ...and freeze quickly; a major outstanding question is how magma chambers ever grow to the sizes required to sustain the largest eruptions on Earth. We use a thermo‐mechanical model to investigate the primary factors that govern the extrusive:intrusive ratio in a chamber, and how this relates to eruption frequency, eruption size, and long‐term chamber growth. The model consists of three fundamental timescales: the magma injection timescale τin, the cooling timescale τcool, and the timescale for viscous relaxation of the crust τrelax. We estimate these timescales using geologic and geophysical data from four volcanoes (Laguna del Maule, Campi Flegrei, Santorini, and Aso) to compare them with the model. In each of these systems, τin is much shorter than τcool and slightly shorter than τrelax, conditions that in the model are associated with efficient chamber growth and simultaneous eruption. In addition, the model suggests that the magma chambers underlying these volcanoes are growing at rates between ~10−4 and 10−2 km3/year, speeding up over time as the chamber volume increases. We find scaling relationships for eruption frequency and size that suggest that as chambers grow and volatiles exsolve, eruption frequency decreases but eruption size increases. These scaling relationships provide a good match to the eruptive history from the natural systems, suggesting that the relationships can be used to constrain chamber growth rates and volatile saturation state from the eruptive history alone.
Plain Language Summary
Magma chambers in the Earth's crust grow by incremental addition of new magma from deeper reservoirs, and over time can reach volumes that would fill the entire Grand Canyon. However, small magma chambers in the earliest stages of formation are prone to frequent eruptions and will lose heat quickly to the surrounding crust, both of which supposedly impede growth. Therefore, an important question is how magma chambers can possibly grow to such large sizes. Here we present results of physics‐based modeling aimed at understanding what conditions allow magma chambers to grow. We test effects of chamber size, rate of magma supply, water content in the magma, and plasticity of the crust hosting the chamber. Results suggest that growth is promoted when chambers cool slowly and are hosted within pliable crust that can easily relax pressures that build within the chamber. Surprisingly, we found that for a particular range of crustal pliability, growth is accompanied by frequent volcanic eruptions. We compared these results to four large volcanoes in Chile, Italy, Greece, and Japan. Model predictions for eruption frequency and chamber growth rates are a good match to what we observe at these volcanoes from the rock record and active monitoring systems.
Key Points
Coupled thermo‐mechanical modeling suggests that magma chambers grow when recharge and viscous relaxation of the crust are fast compared to chamber cooling
Magma chambers containing exsolved volatiles may shrink over time despite constant recharge because high magma compressibility leads to large eruption volumes
Eruptive phases at Laguna del Maule, Campi Flegrei, Santorini, and Aso reflect growth of chambers; amount of growth can be estimated from eruption frequency and size
We use the tephrostratigraphic framework along the Aegean Volcanic Arc established in Part 1 of this contribution to determine hemipelagic sedimentation rates, calculate new tephra ages, and ...constrain the minimum magnitudes of (sub)plinian eruptions of the last 200 kyrs. Hemipelagic sedimentation rates range from ∼0.5 cm/kyr up to ∼40 cm/kyr and vary laterally as well as over time. Interpolation between dated tephras yields an eruption age of ∼37 ka for the Firiplaka tephra, showing that explosive volcanism on Milos is ∼24 kyrs younger than previously thought. The four marine Nisyros tephras (N1 to N4) identified in Part 1 (including the Upper (N1) and Lower (N4) Pumice) have ages of ∼57 ka, ∼63 ka, ∼69 ka, and ∼76 ka, respectively. Eruption ages for the Yali‐1 and Yali‐2 tephras are ∼55 ka and ∼34 ka, respectively. The Yali‐2 tephra comprises two geochemically and laterally distinct marine facies. The southern facies is identical to the Yali‐2 fall deposit on land but the western facies has slightly less evolved glass compositions. Overall, erupted plinian and co‐ignimbrite fall tephra volumes range from <1 to 56 km3 (excluding possible caldera fillings and ignimbrite volumes), and 80% of the eruptions had magnitude 5.5 < M ≤ 7.2 (M = log(m)‐7; m = erupted magma mass in kg). Twenty percent of the tephras represent 3.2 < M < 5.5 eruptions. The long‐term average tephra magma mass flux through highly explosive eruptions of Santorini is estimated at ∼40 kg/s. The analogous data for the Kos‐Yali‐Nisyros volcanic complex is less‐well constrained but similar to Santorini.
