Sangay volcano (Ecuador): multiparametric analysis of the December 2021 eruptive activity including the opening of new vents, a drumbeat seismic sequence and a new lava flow
Silvana HidalgoFrancisco J. VasconezJean BattagliaBenjamin BernardPedro EspínSébastien ValadeMaria-Fernanda NaranjoRobin CampionJosue SalgadoMarco CórdovaMarco AlmeidaStephen HernándezGerardo PinoElizabeth GauntAndrew BellPatricia MothesMario RuizS. Daniel Andrade
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Abstract:
Sangay is a 5286 m high stratovolcano located in the southern part of the Ecuadorian Andes, about 200 km south of the capital city of Quito. Sangay is the last active volcano to the south of the Northern Andes, and has been characterized by an almost constant and continuous activity with variable periods of quiescence. During historical times, the written reports describe at least 9 major eruptions since 1628. Sangay has been instrumentally monitored by the Instituto Geofísico of the Escuela Politécnica Nacional (IG-EPN) since 2013. In May 2019, Sangay began a new eruptive period, which is still ongoing and has been categorized as the most intense in the last six decades. The main phenomena produced during this period are small explosions, ash and gas emissions, lava fountaining, lava flows and associated pyroclastic currents and secondary lahars.On 1 December 2021, from around 19:20 UTC, the seismic recordings of SAGA station began to show transient events occurring regularly. These events persisted for the next 13 hours with an irregularly accelerating rate of occurrence and increasing amplitude before merging into tremor at around 08:20 on 2 December. This sequence was rapidly followed by two explosive emissions, which were observed by the GOES-16 satellite, the first one at 09:02 and the second at 09:13. The emissions produced a 14.5 km-high gas-rich, ash-depleted eruptive column without any associated regional fallout reported. This drumbeat sequence was produced after a series of morphological changes observed through satellite images (Planet and Sentinel 2). Specifically, during the short time period considered in this study: 1) two new vents opened; 2) a landslide affected the northern flank of the volcano; 3) the first drumbeat sequence was recorded at Sangay; and 4) a new lava flow was emitted through the new northern vent. The drumbeat sequence is interpreted as being caused by the forced extrusion of this new lava flow through the new opening northern vent. Timely communication of this kind of volcanic events is favored by the creation and strict following of internal protocols within volcano observatories and the appropriate use of social networks allowing thousands of people to be reached in very short time period. The corresponding short report produced by the IG-EPN reached more than 300.000 people.Keywords:
Stratovolcano
Lahar
Sequence (biology)
Each of the three phases of the 2006 eruption at Augustine Volcano had a distinctive eruptive style and flowage deposits. From January 11 to 28, the explosive phase comprised short vulcanian eruptions that punctuated dome growth and produced volcanowide pyroclastic flows and more energetic hot currents whose mobility was influenced by efficient mixing with and vaporization of snow. Initially, hot flows moved across winter snowpack, eroding it to generate snow, water, and pyroclastic slurries that formed mixed avalanches and lahars, first eastward, then northward, and finally southward, but subsequent flows produced no lahars or mixed avalanches. During a large explosive event on January 27, disruption of a lava dome terminated the explosive phase and emplaced the largest pyroclastic flow of the 2006 eruption northward toward Rocky Point. From January 28 to February 10, activity during the continuous phase comprised rapid dome growth and frequent dome-collapse pyroclastic flows and a lava flow restricted to the north sector of the volcano. Then, after three weeks of inactivity, during the effusive phase of March 3 to 16, the volcano continued to extrude the lava flow, whose steep sides collapsed infrequently to produce block-and-ash flows. The three eruptive phases were each unique not only in terms of eruptive style, but also in terms of the types and morphologies of deposits that were produced, and, in particular, of their lithologic components. Thus, during the explosive phase, low-silica andesite scoria predominated, and intermediate- and high-silica andesite were subordinate. During the continuous phase, the eruption shifted predominantly to high-silica andesite and, during the effusive phase, shifted again to dense low-silica