Mazuku

{{short description|Pocket of carbon dioxide–rich air that can be lethal}} [[File:Mazuku 1.png|thumb|Mazuku forming in a low morphological depression on the foothills of Mt. Amiata, Italy, where CO₂-rich fog accumulates in a ditch]] '''Mazuku''' ([[Swahili language|Swahili]] for "evil winds") are pockets of dry, cold [[carbon dioxide]]-rich gases released from vents or fissures in volcanically and tectonically active areas, mixed with dispersed atmospheric air and accumulating in typically low-lying areas.<ref name=":011">{{Cite journal|last1=Smets|first1=Benoît|last2=Tedesco|first2=Dario|last3=Kervyn|first3=François|last4=Kies|first4=Antoine|last5=Vaselli|first5=Orlando|last6=Yalire|first6=Mathieu Mapendano|date=2010-12-01|title=Dry gas vents ("mazuku") in Goma region (North-Kivu, Democratic Republic of Congo): Formation and risk assessment|url=https://linkinghub.elsevier.com/retrieve/pii/S1464343X10000828|journal=Journal of African Earth Sciences|series=Active Volcanism and Continental Rifting in Africa|volume=58|issue=5|pages=787–798|bibcode=2010JAfES..58..787S|doi=10.1016/j.jafrearsci.2010.04.008|issn=1464-343X|url-access=subscription}}</ref><ref name=":57">{{Cite journal|last1=Kagabo|first1=Laurent Bizimungu|last2=Balagizi|first2=Charles M.|last3=Yalire|first3=Mathieu M.|last4=Habamungu|first4=Richard B.|last5=N.|first5=Samuel Kasigwa|last6=Rusimbuka|first6=Marcel B.|last7=Seza|first7=Diane B.|last8=Bonheur|first8=Rugain Ngangu|date=2024-04-11|title=War Displaced Persons Facing the Risks Associated with Mazuku In and Around the Goma City|url=https://ijrpr.com/uploads/V5ISSUE4/IJRPR25697.pdf|journal=International Journal of Research Publication and Reviews|volume=5|issue=4|pages=7321–7327|doi=10.55248/gengpi.5.0424.10111}}</ref><ref name=":111">{{Cite journal|last1=Tedesco|first1=D.|last2=Tassi|first2=F.|last3=Vaselli|first3=O.|last4=Poreda|first4=R. J.|last5=Darrah|first5=T.|last6=Cuoco|first6=E.|last7=Yalire|first7=M. M.|date=January 2010|title=Gas isotopic signatures (He, C, and Ar) in the Lake Kivu region (western branch of the East African rift system): Geodynamic and volcanological implications|url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2008JB006227|journal=Journal of Geophysical Research: Solid Earth|language=en|volume=115|issue=B1|bibcode=2010JGRB..115.1205T|doi=10.1029/2008JB006227|issn=0148-0227}}</ref> Since carbon dioxide (CO₂) is ~1.5<ref name=":2213">{{Cite journal|last1=Balagizi|first1=Charles M.|last2=Kies|first2=Antoine|last3=Kasereka|first3=Marcellin M.|last4=Tedesco|first4=Dario|last5=Yalire|first5=Mathieu M.|last6=McCausland|first6=Wendy A.|date=2018-08-01|title=Natural hazards in Goma and the surrounding villages, East African Rift System|url=https://link.springer.com/article/10.1007/s11069-018-3288-x|journal=Natural Hazards|language=en|volume=93|issue=1|pages=31–66|bibcode=2018NatHa..93...31B|doi=10.1007/s11069-018-3288-x|issn=1573-0840|url-access=subscription}}</ref> times heavier than [[Atmosphere of Earth|air]], it tends to flow downhill, hugging the ground like a low [[fog]] and gathering in enclosed spaces with poor ventilation—such as [[lava tube]]s, ditches, depressions, caves, and house basements—or in the stratified water layers of [[meromictic lakes]] if a [[water column]] exists.<ref name=":137">{{Cite journal|last1=Hirslund|first1=F.|last2=Morkel|first2=P.|date=2020-01-01|title=Managing the dangers in Lake Kivu – How and why|url=https://linkinghub.elsevier.com/retrieve/pii/S1464343X19303279|journal=Journal of African Earth Sciences|volume=161|article-number=103672|bibcode=2020JAfES.16103672H|doi=10.1016/j.jafrearsci.2019.103672|issn=1464-343X|url-access=subscription}}</ref><ref>{{Cite journal|last=Zana Lambadi|first=Aimé|date=2023|title=Les impacts environnementaux des éruptions volcaniques dans une zone à faible taux d'exploitation technologique: cas de la province du Nord-Kivu en RD Congo|url=https://csnrdc.net/wp-content/uploads/journal/published_paper/volume-2/issue-1/HT3uFOYQ.pdf|journal=Revista Congolaise des Sciences et Technologies|volume=02|issue=1|pages=280–288 (2023)|doi=10.59228/rcst.023.v2.i1.30|via=Article de recherche}}</ref><ref name=":247">{{Cite journal|last1=Viveiros|first1=Fátima|last2=Silva|first2=Catarina|date=October 2024|title=Hazardous volcanic CO2 diffuse degassing areas – A systematic review on environmental impacts, health, and mitigation strategies|journal=iScience|volume=27|issue=10|article-number=110990|doi=10.1016/j.isci.2024.110990|issn=2589-0042|pmc=11490718|pmid=39429787|bibcode=2024iSci...27k0990V}}</ref> In high concentrations (≥&nbsp;1% by volume), they can pose a deadly risk to both humans and animals in the surrounding area because they are undetectable by [[olfactory]] or visual senses in most conditions.<ref name=":011"/><ref name=":111"/>

Mazuku primarily occur on the northern shores of [[Lake Kivu]] to either side of the twin towns of [[Goma]] ([[Democratic Republic of the Congo]]) and [[Gisenyi]] ([[Rwanda]]), where local communities use this term in their vernacular (Kinyabwisha language) to describe the dangerous gases.<ref name=":2213"/> They believe mazuku occur in cursed locations where invisible forces roam, silently killing people in the night while they sleep.<ref name=":611">{{Cite report|title=Open-File Report|last1=Tuttle|first1=M. L.|last2=Lockwood|first2=John P.|date=1990|publisher=U.S. Geological Survey|issue=90–691|doi=10.3133/ofr90691|language=en|last3=Evans|first3=William C.|chapter-url=https://pubs.usgs.gov/publication/ofr90691|chapter=Natural hazards associated with Lake Kivu and adjoining areas of the Birunga volcanic field, Rwanda and Zaire, Central Africa; final report}}</ref><ref name=":215">{{Cite journal|last1=Le Guern|first1=F.|last2=Tazieff|first2=H.|last3=Pierret|first3=R. Faivre|date=1982-06-01|title=An example of health hazard: People killed by gas during a phreatic eruption: Diëng plateau (Java, Indonesia), February 20th 1979|url=https://link.springer.com/article/10.1007/BF02600430|journal=Bulletin Volcanologique|language=en|volume=45|issue=2|pages=153–156|bibcode=1982BVol...45..153L|doi=10.1007/BF02600430|issn=1432-0819|url-access=subscription}}</ref> In many places where mazuku occur, CO₂ levels fall during daytime but can rise to significantly dangerous concentration levels of about 90% at night, early mornings, or evening hours, posing a great threat.<ref name=":2213"/><ref name=":611"/> This is because at night the atmospheric temperature drops and wind speeds significantly reduce.<ref name=":611"/><ref name=":304">{{Cite journal|last1=van Gardingen|first1=Paul R.|last2=Grace|first2=John|last3=Harkness|first3=Douglas D.|last4=Miglietta|first4=Franco|last5=Raschi|first5=Antonio|date=1995-02-01|title=Carbon dioxide emissions at an Italian mineral spring: measurements of average CO2 concentration and air temperature|url=https://linkinghub.elsevier.com/retrieve/pii/016819239402176K|journal=Agricultural and Forest Meteorology|volume=73|issue=1|pages=17–27|doi=10.1016/0168-1923(94)02176-K|issn=0168-1923|url-access=subscription}}</ref> These conditions slow the dispersal of these heavy gases into the atmosphere, allowing them to accumulate in lower-lying areas, such as valleys and depressions.<ref name=":95">{{Cite journal|last1=Rogie|first1=John D|last2=Kerrick|first2=Derrill M|last3=Sorey|first3=Michael L|last4=Chiodini|first4=Giovanni|last5=Galloway|first5=Devin L|date=June 2001|title=Dynamics of carbon dioxide emission at Mammoth Mountain, California|url=https://linkinghub.elsevier.com/retrieve/pii/S0012821X01003442|journal=Earth and Planetary Science Letters|language=en|volume=188|issue=3–4|pages=535–541|bibcode=2001E&PSL.188..535R|doi=10.1016/S0012-821X(01)00344-2|url-access=subscription}}</ref><ref name=":316">{{Cite journal|last=Vaselli|first=Orlando|date=January 2003|title=The "evil winds" (mazukus) at Nyiragongo volcano (Democratic Republic of Congo)|url=https://www.researchgate.net/publication/232091469|journal=Acta Vulcanologica|volume=14-15}}</ref><ref name=":274">{{Cite journal|last1=Viveiros|first1=Fátima|last2=Gaspar|first2=João L.|last3=Ferreira|first3=Teresa|last4=Silva|first4=Catarina|date=July 2016|title=Hazardous indoor CO2 concentrations in volcanic environments|url=https://linkinghub.elsevier.com/retrieve/pii/S0269749116303529|journal=Environmental Pollution|language=en|volume=214|pages=776–786|bibcode=2016EPoll.214..776V|doi=10.1016/j.envpol.2016.04.086|pmid=27155095|url-access=subscription}}</ref>

