Nyiragongo and Nyamuragira are two active volcanoes of the Western branch of the East African Rift in the Virunga area. They were built at the Kivu rift axis ca. 12,000 years ago and set above two tectonic steps separated by the Kameronze Fault. Both volcanoes have displayed a succession of intra-crater and flank eruptions that have been observed and documented since the end of the nineteenth century. Here, we have collated and reviewed these publications and reports. Nyiragongo is famous for its semi-permanently active lava lake, which at the time of writing (2020) was the largest in the world. During the construction of the main stratovolcano, which ended a few centuries ago with a caldera collapse, the lava composition changed from melilitite to leucite and then to melilite-bearing nephelinite. The historically active lava lake is believed to be directly fed from an upper intra-volcano reservoir, a shallow reservoir situated a few kilometres below the volcano in the granite basement, and a deeper intra-crustal magma chamber. Historic activity has been documented since 1894 and can be divided into eight stages, on the basis of sudden changes between lava filling and draining, with cycles of rising lava lake activity and overflows, followed by sinking and complete or partial drainage. Twice in recent history (in 1977 and 2002), major flank eruptions were accompanied by complete drainage of the lava lake and the upper plumbing system. The lava that filled the crater since 1948, and then again after the 1977 and 2002 drainage events have been calculated at a cumulative volume of around 324 × 10 6 m 3 . In comparison, the 1977 and 2002 flank eruptions involved 47 × 10 6 m 3 of lava. The average annual output rate associated with crater filling is thus estimated at between 4 and 13 × 10 6 m 3 . Lava lake behaviour changes from equilibrium, with alternation between gas pistoning and spattering regimes through disequilibrium with intermittent activity, to complete disappearance of the lava lake. These changes can be related to the conditions of the descent of dense degassed magma from the upper conduit into the shallow reservoir . However, since 1959, the chemical composition of the leucite and melilite-bearing nephelinite lavas has not significantly changed, which implies a magma supply from the same magma batch. Nyamuragira was characterised by a shield building phase of activity until a caldera collapse, ca. 300 to 500 years ago. The post-caldera phase has involved effusive activity in the caldera and at numerous flank fissures. The plumbing system consists of an upper reservoir roughly at the basement-volcano interface and averaging a volume of 400 × 10 6 m 3 , a shallow upper-crust stratified reservoir, and a middle-crust mafic magma chamber. Volcanic activity has involved a succession of filling and emptying events at the upper reservoir. Lava volumes of historic eruptions reveal annual output rates averaging 14 × 10 6 m 3 between 1901 and 1976, and 40 × 10 6 m 3 between 1976 and 2012. A drastic increase in activity occurred in December 1976. This event coincided with the January 1977 flank eruption of Nyiragongo and resulted from a main tectonic event in the rift basement that improved the efficiency of magma ascent at both volcanoes. The historic lava composition can be related to six cycles of magma accumulation in, and withdrawal of, the upper reservoir from the shallow stratified reservoir. Similar magma storage and transport systems are known in many effusive systems: the Nyiragongo lava lake shares behavioural characteristics similar to those observed at Kilauea, Erebus, and Erta’Ale. At Nyiragongo and Nyamuragira, magma supply and persistent activity with sudden changes of the magma output rates in relation to tectonic events are also comparable with those of Kilauea, Piton de la Fournaise of Réunion island, and Mount Etna.

中文翻译：

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Nyiragongo 和 Nyamuragira：对东非裂谷系统西部分支基伍裂谷火山活动的回顾

尼拉贡戈火山和尼亚穆拉吉拉火山是维龙加地区东非裂谷西支的两座活火山。它们建于基伍裂谷轴ca。12,000 年前，位于被 Kameronze 断层隔开的两个构造台阶之上。两座火山都显示出自 19 世纪末以来已被观察和记录的一系列火山口内和侧翼喷发。在此，我们对这些出版物和报告进行了整理和审查。尼拉贡戈以其半永久性活跃的熔岩湖而闻名，在撰写本文时（2020 年），该湖是世界上最大的。在几个世纪前因火山口坍塌而结束的主要层状火山的建造过程中，熔岩成分从黄长石变为白榴石，然后变为含黄长石的霞石。历史上活跃的熔岩湖被认为是直接从上部火山内水库、位于火山下方几公里处花岗岩基底的浅水库和更深的地壳内岩浆房中注入的。历史活动自 1894 年以来就有记载，根据熔岩充填和排干之间的突然变化，熔岩湖活动上升和溢出循环，然后下沉和完全或部分排水，可分为八个阶段。在近代历史上（1977 年和 2002 年）两次，主要的侧翼喷发伴随着熔岩湖和上部管道系统的完全排水。自 1948 年以来充满火山口的熔岩，然后在 1977 年和 2002 年的排水事件之后再次被计算为累积体积约为 324 × 10 6 m 3 。相比下，1977 年和 2002 年的侧翼喷发涉及 47 × 10 6 m 3 的熔岩。因此，与火山口填充相关的平均年产量估计在 4 到 13 × 10 6 m 3 之间。熔岩湖的行为从平衡状态发生变化，气体活塞运动和飞溅状态通过间歇性活动的不平衡状态交替变化，直至熔岩湖完全消失。这些变化可能与致密脱气岩浆从上部管道下降到浅层储层的条件有关。然而，自 1959 年以来，白榴石和含黄长石的霞石熔岩的化学成分没有显着变化，这意味着岩浆供应来自同一批次的岩浆。Nyamuragira 的特点是活动的盾构建造阶段，直到火山口坍塌，大约。300 到 500 年前。火山口后阶段涉及火山口和许多侧翼裂缝的渗出活动。管道系统包括一个大致位于基底-火山界面且平均体积为 400 × 10 6 m 3 的上部储层、一个浅层上地壳层状储层和一个中地壳基性岩浆房。火山活动涉及到上层水库的一系列充填和排空事件。历史喷发的熔岩体积显示 1901 年至 1976 年间的年产量平均为 14 × 10 6 m 3 ，1976 年至 2012 年间为 40 × 10 6 m 3。1976 年 12 月活动急剧增加。这一事件与 1977 年 1 Nyiragongo 的侧翼喷发，由裂谷基底中的一次主要构造事件引起，该事件提高了两座火山的岩浆上升效率。历史熔岩成分可能与上层储层中岩浆在浅层层状储层中的六个循环积累和退出有关。类似的岩浆储存和运输系统在许多喷流系统中为人所知：尼拉贡戈熔岩湖的行为特征与在基拉韦厄、埃里伯斯和厄塔阿雷观察到的行为特征相似。在 Nyiragongo 和 Nyamuragira，岩浆供应和持续活动以及与构造事件相关的岩浆输出率突然变化也与基拉韦厄、留尼汪岛的 Piton de la Fournaise 和埃特纳火山相当。Nyiragongo 熔岩湖的行为特征与在 Kilauea、Erebus 和 Erta'Ale 观察到的行为特征相似。在 Nyiragongo 和 Nyamuragira，岩浆供应和持续活动以及与构造事件相关的岩浆输出率突然变化也与基拉韦厄、留尼汪岛的 Piton de la Fournaise 和埃特纳火山相当。Nyiragongo 熔岩湖的行为特征与在 Kilauea、Erebus 和 Erta'Ale 观察到的行为特征相似。在 Nyiragongo 和 Nyamuragira，岩浆供应和持续活动以及与构造事件相关的岩浆输出率突然变化也与基拉韦厄、留尼汪岛的 Piton de la Fournaise 和埃特纳火山相当。