Plain Language Summary
Sediment cores from the seafloor of the eastern Aegean Sea contain numerous ash layers from (sub)plinian eruptions from the Aegean Volcanic Arc that were correlated in Part 1. These correlations facilitate determination of sedimentation rates of ∼0.5–∼40 cm/kyr within the hemipelagic sediment bracketing the dated tephras. Sedimentation rates show temporal and lateral variations in the context of climate changes, and regional tectonics. Exceptionally high hemipelagic sedimentation rates within the last 4 kyrs, are linked to the 3.6 ka Minoan and the 1650 AD Kolumbo eruptions that emplaced abundant erodible tephra. Using the sedimentation rates we additionally determine the ages of hitherto undated tephras. We deduce an age of ∼37 ka for a Milos eruption, as well as ∼57 ka to ∼76 ka for marine Nisyros and ∼34 and ∼55 ka for Yali tephras, for which previous dating attempts yielded controversial ages. The ash distribution in the marine realm of up to 105 km2 represents a major fraction of the erupted tephra volumes that range from <1 to 56 km3, placing 60% of the investigated eruptions into magnitude category M6, 20% into M7, and 20% into M3 to M5 classes. Over the past ∼200,000 years, Santorini discharged magmas at an average rate of ∼40 kg/s.
Key Points
Tephrochronology for the Aegean Arc eruptions
Sedimentation rate variability in the Aegean Sea
Eruptive volumes and masses for the major Aegean Arc eruptions
Hydrothermal experiments were conducted to determine the partitioning of Cl between rhyolitic to rhyodacitic melts, apatite, and aqueous fluid(s) and the partitioning of F between apatite and these ...melts at ca. 200
MPa and 900–924
°C. The number of fluid phases in our experiments is unknown; they may have involved a single fluid or vapor plus saline liquid. The partitioning behavior of Cl between apatite and melt is non-Nernstian and is a complex function of melt composition and the Cl concentration of the system. Values of
D
Cl
apat/melt (wt. fraction of: Cl in apatite/Cl in melt) vary from 1 to 4.5 and are largest when the Cl concentrations of the melt are at or near the Cl-saturation value of the melt. The Cl-saturation concentrations of silicate melts are lowest in evolved, silica-rich melts, so with elevated Cl concentrations in a system and with all else equal, the maximum values of
D
Cl
apat/melt occur with the most felsic melt. In contrast, values of
D
F
apat/melt range from 11 to 40 for these felsic melts, and many of these are an order of magnitude greater than those applying to basaltic melts at 200
MPa and 1066–1150
°C. The Cl concentration of apatite is a simple and linear function of the concentration of Cl in fluid. Values of
D
Cl
fluid/apat for these experiments range from 9 to 43, and some values are an order of magnitude greater than those determined in 200-MPa experiments involving basaltic melts at 1066–1150
°C.