== Geological setting and occurrence == [[File:East African Rift System.png|thumb|Map of the East African Rift System (EARS), spanning ~4,000 km and showing the Eastern and Western rift branches. The map highlights areas of tectonic activity, volcanic hazards, and CO₂ gas releases, including mazuku emissions, particularly on the Virunga Volcanic Province (VVP) and the Rungwe Volcanic Province (RVP) (red squares)]]

The [[East African Rift]] System (EARS) is formed by the divergence of three ancient [[craton]]ic plates: the [[Somali Plate|Somalian plate]], the [[Nubian plate]], and the [[Arabian Plate|Arabian plate]], which are splitting apart due to the influence of a [[mantle plume]] beneath them.<ref>{{Cite journal|last1=Chu|first1=Dezhi|last2=Gordon|first2=Richard G.|date=March 1999|title=Evidence for motion between Nubia and Somalia along the Southwest Indian ridge|url=https://www.nature.com/articles/18014|journal=Nature|language=en|volume=398|issue=6722|pages=64–67|bibcode=1999Natur.398...64C|doi=10.1038/18014|issn=1476-4687|url-access=subscription}}</ref> The rift extends ~4,000&nbsp;km, starting from the [[Afar triple junction]] in the northern [[Ethiopian Plateau]] and running southwards.<ref name=":145">{{Cite journal|last=Ring|first=Uwe|date=2014|title=The East African Rift System|url=https://earthjay.com/earthquakes/20180308_malawi/ring_2014_east_africa_rift.pdf|journal=Austrian Journal of Earth Sciences|volume=107|pages=132–146}}</ref> It is divided into two main segments: the volcanically active Eastern branch (~45 [[Million years ago|Ma]]), which passes through Djibouti, Eritrea, Kenya, and northeastern Tanzania; and the younger, seismically active Western branch (~5 and 8 Ma), that cuts through the Democratic Republic of the Congo (DRC), Uganda, Rwanda, Burundi, southwestern Tanzania, Zambia, Malawi, and Zimbabwe and terminates at the [[Okavango Delta]] in [[Botswana]].<ref name=":27">{{Cite journal|last1=Yirgu|first1=G.|last2=Ebinger|first2=C.J.|last3=Maguire|first3=P.K.H.|date=January 2006|title=The Afar volcanic province within the East African Rift System: introduction|url=https://www.lyellcollection.org/doi/10.1144/GSL.SP.2006.259.01.01|journal=Geological Society, London, Special Publications|language=en|volume=259|issue=1|pages=1–6|bibcode=2006GSLSP.259....1Y|doi=10.1144/GSL.SP.2006.259.01.01|issn=0305-8719|url-access=subscription}}</ref> The rifting process is responsible for the tectonic and volcanic activity in [[East Africa]], leading to the formation of deep [[rift lake]] basins, such as [[Lake Tanganyika]], [[Lake Malawi]], [[Lake Rukwa]], [[Lake Albert (Africa)|Lake Albert]], and [[Lake Kivu]], as well as frequent natural disasters such as earthquakes, volcanic eruptions, and massive landslides, along with prolonged dry CO₂-rich gas emissions like mazuku (toxic gas) releases.<ref>{{Cite journal|last1=Ebinger|first1=C.|last2=Djomani|first2=Y. Poudjom|last3=Mbede|first3=E.|last4=Foster|first4=A.|last5=Dawson|first5=J. B.|date=November 1997|title=Rifting Archaean lithosphere: the Eyasi-Manyara-Natron rifts, East Africa|url=https://www.lyellcollection.org/doi/10.1144/gsjgs.154.6.0947|journal=Journal of the Geological Society|language=en|volume=154|issue=6|pages=947–960|bibcode=1997JGSoc.154..947E|doi=10.1144/gsjgs.154.6.0947|issn=0016-7649|url-access=subscription}}</ref><ref>{{Cite journal|last=Ebinger|first=Cynthia|date=1993|title=EVALUATION OF NATURAL HAZARDS IN THE NORTHERN PART OF THE MALAWI RIFT (TANZANIA)|url=https://www.academia.edu/48451194|journal=Mus. Roy. Afr. Centr., Tervuren (Belg.), Dept. Geol, Min.|volume=Rapp, ann. 1991-1992|pages=83–86}}</ref><ref name=":011"/>

It has been observed that most mazukus are found along the Western branch of the EARS, particularly in areas of active volcanic and tectonic activity. These areas include:

* [[Virunga Mountains|Virunga Volcanic Province]] (VVP) at the foothills of the volcanic mountains of [[Nyamuragira|Nyamulagira]] and [[Mount Nyiragongo|Nyiragongo]], north of Lake Kivu, and particularly in the busy city centers of [[Goma]] and Sake ([[DRC]]) and [[Gisenyi]] ([[Rwanda]]).<ref name=":316"/> * [[Rungwe Volcanic Province]] (RVP) in southwestern [[Tanzania]], at the [[triple junction]] of the Tanganyika–Malawi–Usangu rifts,<ref name=":27"/><ref name=":0">{{Cite journal|last1=Kimani|first1=C. N.|last2=Kasanzu|first2=C. H.|last3=Tyne|first3=R. L.|last4=Mtili|first4=K. M.|last5=Byrne|first5=D. J.|last6=Kazimoto|first6=E. O.|last7=Hillegonds|first7=D. J.|last8=Ballentine|first8=C. J.|last9=Barry|first9=P. H.|date=2021-12-30|title=He, Ne, Ar and CO2 systematics of the Rungwe Volcanic Province, Tanzania: Implications for fluid source and dynamics|url=https://linkinghub.elsevier.com/retrieve/pii/S0009254121005271|journal=Chemical Geology|volume=586|article-number=120584|doi=10.1016/j.chemgeo.2021.120584|bibcode=2021ChGeo.58620584K|issn=0009-2541|url-access=subscription}}</ref> where CO₂ is mined commercially by [[TOL Company Limited]] for supply to the [[beverage industry]].<ref name=":4">{{Cite journal|last1=Barry|first1=P. H.|last2=Hilton|first2=D. R.|last3=Fischer|first3=T. P.|last4=de Moor|first4=J. M.|last5=Mangasini|first5=F.|last6=Ramirez|first6=C.|date=2013-02-15|title=Helium and carbon isotope systematics of cold "mazuku" CO2 vents and hydrothermal gases and fluids from Rungwe Volcanic Province, southern Tanzania|url=https://linkinghub.elsevier.com/retrieve/pii/S0009254112003099|journal=Chemical Geology|series=Frontiers in Gas Geochemistry|volume=339|pages=141–156|bibcode=2013ChGeo.339..141B|doi=10.1016/j.chemgeo.2012.07.003|issn=0009-2541|url-access=subscription}}</ref>

== Formation == Geologically, mazuku are natural CO₂ emissions linked to magmatically and tectonically active regions, such as young and active or dormant volcanic systems, active hydrothermal systems, and deep fault structures systems.<ref name=":011"/><ref name=":252"/><ref name=":611"/> Isotopic signatures from helium and CO₂ gas analyses confirm that the origin of mazuku is mainly [[Magma|magmatic]], as opposed to thermal decomposition of organic matter.<ref name=":57"/><ref name=":111"/><ref name=":316"/><ref>{{Cite journal|last=Kerrick|first=Derrill M.|date=November 2001|title=Present and past nonanthropogenic CO 2 degassing from the solid earth|url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2001RG000105|journal=Reviews of Geophysics|language=en|volume=39|issue=4|pages=565–585|doi=10.1029/2001RG000105|issn=8755-1209}}</ref> These gases are temporarily trapped and stored in subsurface pockets, such as [[lava tubes]] formed during previous eruptions, and remain isolated from the rest of the surrounding hydrothermal system.<ref name=":0"/><ref name=":4"/> Over time, they are released following porous pathways and channeled to the surface through a network of extensional fissures, faults, or fractures.<ref name=":011"/><ref name=":111"/> Once at the surface, they accumulate in cavities or in low-lying areas (depressions) due to their densities and the influence of gravity.<ref name=":011"/> In [[meromictic lake]]s such as [[Lake Kivu]], [[Lake Nyos]], and [[Lake Monoun]], the CO₂-rich gases remain trapped in the dense, cold, and anoxic stratified lower layers ([[monimolimnion]]), which do not mix with the O₂-rich surface layers ([[mixolimnion]]) due to density discrepancies.<ref name=":611"/><ref name=":011"/>

