G-force measurements at Mount Nyiragongo

To evaluate the mechanical stress on the volcanic edifice that results from lava lake level variations, we deployed a self-recording, differential capacitance (MEMS Inertial Sensor STMicroelectronics LIS3LV02DQ), 3-axis X6-1A accelerometer (Gulf Coast Data Concepts, LLC) at a distance of ~100m from the center of the Nyiragongo lava lake on freshly erupted lava flows. The device range was used in high (12-bit) resolution mode, which corresponds to a sensitivity of about 1 mg. The device was set to high-sensitivity mode with four additional bits to improve resolution, yet with a much lower signal-noise ratio. Once in position, the accelerometer continuously recorded data for three-day periods in June 2010. The system was oriented so that the X- and Y-axes form a plain parallel to the lava lake. During data collection, we did not attempt to calibrate the precision of the angle because relative G-force measurements were required instead of absolute G-force measurements. To distinguish the tiny accelerations caused by temperature differentials of the atmosphere, from the forces caused by magma movements, the temperature of the X6-1A device was continuously recorded. Temperature variations were corrected for by applying a de-correlation method to the recorded signal. Data was collected at 20 Hz, regrouped into batches that cover 1 hour per observation and associated with one averaged temperature measurement. This method was reproducible because diurnal temperature variations were the main cause for heating and cooling

Mineralogy, geochemistry and petrogenesis of Nyiragongo and Nyamuragira volcanic rocks (Virunga Province D.R. Congo)

The Virunga Volcanic Province (VVP) lies close to the northern end of the western branch of the East African Rift System (EARS). Volcanism started about 11 Ma ago and continuing to the present. The two active volcanoes of VVP, Nyamuragira and Nyiragongo are located along the seismically active sector of the western rift. Nyamuragira (3058 a.s.l.) is a large volcanic shield characterized by alkaline rocks ranging from basanite to tephrite and rare transitional basalt. Nyiragongo is a stratovolcano (3469 a.s.l.) characterized by rock types such as melilitite, melilite nephelinite, pyroxene nephelinite, leucite nephelinite, leucitite and leucite tephrite. Samples include parasitic cones and lava fields of the volcanic complexes from 1938 products until now, and products of 2002 eruption sampled from the proximal vent area to the distal outcrops. Nyamuragira basanites and tephrites are porphyritic with phenocrysts of olivine and clinopyroxene. Basanites have MgO (12.05-13.60 wt.%), Cr (790-926 ppm) and Ni (245-309 ppm) contents within the ranges expected for mantle-derived liquids. The transitional basalts have higher MgO (> 15 wt.%), Cr (> 969 ppm) and Ni (> 750 ppm) than basanites. Such enrichment in these elements is due to excess of olivine phenocrysts. Nyamuragira basanites have Zr/Nb (3.9-4.0), Ba/Nb (11-12) and La/Nb (0.86-0.9) ratios typical of mantle or OIB values. The primitive mantlenormalized incompatible element patterns of Nyamuragira show peaks at Ba and Nb and smoothly decreasing normalizedabundances from Nb to Lu. The high Lan/Ybn ratio (18) indicates that the Nyamuragira basanites are low degree partial melts of a slightly incompatible element-enriched mantle source in the garnet stability field. The least differentiated mafic rocks of Nyiragongo are melilite nephelinites and olivine melilitites. Melilite has akermanite composition, olivine ranges from forsterite-fayalite to kirschsteinite and clinopyroxene is diopside. All samples are feldspar-free. The composition of the glass is often rich in Ba content (up to 5 wt.% BaO). These rocks have higher CaO (~16.3 wt.%) and lower SiO2 (~ 40 wt.%), MgO (8.7-9.1 wt.%) and compatible elements concentrations (Cr = 380-395 ppm; Ni = 155-169 ppm) than Nyamuragira basanites. Their incompatible element patterns are also more enriched than those of Nyamuragira basanites with high LREE/HREE (Lan/Ybn = 42). The low Zr/Nb (2.1) of the olivine melilitites indicate that the Nyiragongo olivine melilitites are melt products of an incompatible element-enriched source. In addition, their low heavy REE contents suggest that they were generated within the garnet-peridotite stability field within the lithospheric mantle. The compositional variation within the Nyiragongo volcanic rocks was largely controlled by low pressure fractional crystallization of the observed phases

Gas emission measurements of the active lava lake of Nyiragongo, DR Congo

In June 2007 and July 2010 spectroscopic measurements and chemical in-situ studies were carried out at Nyiragongovolcano located 15 km north of the city Goma, North Kivu region (DRC), both at the crater rim and within the crater itself, next to the lava lake. Nyiragongo volcano belongs to the Virunga volcanic chain and it is associated with the Western branch of the Great Rift Valley. The volcanism at Nyiragongo is caused by the rifting of the Earth’s crust where two parts of the African plates are breaking apart. Niyragongo crater contains the biggest lava lake on Earth and it is considered one of the most active volcanoes in the world.The ground-based remote sensing technique MAX-DOAS (Multi-Axis Differential Optical Absorption Spectroscopy)using scattered sunlight has been applied during both field trips at the crater rim of the volcano tomeasure sulphur dioxide, halogen oxides and nitrogen oxide. Additionally filter pack and spectroscopic in-situ carbon dioxide measurements were carried out, as well as SO2 flux measurements by a scanning DOAS instrumentfrom the NOVAC project at the flank of the volcano.Nyiragongo is the first rift volcano where halogen oxides have been observed in the plume.Observations indicate that the gas composition of Nyiragongo might change with a changing lava lake level inshort and long-term time scales. Before and during an overflow of the lava lake the molar ratios of BrO/SO2 weredecreasing in 2007 and 2010 from about 3.10-5 to about 0 (below the detection limit). Such a decreasing trendwas also observed before and during the eruption of Mt. Etna 2006 and 2008.In a larger timescale between 2007 and 2010 the molar ratios of S/Cl and CO2/SO2 generally decreased from 6.7 -16.5 to 0.7 – 2.1, from 5 -10 to 1 - 5, respectively. The lower S/Cl and CO2/SO2 could lead to the conclusion thatthe magma reservoir below Niyragongo has had no new input from a deeper source.The chemical composition as well as its temporal variability within the volcanic plume from the lava lake will be discussed, as well as its implication on the understanding of the dynamics of the plumbing system of this volcano