In order to determine the concentrations and interpret the behavior of volatile components in magmas, the experimental data have been applied to the halogen concentrations of apatite grains from chemically evolved rocks of Augustine volcano, Alaska; Krakatau volcano, Indonesia; Mt. Pinatubo, Philippines; Mt. St. Helens, Washington; Mt. Mazama, Oregon; Lascar volcano, Chile; Santorini volcano, Greece, and the Bishop Tuff, California. The F concentrations of these magmas estimated from apatite–melt equilibria range from 0.06 to 0.12
wt% and are generally equivalent to the concentrations of F determined in the melt inclusions. In contrast, the Cl concentrations of the magmas estimated from apatite–melt equilibria (e.g., ca. 0.3–0.9
wt%) greatly exceed those determined in the melt inclusions from all of these volcanic systems except for the Bishop Tuff where the agreement is good. This discrepancy in estimated Cl concentrations of melt could result from several processes, including the hypothesis that the composition of apatite represents a comparatively Cl-enriched stage of magma evolution that precedes melt inclusion entrapment prior to the sequestration of Cl by coexisting magmatic aqueous and/or saline fluid(s).
Santorini volcanic complex (Greece) is the result of a long evolutionary history, marked by the alternation of explosive (Plinian) eruptions and interplinian low explosive/effusive eruptive cycles. ...Products emitted during the interplinian stages are well exposed along the rim of the calderic structure formed during the major Minoan (3.6 ka) Plinian eruption. We conducted a systematic sampling of the basaltic to dacitic lavas erupted by the interplinian volcanic centre of Skaros, active between 67 and 54 ka. The continuously exposed products of the Skaros lifecycle offer the tremendous opportunity to reconstruct the petrological evolution of the volcanic centre, and in turn to provide new insights on the behaviour of Santorini feeding system during interplinian stages. The combination of whole-rock, mineral chemistry and synchrotron X-ray computed microtomography analyses enabled us to decipher the main physico-chemical parameters of the Skaros plumbing system that drove ascent and differentiation processes of magmas. Results indicate that the main magma ponding zone beneath Skaros centre extended from 12 to 4 km b.s.l., where it underwent frequent refilling by basaltic melts. In the later evolutionary stage of the Skaros system, the basaltic replenishment became less frequent allowing the ultimate differentiation of magma towards dacitic composition. The shallow nature of the magma ponding zone, sited well above the H2O saturation depth, favoured the continuous degassing and inhibited the increase of vapor pressure during differentiation, preventing the onset of explosive eruptions, as in case of the major explosive events at Santorini.
•Skaros volcano (Santirini) inter-Plinian effusive activity products were investigated.•The polybaric plumbing system was frequently fed by basaltic melts at early stages.•Magma feeding decreased in the late stage of the volcano activity.•Emitted lavas evolved towards more acidic composition.•Shallow depth of ponding zones favoured degassing, preventing explosive eruptions.
Volcanic eruptions are driven by magma rising through Earth’s crust. The style of an eruption depends on intrinsic and extrinsic parameters and is commonly a dynamic process. Thorough and holistic ...investigation of the related products is key to understanding eruptive phenomena and assessment of volcano-specific hazards. Models of such phenomena are constrained by quantification of the dispersal, the grain size distribution, and pyroclast textures. Pyroclast texture may be described in part by measurements of density and porosity, which depend on pyroclast volume determination. Yet volume determination of irregularly shaped pyroclasts cannot be achieved with geometrical laws, instead necessitating the use of alternative methodologies. Here, we test three methodologies to quantify pyroclast volume on a set of clasts collected from the Minoan eruption deposits from Santorini, Greece. We compare (1) a manual method for obtaining the lengths of three orthogonal axes of the pyroclast with a caliper, (2) an optical method to measure the longest and shortest axes of the pyroclast via multiple photographs, and (3) an Archimedean buoyancy-based method. While the optical and manual methods provide almost identical values of pyroclast volume when tested under laboratory conditions, there is a discrepancy between these two methods and the Archimedean method, which produces an overestimation of ca. 13% in volume. This discrepancy has little impact on the subsequent assessment of porosity and density for which the natural variability of values is observed to be broader. We therefore propose using the manual approach in the field as a simple and fast, yet reliable, method to obtain large volumes of quantitative data on the texture of erupted products, and we also provide a correction factor for in-field volume assessment of rhyodacitic pumices.
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