Risk assessment of volcanic lakes

Caldera lakes of active volcanos are sometimes a risk for the region and the assessment of danger from an eruption has to be an elementary part of the risk analyses. Since the lake Nyos CO2 eruption in Cameroon at 1986, which caused 2000 victims, the risk of a limnological CO2 eruption is known publicly, however, there are still deficits in risk assessment, particularly with respect to accumulation processes from CO2 in water bodies as well as limnological processes. Up to now circa 20 crater lakes are known in which CO2 accumulation happens and in the past eruptional gas emissions occurred several times. The relevance of the risk has increased significantly because the endangered areas are inhabited today. Yet, many crater lakes particularly in the states of South and Central America are still not or rather sufficiently investigated concerning their CO2 accumulation. At an interdisciplinary research project two deep caldera lakes, the lagoon Quilotoa near Latacunga and lake Cuicocha in the north of Quito in Ecuador were investigated to understand the mechanism of CO2 accumulation and the possible transformation in the water column.

In both caldera lakes volcanic gases and an accumulation in the lake lead to an emission of CO2. High accumulations occurred in Quilotoa, but continued access and more investigations were not possible because of the local security situation. At the caldera of Quilotoa a large amountof CO2 is released  and at windless periods a danger for people inside the caldera cannot be ruled out.

At lake Cuicocha, a wide limnological, geological, and volcanological regional survey was performed, which enables an extended risk assessment of the Cuicocha volcano.

• The Cotacachi/Cuicocha complex is an active volcano, which had two active phases according to geological investigations. One at the Pleistocene with the formation of the abundant volcanic cone Cotacachi and a recent phase with eruptions between 2500 B.C. till 700 AD. Today’s volcanic activities are emissions of volcanic gases and rising hydrothermal water.
• The CO2 emissions at the lake lead to an obvious, but not dangerous accumulation of CO2 in the water, because of constant degasification over the monomictic hydrology behaviour at the lake. Hence, a limnic eruption of CO2 is currently ruled out. 

References

• Gunkel, G., Beulker, C., Grupe, B. & Viteri, F. (2009) Survey and assessment of post volcanic activities of a young caldera lake, Lake Cuicocha, Ecuador. Natural Hazards and Earth System Science 9, 699-712.
• Gunkel, G. & Beulker C. (2009) Limnology of the crater Lake Cuicocha, Ecuador, a cold water tropical lake. Int. Rev. Hydrobiol. 94, 103-125.
• Gunkel, G., Beulker, C., Grupe, B. & Viteri, F. (2008) Hazards of Volcanic Lakes: Analysis of Lakes Quilotoa and Cuicocha, Ecuador. In: P. Fabian & P. Lagos. The role of Geophysics in Natural Disaster Prevention. Advances in Geosciences, Proceedings 14, 29-33.