Gas emission measurements of the active lava lake of Nyiragongo, DR Congo

In June 2007 and July 2010 spectroscopic measurements and chemical in-situ studies were carried out at Nyiragongo volcano located 15 km north of the city Goma, North Kivu region (DRC), both at the crater rim and within the crater itself, next to the lava lake. Nyiragongo volcano belongs to the Virunga volcanic chain and it is associated with the Western branch of the Great Rift Valley. The volcanism at Nyiragongo is caused by the rifting of the Earth’s crust where two parts of the African plates are breaking apart. Niyragongo crater contains the biggest lava lake on Earth and it is considered one of the most active volcanoes in the world. The ground-based remote sensing technique MAX-DOAS (Multi-Axis Differential Optical Absorption Spectroscopy) using scattered sunlight has been applied during both field trips at the crater rim of the volcano to measure sulphur dioxide, halogen oxides and nitrogen oxide. Additionally filter pack and spectroscopic in-situ carbon dioxide measurements were carried out, as well as SO2 flux measurements by a scanning DOAS instrument from the NOVAC project at the flank of the volcano. Nyiragongo is the first rift volcano where halogen oxides have been observed in the plume. Observations indicate that the gas composition of Nyiragongo might change with a changing lava lake level in short and long-term time scales. Before and during an overflow of the lava lake the molar ratios of BrO/SO2 were decreasing in 2007 and 2010 from about 3.10-5 to about 0 (below the detection limit). Such a decreasing trend was also observed before and during the eruption of Mt. Etna 2006 and 2008. In a larger timescale between 2007 and 2010 the molar ratios of S/Cl and CO2/SO2 generally decreased from 6.7 - 16.5 to 0.7 – 2.1, from 5 -10 to 1 - 5, respectively. The lower S/Cl and CO2/SO2 could lead to the conclusion that the magma reservoir below Niyragongo has had no new input from a deeper source. The chemical composition as well as its temporal variability within the volcanic plume from the lava lake will be discussed, as well as its implication on the understanding of the dynamics of the plumbing system of this volcano

Birth of a lava lake: Nyamulagira volcano 2011-2015

Since 1938, Nyamulagira volcano (Democratic Republic of Congo) has operated as a classic pressurized basaltic closed system, characterized by frequent dike-fed flank eruptions. However, on June 24, 2014, an active lava lake was observed in its summit, after a period of 76 years. The small lava lake is now exposed at the bottom of a pit-crater and is rising and growing. Based on satellite-derived infrared (IR) data, SO2 fluxes and periodic field surveys, we provide evidence that the development of the lava lake was gradual and occurred more than 2 years before it was first observed in the field. Notably, this process followed the voluminous 2011-2012 distal flank eruption and was coeval with weakening of the central rock column below the summit. Hence, the opening and development of the pit-crater favoured the continuous rise of fresh magma through the central conduit and promoted the gradual "re-birth" of the Nyamulagira lava lake. Budgeted volumes of magma erupted, and magma degassed at depth indicate that the formation of the lava lake is due to the draining and refilling of a shallow plumbing system (1-2 km depth), probably in response to the rift-parallel 2011-2012 distal eruption. We thus suggest that the transition from lateral to central activity did not result from a substantial change in the magma supply rate but, more likely, from the perturbation of the plumbing system (and related stress field) associated with the distal eruption. The processes observed at Nyamulagira are not unique and suggest that rift-fissure eruptions, in addition to triggering caldera collapses or lava lake drainages, may also induce a progressive resumption of central vent activity. Current activity at Nyamulagira represents a tangible and major hazard for the population living at the base of its southern flank

Impact of volcanic plume emissions on rain water chemistry during the January 2010 Nyamuragira eruptive event: Implications for essential potable water resources

On January 2, 2010 the Nyamuragira volcano erupted lava fountains extending up to 300m vertically along an ∼1.5km segment of its southern flank cascading ash and gas on nearby villages and cities along the western side of the rift valley. Because rain water is the only available potable water resource within this region, volcanic impacts on drinking water constitutes a major potential hazard to public health within the region. During the 2010 eruption, concerns were expressed by local inhabitants about water quality and feelings of physical discomfort (e.g. nausea, bloating, indigestion, etc.) after consuming rain water collected after the eruption began. We present the elemental and ionic chemistry of drinking water samples collected within the region on the third day of the eruption (January 5, 2010). We identify a significant impact on water quality associated with the eruption including lower pH (i.e. acidification) and increases in acidic halogens (e.g. F- and Cl-), major ions (e.g. SO42-, NH4+, Na+, Ca2+), potentially toxic metals (e.g. Al3+, Mn2+, Cd2+, Pb2+, Hf4+), and particulate load. In many cases, the water's composition significantly exceeds World Health Organization (WHO) drinking water standards. The degree of pollution depends upon: (1) ash plume direction and (2) ash plume density. The potential negative health impacts are a function of the water's pH, which regulates the elements and their chemical form that are released into drinking water. © 2012 Elsevier B.V