Evolution of CO 2 Content in Lakes Nyos and Monoun, and Sub-lacustrine CO 2 -Recharge System at Lake Nyos as Envisaged from CO 2 / 3 He Ratios and Noble Gas Signatures
Evolution of CO 2 Content in Lakes Nyos and Monoun, and Sub-lacustrine CO 2 -Recharge System at Lake Nyos as Envisaged from CO 2 / 3 He Ratios and Noble Gas Signatures
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根据 CO 2 / 3 He 比率和惰性气体特征设想的尼奥斯湖和莫翁湖中 CO 2 含量的演变以及尼奥斯湖湖底 CO 2 补给系统
DOI：
10.1007/978-3-642-36833-2_19
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发表时间：
2015
期刊：
影响因子：
--
通讯作者：
M. Kusakabe
中科院分区：
文献类型：
--
作者：
M. Kusakabe
喀麦隆的尼奥斯湖和莫农湖被称为“杀手湖”，因为它们在80年代中期的一次天然气爆炸或湖泊喷发后造成约1,800人死亡，这是一次突然释放的二氧化碳，积聚在深水沃茨。这一事件吸引了国际科学界的兴趣，不仅是因为减灾，而且也是因为它在火山学上的重要意义。后续研究表明，两个湖泊深水中的二氧化碳浓度以惊人的速度增加，未来可能会发生天然气爆炸。为了避免再次发生爆炸，根据气体自升原理，使用管道对湖泊进行人工脱气。本章汇编了近25年来两湖的地球化学监测结果。将CO2剖面脱气前后的演化转化为湖泊CO2含量的时间变化，进而估算湖泊CO2的补给和去除速率。除气工作进展顺利，到2011年，莫农湖的二氧化碳排放量已达到最大排放量的90%以上，达到安全水平。由于该湖已经失去了气体自升能力，脱气将不再继续。在尼奥斯湖，脱气正在进行中，最大二氧化碳量的33%现已被去除。提出了天然气自发出溶模型。这一想法是基于1986年和2003年之间在莫诺湖CO2配置文件的时间变化。在此期间，剖面的演变相当稳定，即，深部富CO2层增厚，而CO2浓度保持不变。这表明，来自深处的补给流体具有与底层水相似的CO2浓度，并且它将最深的水向上推，导致富CO2层顶部的CO2饱和，从而导致1984年的湖沼喷发。就在2001年开始脱气操作之前，在尼奥斯湖观察到了类似的情况，即，深层富CO2层增厚，但其CO2浓度保持不变，约为350 mmol/kg，仍远低于CO2饱和度。在该湖泊中，脱气前的深水具有较低的CO2/3 He比值（~0.5 × 1010），而补给流体具有相对较高的CO2/3 He比值（~1.7 × 1010）。这表明，CO2和He在湖中的行为是解耦的。其补给流体可能是由具有较高的3 He/4 He、40 Ar/36 Ar、20 Ne/22 Ne和21 Ne/22 Ne比值的岩浆流体与具有空气同位素特征的地下水混合而成。
Lakes Nyos and Monoun in Cameroon are known as “killer lakes” because they killed ~1,800 people in the mid-80s after a gas explosion or limnic eruption, a sudden release of carbon dioxide accumulated in deep waters. This event attracted the interest of the international scientific community, not only for the sake of disaster mitigation but also for its volcanological significance. Follow-up studies indicated that the CO2concentration in deep water increased at an alarming rate at both lakes, and that a future gas explosion was likely to occur. To avoid recurrence of the explosion, artificial degassing of the lakes was set up using pipes based on the gas self-lift principle. This chapter compiles the results of the geochemical monitoring of the two lakes for the last 25 years. Pre- and syn-degassing evolution of CO2profiles was translated into the temporal changes of CO2content in the lakes, and thus estimate CO2recharge and removal rates. Degassing went on smoothly, and more than 90 % of the maximum amount of CO2was removed from Lake Monoun by 2011, reaching safe levels. Since the lake has lost its gas self-lift capability, degassing will no longer continue. At Lake Nyos, degassing is on-going and 33 % of the maximum amount of CO2has now been removed. A model of spontaneous gas exsolution is proposed. This idea is based on the temporal variation of CO2profiles at Lake Monoun between 1986 and 2003. During this period the profiles evolved rather steadily, i.e., the deep CO2-rich layer thickened while its CO2concentration remained constant. This suggests that the recharge fluid coming from depth had a CO2concentration similar to that of the bottom water, and that it pushed the deepest water upward, resulting in CO2saturation at the top of the CO2-rich layer, which led to the 1984 limnic eruption. A similar situation was observed at Lake Nyos just before the degassing operation started in 2001, i.e., the deep, CO2-rich layer thickened while its CO2concentration remained unchanged at about 350 mmol/kg, which is still far below CO2saturation. In this lake, pre-degassing deep water had low CO2/3He ratios (~0.5 × 1010), whereas the recharge fluid was characterized by relatively high CO2/3He ratios (~1.7 × 1010). This suggests that the behavior of CO2and He in the lake was decoupled. The recharge fluid is likely produced by mixing of magmatic fluids, which are characterized by relatively high3He/4He,40Ar/36Ar,20Ne/22Ne and21Ne/22Ne ratios, with groundwater having air isotopic signatures.
喀麦隆莫翁湖和尼奥斯湖受控脱气之前和期间 C0_2 的演变
DOI：
--
发表时间：
2008
期刊：
Geochemical Journal 42
影响因子：
--
作者：
M. Kusakabe;他
通讯作者：
他
影响因子：
3.9
作者：
Aka, FT;Nagao, K;Hell, J
通讯作者：
Hell, J