In [[anoxic zones]], methanogenic bacteria convert carbon dioxide (CO₂) into methane ({{CH4}}) through a process called [[methanogenesis]], whereby over time, both CO₂ and CH₄ accumulate under extremely high pressure, creating a potential future [[limnic eruption]] disaster.<ref name=":611"/><ref name=":1">{{Cite journal|last1=Kling|first1=George W.|last2=Clark|first2=Michael A.|last3=Wagner|first3=Glen N.|last4=Compton|first4=Harry R.|last5=Humphrey|first5=Alan M.|last6=Devine|first6=Joseph D.|last7=Evans|first7=William C.|last8=Lockwood|first8=John P.|last9=Tuttle|first9=Michele L.|last10=Koenigsberg|first10=Edward J.|date=1987-04-10|title=The 1986 Lake Nyos Gas Disaster in Cameroon, West Africa|url=https://www.science.org/doi/10.1126/science.236.4798.169|journal=Science|language=en|volume=236|issue=4798|pages=169–175|doi=10.1126/science.236.4798.169|pmid=17789781|bibcode=1987Sci...236..169K|issn=0036-8075|url-access=subscription}}</ref><ref>{{Cite journal|last1=Votava|first1=Jillian E.|last2=Johnson|first2=Thomas C.|last3=Hecky|first3=Robert E.|date=2017-01-10|title=Holocene carbonate record of Lake Kivu reflects the history of hydrothermal activity|journal=Proceedings of the National Academy of Sciences|language=en|volume=114|issue=2|pages=251–256|doi=10.1073/pnas.1609112113|doi-access=free|issn=0027-8424|pmc=5240696|pmid=28028207|bibcode=2017PNAS..114..251V}}</ref> However, CH₄ is currently extracted economically in Lake Kivu through degassing, which reduces the risk of a dangerous limnic eruption while providing an energy source for power generation.<ref name=":137"/><ref name=":611"/> Mazuku can extend up to 100m in length and cover an area of up to 4,700m², as seen in the mazuku of [[Bulengo Seminaire]] on the shores of Lake Kivu, DRC. It has been observed that there is a strong correlation between the occurrence and location of mazuku with the regional alignment of tectonic faults and fracture network.<ref name=":011"/><ref name=":2213"/>

== Geochemical composition and origin == The geochemical composition of mazuku gases consists mainly of CO₂ and a variable mixture of other [[Atmosphere|atmospheric]] components, such as N₂, O₂, and [[argon]] (Ar), with smaller amounts of methane (CH₄), [[hydrogen sulfide]] (H₂S), and water vapour.<ref name=":011"/><ref name=":2213"/> In these gases, CO₂ concentrations range between 12% and 99%, argon concentrations range from 0.01% to 0.85%, and CH₄ concentrations range from 0.0002% to 0.002%.<ref name=":0"/><ref name=":4"/> Helium is also present in low concentrations, ranging between 0.0003% and 0.004%.<ref name=":316"/><ref name=":0"/>

The [[isotopic signature]] of He-Ar and CO₂ systematics identify mazuku sources to be derived from both the [[Mantle plume|mantle]] (magmatic sources) and the crust, with significant potential secondary modification processes such as magma mixing and solubility-driven degassing fractionation.<ref name=":0"/><ref>{{Cite journal|last1=Barry|first1=P. H.|last2=Hilton|first2=D. R.|last3=Füri|first3=E.|last4=Halldórsson|first4=S. A.|last5=Grönvold|first5=K.|date=2014-06-01|title=Carbon isotope and abundance systematics of Icelandic geothermal gases, fluids and subglacial basalts with implications for mantle plume-related CO2 fluxes|url=https://linkinghub.elsevier.com/retrieve/pii/S0016703714001471|journal=Geochimica et Cosmochimica Acta|volume=134|pages=74–99|doi=10.1016/j.gca.2014.02.038|issn=0016-7037}}</ref> The dry gases are continuously released very slowly through a [[passive degassing]] mechanism from the earth's interior via vents, fractures, cracks, hot springs, fumaroles, and gas plumes, without the need or presence of an active volcanic eruption.<ref name=":011"/><ref name=":37">{{Cite journal|last1=Spilliaert|first1=N.|last2=Allard|first2=P.|last3=Métrich|first3=N.|last4=Sobolev|first4=A. V.|date=April 2006|title=Melt inclusion record of the conditions of ascent, degassing, and extrusion of volatile-rich alkali basalt during the powerful 2002 flank eruption of Mount Etna (Italy)|url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2005JB003934|journal=Journal of Geophysical Research: Solid Earth|language=en|volume=111|issue=B4|bibcode=2006JGRB..111.4203S|doi=10.1029/2005JB003934|issn=0148-0227}}</ref>

=== Surface manifestations === [[File:Mazuku at a lava front.png|thumb|Patchy vegetation and bareland areas due to high CO₂ flux in the soil around the lava front near Goma city (particularly affecting the areas surrounding refugee camps)]]Areas with mazuku can be readily identified in the field through several distinctive characteristics and features, such as: * Peculiar types and species of vegetation that thrive in CO₂-rich waters and gases, such as [[cyperus papyrus]], [[fern]], [[Reed (plant)|reeds]], and [[Poaceae|grasses]].<ref name=":2213" /><ref name=":316" /> * Burnt-out vegetation and altered rocks due to high acidity levels associated with normally elevated CO₂ concentrations (70–90v.%), resulting in patches of weathered bareland.<ref name=":011" /><ref name=":57" /><ref name=":316" /> * Regions with ultrahigh CO₂ concentrations, where the high CO₂/O₂ ratio can be perceived as a sensation of heat on human skin, a condition related to [[hypercapnia]].<ref name=":252">{{Cite journal|last=Kasereka|first=Marcellin|date=December 2017|title=ORIGINAL LES RISQUES LIES AUX MAZUKU DANS LA REGION DE GOMA, REPUBLIQUE DEMOCRATIQUE DU CONGO (RIFT EST-AFRICAIN) RISKS ASSOCIATE WITH MAZUKU IN THE GOMA AREA, DEMOCRATIC REPUBLIC OF THE CONGO (EAST AFRICA RIFT)|url=https://www.researchgate.net/publication/323144380|journal=J. Wat. Env. Sci.|volume=1|pages=164–174}}</ref><ref name=":1" /> This includes tingling and burning sensations in the mouth, lips, eyes, and nose because of the acidic nature of CO₂ reacting with surface moisture to form a weak carbonic acid that irritates these soft body parts.<ref name=":38">{{Cite journal|last1=Beaubien|first1=S. E|last2=Ciotoli|first2=G|last3=Lombardi|first3=S|date=2003-04-15|title=Carbon dioxide and radon gas hazard in the Alban Hills area (central Italy)|url=https://linkinghub.elsevier.com/retrieve/pii/S0377027303000283|journal=Journal of Volcanology and Geothermal Research|series=Volcanic hazards: Monitoring, prediction and mitigation|volume=123|issue=1|pages=63–80|bibcode=2003JVGR..123...63B|doi=10.1016/S0377-0273(03)00028-3|issn=0377-0273|url-access=subscription}}</ref><ref name=":31">{{Cite journal|last1=Cantrell|first1=Lee|last2=Young|first2=Michael|date=March 2009|title=Fatal Fall into a Volcanic Fumarole|url=https://journals.sagepub.com/doi/10.1580/08-WEME-CR-199.1|journal=Wilderness & Environmental Medicine|language=en|volume=20|issue=1|pages=77–79|doi=10.1580/08-WEME-CR-199.1|issn=1080-6032|pmid=19364170}}</ref> * Systematic occurrences of dead animals—such as insects, rodents, and reptiles, alongside larger animals like cattle, dogs, and goats—indicate areas of high CO₂ concentration.<ref name=":011" /><ref name=":57" /> * Bulging and swelling of the ground due to pressure caused by CO₂ accumulation.<ref name=":2213" /><ref name=":234">{{Cite journal|last1=Carapezza|first1=Maria Luisa|last2=Tarchini|first2=Luca|last3=Ancona|first3=Carla|last4=Forastiere|first4=Francesco|last5=Ranaldi|first5=Massimo|last6=Ricci|first6=Tullio|last7=De Simone|first7=Gabriele|last8=Mataloni|first8=Francesca|last9=Pagliuca|first9=Nicola Mauro|last10=Barberi|first10=Franco|date=2023-03-01|title=Health impact of natural gas emission at Cava dei Selci residential zone (metropolitan city of Rome, Italy)|journal=Environmental Geochemistry and Health|language=en|volume=45|issue=3|pages=707–729|bibcode=2023EnvGH..45..707C|doi=10.1007/s10653-022-01244-6|issn=1573-2983|pmc=10014802|pmid=35278168}}</ref> These characteristics collectively aid in the identification of mazuku regions in the field.<ref name=":252"/><ref>{{Cite journal|last=Verschuren|first=Jacques|date=18 Jan 2022|title=Jacques Verschuren. Un facteur de mortalité mal connu, l'asphyxie par gaz toxiques naturels au Parc National Albert, Congo.|url=https://hal.science/hal-03531708v1/file/bitstream_119191.pdf|journal=Revue d'Écologie|volume=3|pages=216–237}}</ref>

=== Factors affecting CO₂ levels in mazuku === [[File:Gas Outburst from a well.png|thumb|A well drilled through a pressurized gas pocket triggered a series of CO₂ blowouts along a fault line.]]

