Abstract Cuicocha Caldera is the youngest eruptive center of Cotacachi-Cuicocha Volcanic Complex, located at the north of Ecuador. The caldera contains a lake of 3.95 km2 surface, and a maximum depth of 148 m. Cuicocha Lake is characterized by the presence of CO2 gaseous diffuse emissions, perceptible as bubbling zones. Since 2011, CO2 diffuse flux measurements have been performed in this lake using the accumulation chamber method. The data obtained from twenty surveys were processed by means of the Graphical Statistical Approach and the Sequential Gaussian Simulation. The results reveal that Cuicocha lake has released a total estimated amount of ~400 kt of CO2 in the period between March 2011 and May 2019, with an average rate of 135 t/day. Furthermore, the spatial 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 posterior releasing. Minimum total flux values of ~50 t/day have been estimated during “warm” stratified periods and maximum flux values of ~170 t/day have been recorded during “cold” overturn periods. Additionally, at least two anomalous degassing episodes were identified in 2012–2013, seemingly associated to changes in the volcanic activity also detected through seismicity. 2) Cuicocha CO2 degassing seems to be controlled by the existence of diffuse degassing structures at the lake bottom, which correspond to high permeability zones resulting from the intersection between ~NE-SW and ~WNW-ESE oriented structures. We propose a conceptual model to explain the systematic apparition of CO2 anomalies on specific areas of the lake surface.

中文翻译：

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厄瓜多尔库科查火山口湖 CO2 扩散火山脱气的时空变化

摘要 Cuicocha Caldera 是Cotacachi-Cuicocha 火山群最年轻的喷发中心，位于厄瓜多尔北部。火山口包含一个面积为3.95 km2 的湖泊，最大深度为148 m。Cuicocha 湖的特点是存在二氧化碳气体扩散排放，可感知为冒泡区。自 2011 年以来，已使用累积室方法在该湖中进行 CO2 扩散通量测量。通过图形统计方法和序列高斯模拟处理从 20 次调查中获得的数据。结果显示，2011 年 3 月至 2019 年 5 月期间，库科查湖共排放了约 400 kt 的 CO2，平均排放量为 135 t/天。此外，数据的空间和时间分析使了解湖泊中发生的过程成为可能：1) 由季节引起的湖泊分层似乎有利于 CO2 在海洋中的积累及其后释放。在“暖”分层期间估计的最小总通量值约为 50 吨/天，在“冷”倾覆期记录的最大通量值约为 170 吨/天。此外，在 2012-2013 年至少发现了两次异常脱气事件，似乎与通过地震活动检测到的火山活动变化有关。2) Cuicocha CO2 脱气似乎受湖底扩散脱气结构的控制，这对应于~NE-SW 和~WNW-ESE 定向结构之间的交叉点产生的高渗透区。