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| Titel |
Cotopaxi volcano's unrest and eruptive activity in 2015: mild awakening after 73 years of quiescence |
| VerfasserIn |
Silvana Hidalgo, Benjamin Bernard, Jean Battaglia, Elizabeth Gaunt, Charlotte Barrington, Daniel Andrade, Patricio Ramon, Santiago Arellano, Hugo Yepes, Antonio Proaño, Stefanie Almeida, Daniel Sierra, Florian Dinger, Peter Kelly, René Parra, Nicole Bobrowski, Bo Galle, Marco Almeida, Patricia Mothes, Alexandra Alvarado |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250125460
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| Publikation (Nr.) |
 EGU/EGU2016-5043.pdf |
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| Zusammenfassung |
| Cotopaxi volcano (5,897 m) is located 50 km south of Quito, the capital of Ecuador. The most
dangerous hazards of this volcano are the devastating lahars that can be generated by the
melting of its ice cap during pyroclastic flow-forming eruptions. The first seismic station was
installed in 1976. Cotopaxi has been monitored by the Instituto Geofísico (Escuela
Politécnica Nacional) since 1983. Presently the monitoring network is comprised of 11
broadband and 5 short period seismometers, 4 scanning DOAS, 1 infrared and 5 visible
cameras, 7 DGPS, 5 tiltmeters, 11 AFM (lahar detectors) and a network of ashmeters. Due to
the recent unrest, the monitoring of the volcano has been complemented by campaign
airborne Multi-GAS and thermal IR measurements and ground-based mobile DOAS and
stationary solar FTIR.
After 73 years of quiescence, the first sign of unrest was a progressive increase in the
amplitude of transient seismic events in April 2015. Since May 20, an increase in SO2
emissions from ∼500 t/d to ∼3 kt/day was detected followed by the appearance of seismic
tremor on June 4. Both SO2 emissions of up to 5 kt/day and seismic tremor were observed
until August 14 when a swarm of volcano-tectonic earthquakes preceded the first phreatic
explosions. These explosions produced ash and gas columns reaching up to 9 km above the
crater. The ash fall produced by the opening phase covered over 500 km2 with a
submillimetric deposit corresponding to a mass of 1.65E+8 kg (VEI 1). During this period of
explosions, SO2 emission rates up to 24 kt/day were observed, the highest thus far. The ash
was dominantly hydrothermally altered and oxidized lithic fragments, hydrothermal minerals
(alunite, gypsum), free crystals of plagioclase and pyroxenes, and little juvenile
material.
Unrest continued after August 14, with three episodes of ash emission. However, the
intensity of ash fallout, average seismic amplitude, and SO2 emissions during each
successive episode progressively decreased, while juvenile component increased.
Total ash fallout mass since August 14 yield 1.19E+9 kg. During these episodes
BrO and HCl were detected in the plume, and airborne Multi-GAS measurements
showed that the plume had a CO2/SO2 ratio from 1 to 2.5 and that SO2 was >99% of
total sulfur (SO2+ H2S), indicating a shallow magmatic origin for the gas. During
ash emissions temperatures of up to 200º C were measured at the column with
an IR camera. Thermal anomalies in the upper part of the edifice have also been
observed and have resulted in minor melting of the ice cap. This phenomenon has
produced small secondary lahars with a maximum discharge on the order of 10 to 30
m3/s.
Since late November 2015, surface manifestations and the other monitored parameters have
shown a marked decrease. Historical reports of Cotopaxi’s activity show that both
short and long-lasting eruptive periods usually start with mild eruptive phases prior
to culminating in VEI 3 or 4 eruptions. Therefore special care should be taken
in monitoring unrest at Cotopaxi in order to identify precursory signs of a larger
eruption. |
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