CO₂ levels in mazuku areas are affected and influenced by a combination of various factors.

==== Geological factors ==== * '''Increased volcanic and seismic activities:''' CO₂ concentration levels may increase proportionally with volcanic and seismic activities (e.g. earthquakes), which can produce more permeable fractures in the earth's crust, allowing more CO₂ to escape from underground and forming new degassing zones.<ref>{{Cite journal|last1=Zanon|first1=Vittorio|last2=Viveiros|first2=Fátima|date=March 2019|title=A multi-methodological re-evaluation of the volcanic events during the 1580 CE and 1808 eruptions at São Jorge Island (Azores Archipelago, Portugal)|url=https://linkinghub.elsevier.com/retrieve/pii/S0377027318304025|journal=Journal of Volcanology and Geothermal Research|language=en|volume=373|pages=51–67|bibcode=2019JVGR..373...51Z|doi=10.1016/j.jvolgeores.2019.01.028|url-access=subscription}}</ref>

==== Anthropogenic activities ==== * '''Unauthorized well drilling:''' For instance, at [[Colli Albani|Colli Albali volcano]] in [[Italy]], a well was dug through a pressurized gas pocket, causing it to explode. This created a low-pressure zone leading to more CO₂ gas dispersion in the area and resulted in three more gas blowouts along a continuous fault line.<ref name=":234" /> * '''Tarmac roads construction:''' [[Tarmacadam|Tarmac]] roads and concrete surfaces can seal natural gas conduits, blocking the natural flow of gas and leading to its accumulation.<ref name=":2213" /> As trapped gases build up pressure, they can bulge and swell the ground, and release explosively (gas blowout) when they eventually escape. This can cause a road collapse or other infrastructure damage.<ref name=":234" /> * '''Drilling of pit latrines:''' A man died from asphyxiation near the foothills of [[Lake Ngozi|Ngozi volcanic crater]], in the [[Rungwe Volcanic Province]] in [[Tanzania]], while digging a 6m deep [[pit latrine]]. This was likely caused by the accumulation of hazardous gases in the hole after the gas pockets were mechanically disturbed. CO₂ continuously degasses in the area to date, leading to more deaths of birds, cows, and rodents due to the toxic gas buildup.{{Citation needed|date=May 2025}}

==== Meteorological parameters ==== * '''Pressure:''' Pressure variations in the atmosphere have an inverse relationship with CO₂ emissions from the soil; i.e. when the [[atmospheric pressure]] drops the CO₂ emissions are high, but when pressure rises the CO₂ emissions are lower.<ref name=":95" /><ref name=":234" /> * '''Wind speed:''' Low wind speed decreases the chance of CO₂ dispersion to the atmosphere and allows heavy gases to accumulate in low-lying areas like valleys and depressions.<ref name=":247" /><ref name=":274" /><ref name=":304" /> * '''Soil moisture content and season:''' During heavy winter rains, subsurface soil voids are totally filled with water, into which dissolve a significant amount of CO₂. In contrast, when the soil is dry during summer, these voids remain empty and can accumulate large amounts of degassed CO₂, which can escape and fill in low-lying areas, posing great health risks.<ref name=":247" /><ref name=":292" /> * '''Time of day:''' At night, with no solar radiation and reduced solar intensity, atmospheric temperatures drop and wind speeds decrease significantly.<ref name=":274" /> These conditions slow the dispersal of heavy gases, causing them to accumulate in low-lying areas.<ref name=":322" /> During the day, sunlight heats the air, creating low pressure that allows CO₂ emissions to rise and disperse, reducing the risk of dangerous concentration levels.<ref name=":2213" /><ref name=":304" />

== CO₂ exposure health effects and international guideline limits == The health hazards linked to both short-term and long-term exposure of lethal doses of CO₂ in mazuku are outlined in the table below, along with permissible exposure limits (PELs) for CO₂ to promote safety in workplaces and for residents near active volcanic areas. These limits specify safe exposure durations at various concentrations to help prevent health risks over time.

{|class="wikitable" !CO₂ concentration % (mixed with air) !Short term exposure effects !Long term exposure effects !Average time of exposure |- |0–1.5% |Mostly unnoticed by [[olfactory]] or visual senses<ref name=":2213"/> |More noticeable conditions such as shortness of breath, lightheadedness, and dizziness |8 hours maximum exposure |- |1.5–6% |Difficulty in breathing, increased heart rate, [[dyspnoea]] (shortness of breath)<ref name=":2213"/> |Tingling sensations in lips, eyes, and nose because of the acidic nature of CO₂, which reacts with surface moisture to form a weak carbonic acid that irritates these soft body parts<ref name=":38"/><ref name=":31"/> |15 minutes maximum exposure |- |6–10% |Dizziness, buzzing sound in ears, lightheadedness, muscular and joint weakness, drowsiness, headaches, sweating, shortness of breath, low mood and mental distress, fainting, increased heart rate<ref name=":322">{{Cite journal|last1=Camarinho|first1=Ricardo|last2=Garcia|first2=Patrícia Ventura|last3=Rodrigues|first3=Armindo Santos|date=2013-10-01|title=Chronic exposure to volcanogenic air pollution as cause of lung injury|url=https://linkinghub.elsevier.com/retrieve/pii/S0269749113003126|journal=Environmental Pollution|volume=181|pages=24–30|bibcode=2013EPoll.181...24C|doi=10.1016/j.envpol.2013.05.052|issn=0269-7491|pmid=23800425|url-access=subscription}}</ref> |Dizziness and loss of consciousness<ref name=":332">{{Citation|last1=Williams-Jones|first1=Glyn|title=Chapter 57 - Hazards of Volcanic Gases|date=2015-01-01|pages=985–992|editor-last=Sigurdsson|editor-first=Haraldur|url=https://linkinghub.elsevier.com/retrieve/pii/B9780123859389000572|access-date=2024-10-25|place=Amsterdam|publisher=Academic Press|doi=10.1016/b978-0-12-385938-9.00057-2|isbn=978-0-12-385938-9|last2=Rymer|first2=Hazel|encyclopedia=The Encyclopedia of Volcanoes (Second Edition)|url-access=subscription}}</ref> |Tolerable within a span of several minutes |- |11–15% |Severe abrupt muscle contractions, caused because body cells lack enough oxygen for respiration and subsequently become unconscious within few seconds.<ref name=":342">{{Cite journal|last=Langford|first=Nigel J.|date=2005-12-01|title=Carbon Dioxide Poisoning|url=https://link.springer.com/article/10.2165/00139709-200524040-00003|journal=Toxicological Reviews|language=en|volume=24|issue=4|pages=229–235|doi=10.2165/00139709-200524040-00003|issn=1176-2551|pmid=16499405|url-access=subscription}}</ref> |Severe muscle cramps and loss of consciousness<ref name=":31"/> |Death in less than a minute |- |˃&nbsp;25% |Intolerable amount of CO₂ for full functioning of the human body. Generally a victim suffers convulsions, coma, and finally death.<ref name=":322"/> |Convulsions, coma, and death<ref name=":342"/> |Death in less than a minute |}

== Case studies == Mazuku occur in various parts of the world where volcanic or geologically active regions release CO₂-rich gases. These gases accumulate in low-lying areas, valleys, or confined spaces or in the stratified water layers of [[meromictic lake]]s, creating hazardous conditions and deadly [[asphyxiation]] zones for humans, wildlife, and plants. The following are case studies.

=== Lake Monoun === [[Lake Monoun]] is a volcanic crater lake situated in the [[Oku Volcanic Field]], which is part of the [[Cameroon line|Cameroon Volcanic Line]]. It was formed when a lava flow created a natural barrier.<ref name=":332"/><ref name=":153">{{Cite journal|last=Sigurdsson|first=Haraldur|date=June 1988|title=Gas Bursts from Cameroon Crater Lakes: A New Natural Hazard|url=https://onlinelibrary.wiley.com/doi/10.1111/j.1467-7717.1988.tb00661.x|journal=Disasters|language=en|volume=12|issue=2|pages=131–146|bibcode=1988Disas..12..131S|doi=10.1111/j.1467-7717.1988.tb00661.x|issn=0361-3666|pmid=20958652|url-access=subscription}}</ref> In 1984, the lake experienced a deadly gas exsolution, triggering a violent [[limnic eruption]] that killed 37 people.<ref name=":011"/><ref name=":153"/> The primary source of the gas was volcanic CO₂ emissions, confirmed by carbon isotope signatures, which had accumulated in the lake's stratified waters over time, leading to increased pressure.<ref name=":111"/><ref name=":153"/> Seismic activity and an underwater landslide were responsible for the disturbance of the lake's stratification, releasing the trapped CO₂ violently and causing a very dangerous gas outburst.<ref name=":153"/><ref name=":1"/>

=== Lake Nyos === [[File:Cow killed by Lake Nyos gasses.jpg|thumb|Cow suffocated and killed by CO₂ during Lake Nyos limnic eruption in Cameroon, 1986]]

