First things first. There was no volcanic eruption in or around Lake Bunyonyi last week. There could not have been a silent volcanic eruption in or around Lake Bunyonyi. Claims by “environmental experts”, dutifully reported by The Daily Monitor and NTV Uganda, that volcanic activity caused Lake Bunyonyi’s brown discoloration last week, were both false and irresponsible. Such falsehoods have the potential to alarm residents and potential tourists.
There was no volcanic or other seismic activity in the Bunyonyi area. This was very easy to ascertain, for we have easily accessible international seismic volcano and earthquake monitoring networks. These give us real time and historical information about volcanoes and earthquakes around the world.
Two of many useful sources of this information are (1) the Global Volcanism Program (GVP) at the Smithsonian Institution, and (2) Volcano Discovery. These and other sources offer daily maps of world-wide volcanic activity, and reports about the status of every known volcanic center. They offer information about the volcanic sites in Uganda, namely, Bufumbira (probably extinct), Bunyaruguru (dormant), Elgon (probably extinct), Fort Portal (dormant), Kadam (probably extinct), Katunga (dormant), Katwe-Kikorongo (dormant), Kyatwa (probably extinct), Moroto (probably extinct), Morungole (probably extinct), Muhabura (probably extinct), Mugahinga (probably extinct), and Sabinyo (probably extinct.)
Five of the 42 currently erupting volcanoes in the world are in Africa. These are Nyamuragira in Congo, Nyiragongo in Congo, Ol Doinyo Lengai in Tanzania, Fantale in Ethiopia, and Erta Ale in Ethiopia. There is no mention of any of the minor volcanoes in Rubanda District, all of them presumed to be extinct. Of course, there is no mention of Bunyonyi.
Likewise, earthquake monitoring stations did not report anything of seismological significance in the area. Volcanic eruptions almost always occur after detectable warning activity, such as earthquakes, over days, weeks, and even years. This is especially so with volcanoes that have not erupted in centuries.
Whereas Uganda does not appear to have a volcano monitoring centre, it has a robust earthquake monitoring program under the Department of Geological Surveys. It has global earthquake monitoring stations in Entebbe, Gulu, Hoima, Jinja, Kilembe, and Mburara. We are not aware of any tremors being detected in Lake Bunyonyi area. Perhaps Dr. Fred Tugume wa Mwanaki, a geophysicist who is the Acting Commissioner for Geological Survey Department, or Grace L. Nassuna, Assistant Commissioner for Geoscience, can weigh in on this conversation and, hopefully, relieve the Bunyonyi community’s angst caused by the media reports.
Besides the absence of seismological records of volcanic activity, several residents of Bunyonyi have affirmed that the media reports were false. There was no sign of the known characteristics and effects of under-water volcanic eruptions. With few exceptions, volcanoes do not indulge in quiet behaviour. Now, consider that Bunyonyi is a relatively small lake, with a maximum length of 25 km (15.5 miles), width of 7 km (4.3 miles), and surface area of 61 square kilometers (23.5 square miles). Notwithstanding unverified claims that Bunyonyi is the second deepest lake in Africa, its known average depth is 39 meters (128 feet) or 44 meters (144 feet), depending on literature source.
A submarine volcanic eruption in such a lake of mostly medium depth would have resulted in visible and potentially disastrous consequences. The residents would have felt tremors. They did not. They would have noted severe water turbulence, with high waves, even flooding and damage to lakeside buildings. They did not.
One of the drivers of this false report was the belief that Lake Bunyonyi is a crater lake. Bunyonyi is not a crater lake. It is a freshwater lake that was formed when lava from small volcanic eruptions, probably in the Muko and Murore areas of present-day Rubanda District, dammed River Ndego and created an exceptionally beautiful lake 8,000 to 18,000 years ago. Some scholars have wondered whether the lava simply deepened an already existing lake. Be that as it may, the claim that Bunyonyi is a crater lake should be debunked and retired. By definition, a crater lake is formed in the depression (caldera or crater) that follows an explosion or collapse of the peak of a volcano. It does not form in a deep valley like Bunyonyi without preceding volcanic activity.
So, what caused the water of Lake Bunyonyi to turn yellow brown? Bunyonyi appears to have experienced the well-known “browning” or “brownification” phenomenon that has affected many lakes in the last fifty years. The phenomenon occurs when dissolved organic matter (DOM), especially dissolved organic carbon (DOC), and iron (Fe) reach a critical level in a water body at which point it absorbs ultraviolet and short wavelength visible light. The human eye then sees only the yellow and brown colours.
The major drivers of this phenomenon have been extensively studied in North America and Europe. Forests, farms, human settlements, and wetlands produce organic matter that is washed into the lakes by rainfall. Climate change, increasing temperature, increasing rainfall, afforestation (establishing new forests in areas that were not previously forested), extensive planting of coniferous forests (including patula trees), lake recovery from acid rain, increased wetland products, soil degradation through overcultivation, and waterflow modification are potential drivers of this phenomenon.
These drivers may not be necessarily at play in the tropics. Unfortunately, there is such a paucity of studies on this phenomenon in the tropics that one can only speculate on the drivers in our environment. However, local conditions and human behaviour may have caused similar processes at Bunyonyi.
The discoloration is reversible. Omugurusi Biheiga, a 92-year-old resident of Bufuka, Bunyonyi, has reported that similar browning occurred in the lake over twenty-five years ago. Hopefully someone studied the phenomenon then and published their findings. New studies at Bunyonyi should inform strategies for effective response, include changing from planting coniferous to deciduous forests; forest thinning; and improved land use and water flow management. We need integrated planning and leadership that includes forestry and agricultural experts.
The Kampala media reports that an earthquake disrupted the floor of Lake Bunyonyi have now found permanent presence on the internet. Artificial Intelligence (AI), which gathers whatever is on the internet for the convenience of the unwary reader, is erroneously presenting the falsehood as reality. It is a reminder that AI is not a substitute for a personal search for evidence-based information.
This speculation has added to the myths about that beautiful lake. Alongside the myths about Bunyonyi being a bottomless lake, about spirits that rule the lake, and about Bucuranuka Island that purportedly flipped and drowned men that had denied a woman obushera (a traditional sorghum drink), we now have an imaginary volcano that struck without a belch and retreated to the earth’s crust undetected by human science.
Such stories are perfect during harmless banter among fiction weavers. Journalists and the rest of us should insist on verification before publication. It would help if some limnologists (scientists who study inland lakes) stepped up to answer key questions about this enchanting lake, such as its real depth, and the factors that have changed its waters from their legendary clarity to desert brown.
© Muniini K. Mulera