andesite. Each rock type is present in the deposits of each eruptive phase and each flow type, and lithologic proportions are unique and consistent within the deposits that correspond to each eruptive phase. The chief factors that influenced pyroclastic currents and the characteristics of their deposits were genesis, grain size, and flow surface. Column collapse from short-lived vulcanian blasts, dome collapses, and collapses of viscous lavas on steep slopes caused the pyroclastic currents documented in this study. Column-collapse flows during the explosive phase spread widely and probably were affected by vaporization of ingested snow where they overran snowpack. Such pyroclastic currents can erode substrates formed of snow or ice through a combination of mechanical and thermal processes at the bed, thus enhancing the spread of these flows across snowpack and generating mixed avalanches and lahars. Grain-size characteristics of these initial pyroclastic currents and overburden pressures at their bases favored thermal scour of snow and coeval fluidization. These flows scoured substrate snow and generated secondary slurry flows, whereas subsequent flows did not. Some secondary flows were wetter and more laharic than others. Where secondary flows were quite watery, recognizable mixed-avalanche deposits were small or insignificant, and lahars were predominant. Where such flows contained substantial amounts of snow, mixed-avalanche deposits blanketed medial reaches of valleys and formed extensive marginal terraces and axial islands in distal reaches. Flows that contained significant amounts of snow formed cogenetic mixed avalanches that slid across surfaces protected by snowpack, whereas water-rich axial lahars scoured channels. Correlations of planimetric area (A) versus volume (V) for pyroclastic deposits with similar origins and characteristics exhibit linear trends, such that A=cV2/3, where c is a constant for similar groups of flows. This relationship was tested and calibrated for dome-collapse, column-collapse, and surgelike flows using area-volume data from this study and examples from Montserrat, Merapi, and Mount St. Helens. The ratio A/V2/3=c gives a dimensionless measure of mobility calibrated for each of these three types of flow. Surgelike flows are highly mobile, with c≈520; column-collapse flows have c≈150; and dome-collapse flows have c≈35, about that of simple rock avalanches. Such calibrated mobility factors have a potential use in volcano-hazard assessments.
Lava dome
Stratovolcano
Peléan eruption
Lahar
Effusive eruption
Pyroclastic fall
Phreatic eruption
Phreatomagmatic eruption
Scoria
Dome (geology)
Strombolian eruption
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Phreatomagmatic eruption
Lahar
Lapilli
Peléan eruption
Caldera
Volcanic hazards
Pyroclastic fall
Maar
Cite
Citations (50)
Stratovolcano
Pyroclastic fall
Massif
Peléan eruption
Chronology
Caldera
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Misti volcano in southern Peru has a record of explosive eruptions and a nearby population of over 810,000, making it a hazardous volcano. The city center of Arequipa, Peru's second most populous city, is 15 km from the summit of Misti, and many neighborhoods are closer. As the population increases yearly, the urban boundary continues to move up the south side of the volcano. Many parts of the city are built upon the deposits from Misti's most recent Plinian eruption at ca. 2 ka. The 2 ka Plinian eruption (Volcanic Explosivity Index [VEI] 5) produced a 1.4 km3 tephra-fall deposit and 0.01 km3 of pyroclastic-flow deposits in ~2–5 h. Column height varied during the eruption but ascended up to 29 km. Pyroclastic flows descended only the south side of the volcano. The tephra fall spread southwest, resulting in ~20 cm of tephra accumulation in the area now occupied by the city center. The flowage deposits were previously identified as pyroclastic-flow deposits, but new sedimentologic and textural evidence suggests that ~80% (by volume) of the deposits were emplaced wet and relatively cold. As such, they are lahar deposits. A Neoglacial advance concurrent with the eruption supports evidence for voluminous snow and ice on the edifice. Pyroclastic flows melted between 0.01 km3 and 0.04 km3 of ice and snow on the volcano, triggering lahars that descended the volcano and inundated channels and some interfluves on the south flank. The lahars evolved downstream from proximal debris flows to distal hyperconcentrated flows, emplacing ~0.04 km3 of deposits. Four facies of lahar deposits are present in the channels and another facies occurs on the interfluves.