A similar scenario occurred two years later in 1986 at [[Lake Nyos]], another crater lake in Cameroon, often referred to as a "killer lake".<ref name=":1"/><ref name=":262"/> The lake experienced a catastrophic [[limnic eruption]], also known as a "lake overturn", a rare phenomenon in which dissolved volcanic gases are released from the stratified bottom layers of lakes after a mechanical disturbance.<ref name=":611"/> The ensuing sudden release of an overwhelming amount of CO₂ led to the deaths of 1,700 people and 300 cattle.<ref name=":1"/><ref name=":332"/>

Geologically, the crater lake sits over a network of active faults and lineaments and is fed underneath by volatile-rich basaltic dikes.<ref name=":1"/> These dikes release magmatic gases and volatiles like CO₂ and H₂O, which, upon their release at low pressure, likely contributed to a [[Phreatomagmatic eruption|phreatomagmatic]] [[explosive eruption]] that formed a [[diatreme]]<ref>{{Cite journal|last1=White|first1=J. D. L.|last2=Ross|first2=P. -S.|date=2011-04-15|title=Maar-diatreme volcanoes: A review|url=https://linkinghub.elsevier.com/retrieve/pii/S0377027311000357|journal=Journal of Volcanology and Geothermal Research|series=From maars to scoria cones: the enigma of monogenetic volcanic fields|volume=201|issue=1|pages=1–29|bibcode=2011JVGR..201....1W|doi=10.1016/j.jvolgeores.2011.01.010|issn=0377-0273}}</ref> beneath the lake and a [[maar]] depression on the surface.<ref name=":1"/>

Normally, a mazuku involves dry CO₂ gas seeping through fissures and accumulating in low-lying areas before dispersing into the atmosphere.<ref name=":011"/> However, when gas columns are obstructed by rock strata, such as thick pyroclastic deposits or the stratified water of [[meromictic lake]]s, the gases remain trapped or dissolved, respectively, in the lake waters.<ref name=":137"/><ref name=":611"/> The [[Lake Nyos disaster]] is an example of the latter, when CO₂-rich gas significantly accumulated in the water under extreme pressure.<ref name=":1"/>

It is believed that a landslide triggered the exsolution of the dissolved gases, which caused a limnic eruption.<ref name=":1"/> As a result, a massive CO₂ cloud (about 98% CO₂ by volume) rose from the lake's floor (208m deep), spread over and down the valleys, engulfed the nearby villages, and killed everything by asphyxiation.<ref name=":1"/><ref name=":611"/>

=== Mammoth Mountain === [[Mammoth Mountain]], a [[Volcano|dormant volcano]] in the [[Sierra Nevada]] region of California, United States, is underlaid by a shallow [[dacite|dacitic]] dome that releases cold and dry CO₂-rich gases (98v% CO₂) through [[fumarole]] vents and fractures located on the flanks of the mountain.<ref name=":95"/><ref name=":10">{{Cite journal|last1=Gerlach|first1=T. M.|last2=Doukas|first2=M. P.|last3=McGee|first3=K. A.|last4=Kessler|first4=R.|date=1999-12-15|title=Airborne detection of diffuse carbon dioxide emissions at Mammoth Mountain, California|url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/1999GL008388|journal=Geophysical Research Letters|language=en|volume=26|issue=24|pages=3661–3664|bibcode=1999GeoRL..26.3661G|doi=10.1029/1999GL008388|issn=0094-8276}}</ref><ref name=":11">{{Cite journal|last=Hill|first=Peter M.|date=September 2000|title=Possible asphyxiation from carbon dioxide of a cross-country skier in eastern California: a deadly volcanic hazard|url=https://journals.sagepub.com/doi/full/10.1580/1080-6032(2000)011[0192:PAFCDO]2.3.CO;2|journal=Wilderness & Environmental Medicine|language=en|volume=11|issue=3|pages=192–195|doi=10.1580/1080-6032(2000)011[0192:PAFCDO]2.3.CO;2|pmid=11055566|url-access=subscription}}</ref> The gas fluxes were estimated at a rate of ~1,200 tonnes per day, comparable to gas fluxes observed at the summit craters of [[Kīlauea]] in Hawaii, [[Mount Etna]] in [[Italy]], and [[Mount St. Helens]] in Washington.<ref name=":122">{{Cite journal|last1=Farrar|first1=C. D.|last2=Sorey|first2=M. L.|last3=Evans|first3=W. C.|last4=Howle|first4=J. F.|last5=Kerr|first5=B. D.|last6=Kennedy|first6=B. M.|last7=King|first7=C.-Y.|last8=Southon|first8=J. R.|date=August 1995|title=Forest-killing diffuse CO2 emission at Mammoth Mountain as a sign of magmatic unrest|url=https://www.nature.com/articles/376675a0|journal=Nature|language=en|volume=376|issue=6542|pages=675–678|doi=10.1038/376675a0|issn=1476-4687|url-access=subscription}}</ref> The CO₂ originates from deeper magmatic sources (as evidenced from He-CO₂ isotopic signature) at about 10&nbsp;km below the surface, and travels through permeable networks of fractures and faults.<ref name=":11"/><ref name=":332"/> The CO₂-rich gases accumulate in the soil layers at depths between 0.6–1m, in closed subsurface cavities, and in snow caves, suggesting an ongoing active magmatic activity beneath the mountain.<ref name=":95"/>

[[File:Death_by_Carbon_Dioxide,_Horseshoe_Lake,_Mammoth,_CA_2016_(32011250720).jpg|thumb|Dead trees at [[Mammoth Mountain]] in California due to increased CO₂ levels in the soil, leading to toxic acidity and effects on plant health]]

One visible manifestation of this toxic degassing is the large-scale mortality of [[Conifer|coniferous trees]], covering an area of up to 100 hectares on the mountain's flanks.<ref name=":10"/><ref name=":122"/> The accumulation of CO₂ in closed depressions and subsurface soil layers exposes tree roots to toxic gases, leading to widespread tree death.<ref name=":31"/><ref name=":11"/> In addition to CO₂ poisoning, the trees are affected by highly altered and [[Soil pH|acidic soils]].<ref name=":122"/> The region also experiences frequent [[earthquake]]s, often with up to magnitudes of 6 on the [[Richter scale]].<ref name=":11"/><ref name=":122"/> These seismic events, combined with the mountain's bulging and exhumation, fracture the surface and allow high-pressure volatiles to escape, further releasing CO₂ into the zone.<ref name=":122"/>

=== Monte Amiata === [[Monte Amiata]] is a dormant volcano located in [[Tuscany]], central Italy, known for its significant emissions of dry and cold CO₂-rich gases, which are primarily magmatic in origin.<ref name=":172">{{Cite journal|last1=Tassi|first1=F.|last2=Vaselli|first2=O.|last3=Cuccoli|first3=F.|last4=Buccianti|first4=A.|last5=Nisi|first5=B.|last6=Lognoli|first6=E.|last7=Montegrossi|first7=G.|date=April 2009|title=A Geochemical Multi-Methodological Approach in Hazard Assessment of CO2-Rich Gas Emissions at Mt. Amiata Volcano (Tuscany, Central Italy)|url=http://link.springer.com/10.1007/s11267-008-9198-2|journal=Water, Air, & Soil Pollution: Focus|language=en|volume=9|issue=1–2|pages=117–127|bibcode=2009WASPF...9..117T|doi=10.1007/s11267-008-9198-2|issn=1567-7230|url-access=subscription}}</ref> The gases originate from the deep geothermal system beneath the volcano and pass through a permeable network of faults and fractures by passive mechanism degassing processes.<ref name=":182">{{Cite journal|last1=Minissale|first1=Angelo|last2=Evans|first2=Williams C.|last3=Magro|first3=Gabriella|last4=Vaselli|first4=Orlando|date=1997-10-22|title=Multiple source components in gas manifestations from north-central Italy|url=https://linkinghub.elsevier.com/retrieve/pii/S0009254197000818|journal=Chemical Geology|volume=142|issue=3|pages=175–192|bibcode=1997ChGeo.142..175M|doi=10.1016/S0009-2541(97)00081-8|issn=0009-2541|url-access=subscription}}</ref><ref>{{Cite journal|last1=Chiodini|first1=G.|last2=Baldini|first2=A.|last3=Barberi|first3=F.|last4=Carapezza|first4=M. L.|last5=Cardellini|first5=C.|last6=Frondini|first6=F.|last7=Granieri|first7=D.|last8=Ranaldi|first8=M.|date=December 2007|title=Carbon dioxide degassing at Latera caldera (Italy): Evidence of geothermal reservoir and evaluation of its potential energy|url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2006JB004896|journal=Journal of Geophysical Research: Solid Earth|language=en|volume=112|issue=B12|bibcode=2007JGRB..11212204C|doi=10.1029/2006JB004896|issn=0148-0227}}</ref> Although the area has not experienced recent volcanic eruptions, it remains geothermally active, with CO₂ emissions contributing to environmental risks like [[soil acidification]] and potential CO₂ build-up in low-lying areas, posing hazards to local wildlife and humans.<ref name=":172"/> The region is also notable for its significance in geothermal energy production, and gas emissions are closely monitored to assess both volcanic hazards and energy sustainability.<ref name=":182"/>

=== Mount Sinila === [[File:Area Kawah Sikidang, Dieng Plateau.jpg|thumb|Dry CO₂ emissions observed on the [[Dieng Plateau|Diëng Plateau]], Indonesia, highlight volcanic activity and the potential hazards of gas releases.]]

