Volcanic Risk Perception and Coping Strategies from Mounts Cameroon and Nyiragongo Eruptions, Central Africa: A Comparative Analysis

Approximately 2,000,000 people are exposed to volcanic risks in communities situated at the flanks of Mounts Cameroon (MC) and Nyiragongo (MN) volcanoes in Central Africa. This study therefore sought to investigate risk perception from four previous eruptions of MC, namely the 1959, 1982, 1999, and 2000 eruptions;and two previous eruptions of MN: 1977 and 2002. The study was initiated with co-design workshops held with major stakeholders in the cities of Buea and Goma at the flanks of MC and MN, respectively, in 2017, to develop the research objectives for the study. A non-random questionnaire survey was later conducted within 14 and 15 communities in Buea and Goma respectively, on the effects, perceived risks, and coping strategies for the chosen eruptions. Three age groups (18 - 30, 31 - 45 and >45 years) and gender (male and female) were considered. The population at the flanks of both volcanoes cited scientific and indigenous factors to be responsible for eruptions from these volcanoes. At MC and MN, ≥45% of the sampled participants (with a higher female population) perceived that the sampled eruptions posed a very high risk to the population. In terms of the effects, the age group of 18 - 30 was the least knowledgeable. In terms of direct effect on persons, over 90% of participants at MC and MN attested that they were overcome by fear/panic. On measures to cope with any likely eruption, the following order was established at the flanks of both volcanoes: sensitization of population, use of religious (prayers) and of traditional/indigenous strategies. In terms of future coping strategies, while the males at MC maintained sensitization as the favourite option, 62% of the males at MN opted for traditional/indigenous strategies. The female population at both MC and MN showed a higher preference for religious strategies like prayers.

Magmatic Evolution of the Western Branch of the East African Rift System Melts: Evidence by Silicate Melt Inclusions, Rock Petrography and Geochemistry of the Nyiragongo 1977 and 2002 Lavas in DRC

Nyiragongo volcanic eruptions of 1977 and 2002 emitted silica-undersaturated lavas named melilite-nephelinites with microlithic to sub-porphyritic textures, and consisted of olivine, clinopyroxene (augite), phlogopite, melilite, magnetite, and rare plagioclases. This melilite-nephelinite as an evolved rock, shows low SiO2 (38.40 - 39.52 wt%) and MgO (3.10 - 4.01 wt%), and relatively high FeOt (13.76 - 14.10 wt%), Al2O3 (15.01 - 16.48 wt%), CaO (11.00 - 12.29 wt%) and Na2O + K2O (10.34 - 11.85 wt%). Unlike LA-ICP-MS on silicate melt inclusions (SMIs) hosted in augite show a pristine melt of picrobasaltic (low Ti-picrite) rock poor in SiO2 (31.14 - 32.26 wt%), FeOt (2.19 - 2.79 wt%), Al2O3 (8.01 - 9.57 wt%), and Na2O + K2O (2.34 - 3.05 wt%), while enriched in MgO (20.27 - 28.63 wt%), and CaO (24.95 - 33.17 wt%). The sums (∑REEs) for lavas and SMIs are ranging 712 - 799 and 43 - 119 ppm respectively. REE contracted multi-element patterns showed a W-feature for most lavas except for SMIs. High Rb/Sr, and low Ba/Rb, Zr/Nb, and Sm/Hf ratios of lavas suggest a phlogopite-rich source of materials. .

Influence of the Partial Substitution of Industrial Clinker by Volcanic Lava Powder from Nyiragongo Volcano on the Physical Properties of Mortars

This study evaluates the pozzolanicity of Nyiragongo volcano lava flows in Congo by an indirect method using mortars with different rock powder proportions. The clinker used is a locally produced alite clinker, whose chemical and mineralogical composition was determined by XRF, Bogue and Taylor formulas. The lava flows were collected from the 2002, 2010 and 2021 eruption sites, and were characterized by XRF, CIPW normative mineralogy and geomechanical tests. The results show that Nyiragongo rocks are ultrabasic, silica- and alkali-rich, and contain minerals like nepheline, wollastonite and leucite. They satisfy the natural pozzolan criterion, and have pozzolanic activity indices above 70%. These rocks also have high RC and LA resistances, ranging from 190 MPa to 45 MPa, and from 18% to 32.6%, respectively. The rock powder addition in the mortars reduces mechanical resistances and increases setting times, except for a 5% replacement rate, which speeds up hardening. Nyiragongo lava can be used as a pozzolanic addition to produce a CEM II/B-P 32.5 cement.

Pure forsterite in Nyiragongo lavas: evidence for subsolidus oxidation of volcanic rocks

Some volcanic rocks from Nyiragongo volcano in the Democratic Republic of Congo contain highly oxidized olivine crystals.These olivines crystals are made of two phases,dark olivine on backscattered electron images of pure forsterite composition and grey Mg-poor areas made of olivine and iron-rich oxides.Calculation of the initial composition confirms that they are primary olivine with late separation of two different olivine compositions.Pure forsterite is enriched in SiO_(2) but contains lower amounts of CaO than Fe-rich areas,in agreement with expected partitioning of these elements related to the composition of the olivine.Iron-rich oxides formed around or inside the olivine crystals during the separation process and confirm a highly oxidized environment during their evolution.We propose that this separation occurred during subsolidus recrystallization under high fO_(2) conditions of the olivine crystals after cooling of the volcanic rocks.It provides evidences for circulation of iron-rich fluids or gas inducing deuteritic processes occurring in the large volcanic cone of the Nyiragongo,in relation with the presence of a shallow magma chamber connected to a large and permanent lava lake.

Towards a Volumetric Variation of Lake Kivu Gases by the Nyamulagira and Nyiragongo Volcanoes

After the volcanic eruption of January 17th, 2002, Goma Volcano Observatory (OVG) initiated carbon dioxide (CO2) monitoring in the fractures south of the Nyiragongo volcano and at the northern edge of Lake Kivu. During the period from March 17th, 2017 to June 10th, 2020, twice a week, a GA 5000 gasometer was used for CO2 in the fractures as well as in the mazukus, respectively, as part of a project funded by the Kingdom of the Netherlands through the Lake Kivu Monitoring Program (LKMP) in Rwanda. The level of volcanic activity was determined by the volume of gas emitted by the volcano and measured by a DOAS and the seismicity measured by a network of 15 seismometers managed by the OVG. The results show that the concentration of CO2 in the active fractures from recent Nyiragongo eruptions varies with volcanic activity and the occurrence of a large earthquake in the East African Rift;but in the mazukus there is almost no relationship between CO2 content and volcanic activity. The study also shows that the influence of carbon dioxide in mazukus on the carbon dioxide into the Lake Kivu waters remains a major research question. The purpose of this study is to establish the relationship between the existing Carbon Dioxide (mazukus) in the Northern watershed and that of the deep waters of Lake Kivu.