Lahar
Peléan eruption
Pyroclastic fall
Phreatic eruption
Phreatomagmatic eruption
Volcanic hazards
Dense-rock equivalent
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Myoko volcano, situated in the northern part of Central Japan, is one of the composit stratovolcanoes whose life histories have been studied in detail. In this paper, ten volcanic ash layers belonging to the central cone stage of Myoko volcano are described, and more detailed volcanic history of the central cone stage is compiled in connection with the informations already known.The result are summarized as follows:(1) The central cone stage started ca. 5, 800 years ago. The central cone, Mt. Myoko, was almost built at the early time of the stage.(2) The youngest magmatic eruption of Myoko volcano took place ca. 4, 200 years ago, and produced pyroclastic flows and pyroclastic surges.(3) The youngest steam explosion of Myoko that was confirmed took place ca. 3, 000 years ago, and produced small pyroclastic surges.(4) For 1, 600 years between 5, 800 and 4, 200 years ago, a series of eruption whose ejecta were kept as an obvious stratum at the foot of Myoko volcano took place at the average rate of once for 200 or 300 years. After the violent eruption of ca. 4, 200 years ago, Myoko rapidly became less active, and the eruption in the similar scale took place only once or twice for ca. 4, 200 years up to the present.(5) The central cone stage was dominated mainly by the activity of dacitic magma, and coincided with the time when pyroclastic flows and pyroclastic surges were apt to be produced by explosive eruptions.
Stratovolcano
Pyroclastic fall
Peléan eruption
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Merapi volcano as one of most active strato-volcano tipes in the world, at the
historical of the eruption had some different types of eruptions, as explosive and effusive
eruption. Effusive type of eruption creates lava spills, lava dome and pyroclastic
avalanches while explosive eruption leads to pyroclastic falls and pyroclastic flow.
Lahar is type of mudflow composed of debris and angular block mostly from a
volcano. In Mt. Merapi, lahars can affect the people widely, causing not only loss of lives
but also damage and loss of property and livelihood assets.
The morphological features of Merapi Volcano consist of four slopes that are
bordered by slope breaks. Each slope and slope break are reflecting their dominant rocks
formation, their morphological functions to the volcanic deposits, and past historical
processes.
Based on its characteristics of explosive and effusive eruptions as well as
processes of lahar flows, Mt. Merapi is formed by five units of lava, four pyroclastics and
five units of lahars. The stratigraphy of Merapi Volcano can be ctagorised into 5 stages:
New Merapi, Young Merapi Mature Merapi, Old Merapi, and Pre Merapi.
In adherence to the post positivism paradigm that requires verification and/or
validation of the probabilistic approaches through parametric as well as non-parametric
statistical tests, it profess that Mt. Merapi during the Neogene period experienced
evolution of types eruption. The main chemical compositions TiO2, Fe2O3, MgO, CaO,
and K2O as well as the rims of hornblende structure distinguish the types of eruptions
during that period. Changes of pyroclastic character are determined by the gigness and
forms of components in the sizes of block, pebbles and gravels, not by giant component.
The changes in sizes and forms of pyroclastic components are not in order and not in
correlation with the distance of deposits. Lahar characters change in oderly
fashion,(negatively) in medium to very strong correlation with the distance of deposits.
The correlations get stronger during the lahar flow in the one watershed; meanwhile , the
forms of lahar components are not in oderly fashion and not in correlation with the
distance of sediment deposits.
Giant component is constitutes the main significant part to be managed in the
adaptation of lahar risk reduction. For that purpose, a research on the geology of
volcano with the further details analysis on lahar components is highly necessary. The
positions of lahar as the responses to types of eruptions become a significant part in the
efforts in developing a geological map, distater prone zone map as well as Merapi
eruption disaster risk map. The method can subsequently be applicable for mapping of
other volcanoes
Kata Kunci/ Key-words: Merapi. Lahar, post-positivism
Lahar
Volcanic hazards
Lava dome
Effusive eruption
Peléan eruption
Stratovolcano
Mudflow
Phreatic eruption
Maar
Dense-rock equivalent
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