[[Mt. Sinila]] is a volcanic mountain located on the [[Dieng Plateau|Diëng Plateau]] in Indonesia. In 1979 it experienced a tragic [[phreatic eruption]] disaster when a mixture of steam, lahar, and toxic gases was released from the open cracks and fissures located near the crater and gushed down the valley, asphyxiating insects, rodents, goats, dogs, and cows, as well as claiming the lives of 172 people.{{citation needed|date=November 2024}} Before the eruption, the area experienced a series of earthquakes that reactivated ancient fractures over the span of a few hours.<ref name=":292">{{Cite journal|last1=Allard|first1=P.|last2=Dajlevic|first2=D.|last3=Delarue|first3=C.|date=November 1989|title=Origin of carbon dioxide emanation from the 1979 Dieng eruption, Indonesia: Implications for the origin of the 1986 Nyos catastrophe|url=https://linkinghub.elsevier.com/retrieve/pii/0377027389900589|journal=Journal of Volcanology and Geothermal Research|language=en|volume=39|issue=2–3|pages=195–206|bibcode=1989JVGR...39..195A|doi=10.1016/0377-0273(89)90058-9|url-access=subscription}}</ref> After a few hours during the main course of eruption, dry gas was emitted from a new 1,000m-long fissure that had emerged on the western flank of the volcano near [[Sumur crater]].<ref name=":19"/> Gas analysis revealed that the dry gas was CO₂-rich from magmatic sources, with concentrations reaching up to 99% by volume.<ref name=":19"/><ref name=":292"/> Since CO₂ is heavier than air, it flowed down the valley, displacing oxygen and hugging the ground like fog.<ref name=":3"/><ref name=":5"/> All victims were found dead in a linear path of gas flow, likely caught them off guard as they slept, with the gas suffocating them simultaneously.<ref name=":6"/><ref name=":19"/><ref name=":292"/>

== Effects == [[File:Wild animals killed by mazuku.png|thumb|Diffuse CO₂ gas emissions forming mazuku zones in [[Virunga National Park]] (DRC) have killed wild animals, including elephants, hyenas, and baboons.]]

Depending on their gas composition and concentration, mazuku can cause various effects on flora and fauna.<ref name=":316"/> Massive clouds of CO₂, such as those released from lakes in the 1980s, can cause widespread devastation of human and wildlife populations.<ref name=":57"/> Local vegetation is typically not very strongly affected.<ref name=":153"/><ref name=":1"/> If the concentration of CO₂ is high enough and maintained in a prolonged outgassing event, however, even vegetation can be affected by the mazuku, as is the case on [[Mammoth Mountain]], where deforestation has occurred, as well as CO₂ poisonings, including the deaths of two skiers, one in 1995 and one in 1998.<ref name=":122"/><ref name=":11"/><ref name=":31"/>

In some cases, mazuku are large enough to cause localized flora and fauna extinction events that are documented in the [[fossil]] record.<ref name=":19">{{Cite journal|last1=Ross|first1=Kelly Ann|last2=Smets|first2=Benoît|last3=De Batist|first3=Marc|last4=Hilbe|first4=Michael|last5=Schmid|first5=Martin|last6=Anselmetti|first6=Flavio S.|date=2014-09-15|title=Lake-level rise in the late Pleistocene and active subaquatic volcanism since the Holocene in Lake Kivu, East African Rift|url=https://linkinghub.elsevier.com/retrieve/pii/S0169555X14002608|journal=Geomorphology|volume=221|pages=274–285|bibcode=2014Geomo.221..274R|doi=10.1016/j.geomorph.2014.05.010|issn=0169-555X}}</ref> For example, sediment core [[radiocarbon dating]] records from [[Lake Kivu]] have shown a sequence of repeated and regular massive lake overturn events approximately every 800–1000 years that were caused by methane explosions and tsunamis due to accumulation of magmatic CO₂.<ref name=":3">{{Cite journal|last1=Pasche|first1=Natacha|last2=Schmid|first2=Martin|last3=Vazquez|first3=Francisco|last4=Schubert|first4=Carsten J.|last5=Wüest|first5=Alfred|last6=Kessler|first6=John D.|last7=Pack|first7=Mary A.|last8=Reeburgh|first8=William S.|last9=Bürgmann|first9=Helmut|date=2011-07-22|title=Methane sources and sinks in Lake Kivu|url=http://doi.wiley.com/10.1029/2011JG001690|journal=Journal of Geophysical Research|language=en|volume=116|issue=G3|article-number=G03006 |bibcode=2011JGRG..116.3006P|doi=10.1029/2011JG001690|issn=0148-0227}}</ref>

If mazuku occurs underneath lakes, it can lead to changes in water chemistry, creating [[meromictic lake]]s that are dangerous for aquatic life.<ref name=":611"/> For example, the buildup of CO₂ in [[Lake Kivu]], [[Lake Nyos]], and [[Lake Monoun]] caused stratification and oxygen depletion, affecting fish and other organisms living in the water.<ref name=":011"/><ref name=":153"/>

=== Summary === {| class="wikitable" ! !Country !Volcanic structure !Year occurred !Volcano state !CO₂ release events !Measured CO₂ conc. !Environmental effects !Casualties |- |1 |[[DRC]] and [[Rwanda]] |Virunga Volcanic Province

* Mt.&nbsp;Nyiragongo<ref name=":2213" /><ref name=":247" /> * Mt.&nbsp;Nyamulagira<ref name=":011" /><ref name=":316" /> |1900s to present |Active |Dry CO₂ degassing |90% |Acidic soil, death of animals due to ˃&nbsp;500,000 ppm of CO₂ in the soil |~13 deaths per year |- |2 |DRC |Virunga Volcanic Province

* Lake Kivu<ref name=":111" /> |1900s to present |Active |Diffuse outgassing of CO₂ into the lake water |˃&nbsp;25% |Water chemistry alteration, habitat disruption, loss of biodiversity |Dizziness and convulsions lead to 2 swimmers drowning; potential future catastrophic limnic eruption |- |3 |[[Cameroon]]<ref name=":5">{{Cite journal|last=Wagner|first=G N|date=July 1988|title=Medical evaluation of the victims of the 1986 Lake Nyos disaster|journal=J Forensic Sci|volume=33|issue=4|pages=899–909|doi=10.1520/JFS12512J|pmid=3139823}}</ref> |Cameroon Volcanic Line

* Lake Monoun |1984 |Active |[[Limnic eruption]] |96.73% |Water chemistry alteration, habitat disruption, loss of biodiversity |37 people died |- |4 |Cameroon |Cameroon Volcanic Line

* Lake Nyos<ref name=":011" /><ref name=":1" /> |1986 |Active |Limnic eruption |98% |Water chemistry alteration, habitat disruption, loss of biodiversity |1,700 deaths |- |5 |[[United States]] |Mammoth Mountain<ref name=":11"/><ref name=":247"/><ref name=":122"/><ref name=":31"/> |1998 |Dormant |Dry diffuse CO₂ through the soil |98% |Acidic soil, barren land (~100 hectares in a tree-kill area and dead animals) |A skier died from acute [[Swimming-induced pulmonary edema|pulmonary edema]] in a snow cave with ~98% CO₂ |- |6 |[[Indonesia]] |Diëng Plateau

* Mt. Sinila<ref name=":215" /> |1979 |Dormant |[[Phreatic eruption]] |99% |Tree kill zones due to acidic soils; dead reptiles and rodents |172 people died |- |7 |[[Tanzania]] |Rungwe Volcanic Province

