Temporal and spatial variations of CO2 diffuse volcanic degassing on Cuicocha Caldera Lake – Ecuador

SIERRA, DANIEL; VIGIDE, NICOLAS; NARVÁEZ, DIEGO F.; ALMEIDA, MARCO; PROAÑO, ANTONIO; HIDALGO, SILVANA; LAMBERTI, MARÍA CLARA; SIERRA, DANIEL; VIGIDE, NICOLAS; NARVÁEZ, DIEGO F.; ALMEIDA, MARCO; PROAÑO, ANTONIO; HIDALGO, SILVANA; LAMBERTI, MARÍA CLARA

JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH

ELSEVIER SCIENCE BV

Año: 2020

0377-0273

Cuicocha Caldera is the youngest eruptive center of Cotacachi-Cuicocha Volcanic Complex, located at the northof Ecuador. The caldera contains a lake of 3.95 km2 surface, and a maximum depth of 148 m. Cuicocha Lake ischaracterized by the presence of CO2 gaseous diffuse emissions, perceptible as bubbling zones. Since 2011, CO2diffuse flux measurements have been performed in this lake using the accumulation chamber method. The dataobtained from twenty surveys were processed by means of the Graphical Statistical Approach and the SequentialGaussian Simulation. The results reveal that Cuicocha lake has released a total estimated amount of ~400 ktof CO2 in the period between March 2011 and May 2019, with an average rate of 135 t/day. Furthermore, thespatial and temporal analysis of the data made possible the understanding of the processes occurring in the lake:1) Lake stratification caused by the seasons seem to favor CO2 accumulation in the hipolimnion and its posteriorreleasing. Minimum total flux values of ~50 t/day have been estimated during ?warm? stratified periods andmaximum flux values of ~170 t/day have been recorded during ?cold? overturn periods. Additionally, at leasttwo anomalous degassing episodes were identified in 2012?2013, seemingly associated to changes in the volcanicactivity also detected through seismicity. 2) Cuicocha CO2 degassing seems to be controlled by the existence ofdiffuse degassing structures at the lake bottom, which correspond to high permeability zones resulting from theintersection between ~NE-SW and ~WNW-ESE oriented structures. We propose a conceptual model to explainthe systematic apparition of CO2 anomalies on specific areas of the lake surface.