Lake Nyos in dual agony-An assessment of the limnic eruption and dam collapse-

通过对尼奥斯湖湖沼喷发和尼奥斯马尔湖时代的地球化学研究，获得了以下结果。（1）Nyos湖和Monoun湖的岩浆CO_2积聚及其人工脱气：Nyos湖和Monoun湖一直被称为臭名昭著的火山口湖，因为它们在80年代中期突然爆炸，夺去了大约1800人的生命。自1986年以来的连续观测表明，两个湖泊不断地被地幔岩浆CO_2充注，导致溶解CO_2量的稳定增加，湖泊很可能再次发生湖沼喷发和随后的气体灾害。2001-2003年在各湖泊安装了人工脱气装置。然而，脱气速率不足以在几年内将气体含量降低到安全水平。因此，湖沼喷发的危险仍然存在。在这项研究中，我们估计了目前的天然气补给率， ...更多信息 和移除。在此基础上，我们模拟了湖泊CO_2含量随时间的变化。需要30多年的时间才能使尼奥斯湖安全。在目前的CO_2回灌-去除速率下，Monoun湖的气体含量将在几年内趋于稳定。幸运的是，2006年在Monoun湖安装了额外的脱气管道。如果排气管继续工作，Monoun湖将在不久的将来变得安全。尼奥斯湖仍然不安全。（2）尼奥斯湖大坝的年表：尼奥斯湖北端有一座45米高的天然大坝。大坝由在玛珥形成时沉积的固结不良的火山碎屑物质组成。有人认为，大坝是脆弱的，并已在高速率侵蚀，因为湖的形成。它可能在不久的将来崩溃。大坝倒塌将导致下游发生大规模洪水，并蔓延至尼日利亚。为了估计侵蚀速率，必须获得玛珥地层的可靠年龄。我们已经确定了年龄的大坝约。5000年B. P.使用U-Th-Ra测年法。这一年龄比用~（13）C法测得的400年要老得多<14>，比K-Ar法测得的约400 ka的年龄要年轻得多。我们的新时代将对大坝的侵蚀速度产生重要的限制。少

The following results have been obtained through this geochemical studies on the limnic eruption at Lake Nyos and the age of Lake Nyos maar.(1)Buildup_of_magmatic_CO_2_at_lakes_Nyos_and_Monoun_and_its_artificial_degassing : Lakes Nyos and Monoun have been known as notorious crater lakes, because they suddenly exploded in mid-80s, claiming about 1800 lives. Continuous observations since 1986 by the head investigator and his colleagues have demonstrated that the lakes are continuously charged by magmatic CO_2 of mantle origin, resulting in a steady increase in the amount of dissolved CO_2, and that recurrence of the limnic eruption followed by a gas disaster is highly likely at both lakes. Artificial degassing apparatus was installed at each lake in 2001-2003. However the degassing rate is not high enough to reduce the gas content to a safe level in several years. Thus danger of the recurrence of limnic eruption still remains.In this study, we estimated the current rates of gas recharge … More and removal. Based on the estimate we have modeled the change with time in the CO_2 content of the lakes. It will take more than 30 years to make Lake Nyos safe. At Lake Monoun the gas content would become steady within several years under the current CO_2 recharge-removal rates. Fortunately additional degassing pipes were installed at Lake Monoun in 2006. If degassing pipes keep working, Lake Monoun would become safe in the near future. Lake Nyos still remains unsafe.(2)Chronology of Lake Nyos dam : Lake Nyos is bound by a 45 m high natural dam at the north end. The dam consists of poorly consolidated pyroclastic materials that deposited at the time of the maar formation. It has been suggested that the dam is fragile and has been eroded away in a high rate since the formation of the lake. It may collapse in the near future. The dam collapse would result in a large scale flooding downstream which reaches Nigeria. In order to estimate the erosion rate, it is essential to obtain a reliable age of the maar formation. We have determined the age of the dam to be ca.5000 years B.P.using the U-Th-Ra dating method. This age is much older than 400 years obtained by the ^<14>C method and much younger than the K-Ar dates of ca.400 ka. Our new age would give an important constraint on the erosion rate of the dam. Less