* Mt.&nbsp;Rungwe<ref name=":215" /> * Mt.&nbsp;Ngozi<ref name=":4" /><ref name=":6">{{Cite journal|last=Jolie|first=Egbert|date=2019-08-21|title=Detecting gas-rich hydrothermal vents in Ngozi Crater Lake using integrated exploration tools|journal=Scientific Reports|language=en|volume=9|issue=1|article-number=12164|bibcode=2019NatSR...912164J|doi=10.1038/s41598-019-48576-5|issn=2045-2322|pmc=6704129|pmid=31434949}}</ref> |2001, 2004 and 2022 |Dormant |Dry CO₂ degassing |95% |Tree kill zones due to acidic soils; dead reptiles and rodents |1 man died while digging a pit latrine; 2 men died when they fell into a ditch |- |8 |[[Italy]] |Vulcano Island<ref>{{Cite journal|last=Baubron|first=JC|date=1 March 199|title=Diffuse volcanic emissions of carbon dioxide from Vulcano Island, Italy|url=https://www.nature.com/articles/344051a0|journal=Nature|volume=344|issue=6261|pages=51–53|bibcode=1990Natur.344...51B|doi=10.1038/344051a0|pmid=18278024|url-access=subscription}}</ref><ref>{{Cite journal|last=Baxter|first=Peter J.|date=1990-09-01|title=Medical effects of volcanic eruptions|url=https://link.springer.com/article/10.1007/BF00301534|journal=Bulletin of Volcanology|language=en|volume=52|issue=7|pages=532–544|doi=10.1007/BF00301534|issn=1432-0819|url-access=subscription}}</ref><ref name=":262">{{Cite journal|last1=Hansell|first1=Anna|last2=Oppenheimer|first2=Clive|date=December 2004|title=Health Hazards from Volcanic Gases: A Systematic Literature Review|url=http://www.tandfonline.com/doi/abs/10.1080/00039890409602947|journal=Archives of Environmental Health|language=en|volume=59|issue=12|pages=628–639|doi=10.1080/00039890409602947|issn=0003-9896|pmid=16789471|url-access=subscription}}</ref> |1980 |Active |Diffuse CO₂ on mountain flanks |50% |Tree kill zones due to acidic soils; dead reptiles and rodents |2 children died from asphyxiation |- |9 |Italy |Lazio and Alban Hills<ref>{{Cite journal|last1=Annunziatellis|first1=A|last2=Ciotoli|first2=G|last3=Lombardi|first3=S|last4=Nolasco|first4=F|date=2003-03-01|title=Short- and long-term gas hazard: the release of toxic gases in the Alban Hills volcanic area (central Italy)|url=https://linkinghub.elsevier.com/retrieve/pii/S0375674202002728|journal=Journal of Geochemical Exploration|volume=77|issue=2|pages=93–108|bibcode=2003JCExp..77...93A|doi=10.1016/S0375-6742(02)00272-8|issn=0375-6742|url-access=subscription}}</ref><ref>{{Cite journal|last1=Carapezza|first1=M. L.|last2=Badalamenti|first2=B.|last3=Cavarra|first3=L.|last4=Scalzo|first4=A.|date=2003-04-15|title=Gas hazard assessment in a densely inhabited area of Colli Albani Volcano (Cava dei Selci, Roma)|url=https://linkinghub.elsevier.com/retrieve/pii/S0377027303000295|journal=Journal of Volcanology and Geothermal Research|series=Volcanic hazards: Monitoring, prediction and mitigation|volume=123|issue=1|pages=81–94|bibcode=2003JVGR..123...81C|doi=10.1016/S0377-0273(03)00029-5|issn=0377-0273|url-access=subscription}}</ref> |2000 |Dormant |Dry diffuse CO₂ through the soil |92.7% |Tree kill zones due to acidic soils; dead reptiles and rodents |1 man died when he fell into an abandoned well |- |10 |Italy |Alban Hills<ref>{{Cite journal|last1=Carapezza|first1=M. L.|last2=Barberi|first2=F.|last3=Ranaldi|first3=M.|last4=Ricci|first4=T.|last5=Tarchini|first5=L.|last6=Barrancos|first6=J.|last7=Fischer|first7=C.|last8=Granieri|first8=D.|last9=Lucchetti|first9=C.|last10=Melian|first10=G.|last11=Perez|first11=N.|last12=Tuccimei|first12=P.|last13=Vogel|first13=A.|last14=Weber|first14=K.|date=2012-09-01|title=Hazardous gas emissions from the flanks of the quiescent Colli Albani volcano (Rome, Italy)|url=https://linkinghub.elsevier.com/retrieve/pii/S0883292712000455|journal=Applied Geochemistry|series=13th International Symposium on Water-Rock Interaction (WRI -13)|volume=27|issue=9|pages=1767–1782|bibcode=2012ApGC...27.1767C|doi=10.1016/j.apgeochem.2012.02.012|issn=0883-2927|url-access=subscription}}</ref><ref name=":262"/>

* Cava dei Selci<ref name=":234" /> |2011 |Dormant |Dry diffuse CO₂ through the soil |99% |Cows and pets died from [[Asphixiation|asyphixiation]]; gas blowouts, ground swells, and roads collapses |3 people died in an open spa |- |11 |[[Japan]] |[[Hakkōda Mountains|Hakkoda]]<ref>{{Cite journal|last1=Hernández Perez|first1=Pedro|last2=Notsu|first2=Kenji|last3=Tsurumi|first3=Makoto|last4=Mori|first4=Toshiya|last5=Ohno|first5=Masao|last6=Shimoike|first6=Yoichi|last7=Salazar|first7=Jose|last8=Pérez|first8=Nemesio|date=April 2003|title=Carbon dioxide emissions from soils at Hakkoda, north Japan|url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2002JB001847|journal=Journal of Geophysical Research: Solid Earth|language=en|volume=108|issue=B4|page=2210|bibcode=2003JGRB..108.2210H|doi=10.1029/2002JB001847|issn=0148-0227}}</ref><ref>{{Cite journal|last1=Hutchison|first1=William|last2=Ogilvie|first2=Euan R. D.|last3=Birhane|first3=Yafet G.|last4=Barry|first4=Peter H.|last5=Fischer|first5=Tobias P.|last6=Ballentine|first6=Chris J.|last7=Hillegonds|first7=Darren J.|last8=Biggs|first8=Juliet|last9=Albino|first9=Fabien|last10=Cervantes|first10=Chelsea|last11=Guðbrandsson|first11=Snorri|date=April 2023|title=Gas Emissions and Subsurface Architecture of Fault-Controlled Geothermal Systems: A Case Study of the North Abaya Geothermal Area|journal=Geochemistry, Geophysics, Geosystems|language=en|volume=24|issue=4|bibcode=2023GGG....2410822H|doi=10.1029/2022GC010822|issn=1525-2027|doi-access=free}}</ref><ref>{{Cite journal|date=1997|title=Report on Hakkodasan (Japan)|editor1-last=Wunderman|editor1-first=Richard|others=Bulletin of the Global Volcanism Network|volume=22|issue=6|publisher=Smithsonian Institution|doi=10.5479/si.GVP.BGVN199706-283280|journal=Bulletin of the Global Volcanism Network}}</ref><ref name=":262"/> |1997 |Dormant |Dry diffuse CO₂ through the soil into depressions |15–20% |Bare land and a pattern of dead animals were observed |3 soldiers died after falling into a depression |- |12 |[[Portugal]] |[[Furnas]], São Miguel, Azores<ref>{{Cite journal|last1=Baxter|first1=Peter J|last2=Baubron|first2=Jean-Claude|last3=Coutinho|first3=Rui|date=1999-09-01|title=Health hazards and disaster potential of ground gas emissions at Furnas volcano, São Miguel, Azores|url=https://linkinghub.elsevier.com/retrieve/pii/S0377027399000700|journal=Journal of Volcanology and Geothermal Research|volume=92|issue=1|pages=95–106|bibcode=1999JVGR...92...95B|doi=10.1016/S0377-0273(99)00070-0|issn=0377-0273|url-access=subscription}}</ref> |1999 |Active |Dry diffuse CO₂ through the soil |99% |Tree kill zones due to acidic soils; dead reptiles and rodents |3 people died from asphyxiation in house cellars and a well |}

== Hazard assessment and mitigation ==

=== Hazard assessment === Areas experiencing mazuku emissions face multiple forms of hazards due to their proximity to active volcanoes.

==== Continuous hazards ==== These are long-lasting volcanic hazards that persist for extended periods of time, even without an active volcanic eruption.<ref name=":011"/> For instance, in regions near active volcanoes, such as the [[Virunga Mountains|Virunga Volcanic Province]], people, livestock, and wildlife in low-lying areas are silently asphyxiated by mazuku gases.<ref name=":2213"/> The danger from mazuku remains constant, posing a long-term threat to communities living in these volcanic zones.

Long-term exposure to mazuku can lead to environmental degradation and [[Biodiversity loss|loss of biodiversity]].<ref name=":19"/> Agricultural lands may be impacted by CO₂ accumulation in subsurface layers of soils, creating toxic acidic soil and leading to crop failures and economic disruption.<ref name=":122" />

==== Latent hazards ==== Latent hazards are dormant threats that require an external trigger, such as a mechanical disturbance, to become dangerous and deadly under specific conditions. For example, [[Meromictic lake|meromictic]] lakes like [[Lake Nyos]], [[Lake Kivu]], and [[Lake Monoun]] can contain enormous amounts of dissolved carbon dioxide (and sometimes methane) in their deep stratified layers ([[monimolimnion]]).<ref name=":137"/><ref name=":611"/><ref name=":153"/> Under normal conditions, these gases remain trapped in the lower layers of the lake.<ref name=":1"/> However, if triggered by an external mechanical disturbance such as volcanic activity, an earthquake, or a landslide, these gases can release explosively in a [[limnic eruption]]. This could lead to widespread asphyxiation and fires across the surrounding regions.<ref name=":011"/><ref name=":1"/>

Mazuku may also indicate deeper magmatic unrest, warning of further natural disasters such as earthquakes, volcanic eruptions, and landslides.<ref name=":011"/>

=== Mitigation measures === Due to the silent (colorless and odorless) and deadly nature of CO₂ in volcanic active areas, authorities must be proactive and prepared to combat this natural hazard and reduce its hazardous effects. Some of the mitigation measures are:

'''On-ground CO₂ detection sensors:''' Early warning systems can be installed in high-risk areas. For example, at Mt. Amiata in Italy, researchers employ soil CO₂ flux sensors to measure diffuse CO₂ emissions with a notable flux measurement of about 13,000 tons/day.<ref name=":172"/>

[[File:Lake nyos co2 vent.jpg|thumb|Artificial siphoning at [[Lake Nyos]] safely releases CO₂ from deep lake layers, preventing pressure buildup and reducing the risk of a [[limnic eruption]]]]

'''Volcano geoengineering technologies:''' Human-induced degassing technologies can be employed in [[meromictic lake]]s to prevent the sudden natural release of gases. For instance, at Lake Nyos, siphons were installed to lower gas pressure by extracting CO₂-rich water from the lake's bottom saline layers.<ref name=":137"/><ref name=":20">{{Cite journal|last1=Cassidy|first1=Michael|last2=Sandberg|first2=Anders|last3=Mani|first3=Lara|date=October 2023|title=The Ethics of Volcano Geoengineering|url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2023EF003714|journal=Earth's Future|language=en|volume=11|issue=10|bibcode=2023EaFut..1103714C|doi=10.1029/2023EF003714|issn=2328-4277}}</ref> This process enables the dissolved carbon dioxide to escape into the atmosphere as the water rises to the surface. By reducing the concentration of dissolved gases, this method decreases the risk of catastrophic [[limnic eruption]]s, like the one happened in 1986. The siphon system effectively promotes controlled gas exsolution, preventing dangerous pressure build-up.<ref name=":20"/>

'''Land-use planning:''' Town planners can indicate buffer zones which are prone to mazuku and prevent settlements in these areas.

[[File:Co2-danger-area-ahead-sign 1600.jpg|thumb|A hazard sign indicating high CO₂ concentration at Mammoth Mountain in California, emphasizing danger and the need to take precaution when visiting these areas]]

'''Relocation and closing high CO₂-concentrated areas:''' For essential community safety, there should be immediate evacuation plans and warning signs in hazardous places.<ref name=":234"/>

'''Developing gas hazard and risk maps:''' Key CO₂ data—such as [[soil gas]] concentrations, carbon isotopes (which help trace CO₂ sources), and CO₂ flux levels—should be collected in volcanic areas prone to mazuku.<ref name=":2213"/> Mapping these areas through gas concentration and flux measurements can greatly help during construction and settlement allocation decisions.<ref name=":247"/><ref name=":234"/>

'''Education and sensitization campaigns:''' There should be continued scientific research on CO₂ emissions in volcanic active regions, including the creation and improvement of existing CO₂ dispersion models on the causes and occurrence of mazuku.<ref>{{Cite journal|last1=Massaro|first1=Silvia|last2=Dioguardi|first2=Fabio|last3=Sandri|first3=Laura|last4=Tamburello|first4=Giancarlo|last5=Selva|first5=Jacopo|last6=Moune|first6=Séverine|last7=Jessop|first7=David E.|last8=Moretti|first8=Roberto|last9=Komorowski|first9=Jean-Christophe|last10=Costa|first10=Antonio|date=September 2021|title=Testing gas dispersion modelling: A case study at La Soufrière volcano (Guadeloupe, Lesser Antilles)|url=https://linkinghub.elsevier.com/retrieve/pii/S0377027321001414|journal=Journal of Volcanology and Geothermal Research|language=en|volume=417|article-number=107312|bibcode=2021JVGR..41707312M|doi=10.1016/j.jvolgeores.2021.107312}}</ref>

== Mazuku's influence on climate ==

Volcanic mountains such as Mount Etna in Italy, Kilauea in Hawaii, Nyiragongo and Nyamulagira in Congo, and their adjoining areas are significant sources of magma-derived gases, releasing massive amounts of CO₂ both during eruptions and through continuous magma upwelling (passive degassing) in non-eruptive states through fumaroles, hot springs, and gas plumes.<ref name=":37"/> {{failed verification span|text=For instance, during active eruptions, Mount Etna in Italy can emit up to 61,800 tons of CO₂ per day. Even when not erupting, it is still passively degassing and it can emit around 137 tons of CO₂ per day.<ref name=":352">{{Cite journal|last1=Aiuppa|first1=A.|last2=Federico|first2=C.|last3=Giudice|first3=G.|last4=Gurrieri|first4=S.|last5=Liuzzo|first5=M.|last6=Shinohara|first6=H.|last7=Favara|first7=R.|last8=Valenza|first8=M.|date=September 2006|title=Rates of carbon dioxide plume degassing from Mount Etna volcano|url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2006JB004307|journal=Journal of Geophysical Research: Solid Earth|language=en|volume=111|issue=B9|bibcode=2006JGRB..111.9207A|doi=10.1029/2006JB004307|issn=0148-0227}}</ref>|reason="up to 61,800 tons" and "around 137 tons" are not mentioned in the cited source reference.|date=May 2025}} The cycling of CO₂ and other gases—such as [[sulfur dioxide]], hydrogen sulfide, water vapor, and hydrogen chloride—is driven by magma convection, where degassed magma sinks, recharges with CO₂ at depth, and rises again, ensuring a constant supply of volatile-rich magma, a process likely fueled by a mantle source beneath.<ref>{{Cite journal|last1=Blundy|first1=J.|last2=Mavrogenes|first2=J.|last3=Tattitch|first3=B.|last4=Sparks|first4=S.|last5=Gilmer|first5=A.|date=March 2015|title=Generation of porphyry copper deposits by gas–brine reaction in volcanic arcs|url=https://www.nature.com/articles/ngeo2351|journal=Nature Geoscience|language=en|volume=8|issue=3|pages=235–240|bibcode=2015NatGe...8..235B|doi=10.1038/ngeo2351|issn=1752-0908|url-access=subscription}}</ref><ref>{{Cite journal|last1=Kent|first1=Adam J. R.|last2=Darr|first2=Cristina|last3=Koleszar|first3=Alison M.|last4=Salisbury|first4=Morgan J.|last5=Cooper|first5=Kari M.|date=September 2010|title=Preferential eruption of andesitic magmas through recharge filtering|url=https://www.nature.com/articles/ngeo924|journal=Nature Geoscience|language=en|volume=3|issue=9|pages=631–636|bibcode=2010NatGe...3..631K|doi=10.1038/ngeo924|issn=1752-0908|url-access=subscription}}</ref>

This process contributes to [[global warming]] primarily through their large, continuous emissions of the [[greenhouse gas]] CO₂.<ref name="link.springer.com">{{Cite journal|last1=Giammanco|first1=Salvatore|last2=Bonfanti|first2=Pietro|date=2009-03-01|title=Cluster analysis of soil CO2 data from Mt. Etna (Italy) reveals volcanic influences on temporal and spatial patterns of degassing|url=https://link.springer.com/article/10.1007/s00445-008-0218-x|journal=Bulletin of Volcanology|language=en|volume=71|issue=2|pages=201–218|doi=10.1007/s00445-008-0218-x|issn=1432-0819|url-access=subscription}}</ref><ref name=":362">{{Cite journal|last1=Carn|first1=S. A.|last2=Bluth|first2=G. J. S.|date=December 2003|title=Prodigious sulfur dioxide emissions from Nyamuragira volcano, D.R. Congo|url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2003GL018465|journal=Geophysical Research Letters|language=en|volume=30|issue=23|page=2211|bibcode=2003GeoRL..30.2211C|doi=10.1029/2003GL018465|issn=0094-8276}}</ref> Volcanoes release significant amounts of CO₂ into the atmosphere during both their quiescence and high eruptive activity periods.<ref name=":352"/> The continuous release and accumulation of CO₂ (accounting for up to 10% of the global total budget) leads to an increase in the concentration of greenhouse gases in the atmosphere.<ref name="link.springer.com"/> This gas acts like a blanket, trapping heat that would otherwise be re-radiated into space, causing the heat to accumulate and, as a result, warming the Earth's surface. Although volcanic CO₂ emissions are relatively small compared to human-caused emissions from burning fossil fuels, the persistent degassing of volcanoes like Mt. Etna still plays a role in the [[carbon cycle]], indirectly contributing to [[climate change]] by increasing the amount of CO₂ in the atmosphere.<ref name=":362"/><ref>{{Cite journal|last1=Shinohara|first1=H.|last2=Aiuppa|first2=A.|last3=Giudice|first3=G.|last4=Gurrieri|first4=S.|last5=Liuzzo|first5=M.|date=September 2008|title=Variation of H₂O/CO₂ and CO₂/SO₂ ratios of volcanic gases discharged by continuous degassing of Mount Etna volcano, Italy|url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2007JB005185|journal=Journal of Geophysical Research: Solid Earth|language=en|volume=113|issue=B9|doi=10.1029/2007JB005185|bibcode=2008JGRB..113.9203S |issn=0148-0227}}</ref>

== See also == * {{annotated link|Cave of Dogs}} * {{annotated link|Fumarole}} * {{annotated link|Whitedamp}}

== References == {{reflist}}

[[Category:Geological hazards]] [[Category:Swahili words and phrases]] [[Category:Volcanic degassing]] [[Category:Carbon dioxide]]