Lake Ngozi is the second largest crater lake in Africa. It can be found near Tukuyu, a small town in the highland Rungwe District, Mbeya Region, of southern Tanzania in East Africa. It is part of the Poroto Mountains and the northern rim of the caldera is the highest point in the range. The caldera mostly composed from trachytic and phonolitic lavas. Ngozi is a Holocene caldera that generated the Kitulo pumice 12,000 years ago during a Plinian eruption, most likely in the same eruption that generated the caldera. Other eruption deposits are the Ngozi Tuff and the Ituwa Surge base surge deposits of uncertain age, but intermediary to the Kitulo pumice and Ngozi Tuff. The youngest activity generated a pyroclastic flow that flowed southwards for 10 km around 1450 CE. Some pyroclastic cones surround the volcano. The walls of the caldera are forested, with the exception of segments scoured by landslides and high cliffs that inhibit access to the water. The inner caldera is forested with Maesa lanceolata, Albizia gummifera and Hagenia abyssinica, far fewer tree species than neighbouring mountains consistent with the recent geological origin of the volcano. The caldera itself is not subjected to hydrothermal activity, but large subaqueous CO2 emissions and local legends of the killing power of the lake indicate a danger of limnic eruptions. The lake floor according to echosounding is flat and has no terraces. The lake does not undergo large scale fluctuations in lake level, with only minor differences between the dry and rainy seasons. Air temperatures above the lake are around 18 °C with only minor seasonal variations. Sporadically, the forests were occupied by Safwa hunters. Reports in 2013 stated that in the following year a geothermal project would commence in the vicinity of the volcano halfway between Ngozi and the town of Mbeya.
There are a number of local myths and folk tales which surround the volcanic lake, and the surrounding area. The Nyakyusa People say that a sharman, called Lwembe, was chased from his birth village to the waters of Lake Ngozi after the people had become weary of the deceptive nature of his magic. Once Lwembe was an inhabitant of the waters edge the local tribe's cattle began to disappear; it is said that villagers started going missing too if they ventured too close to the waters. Nyakyusa elders dispelled the area by rolling a huge boulder which had been placed in the heart of a fire for three days into the water, while casting their own spells. Since that time, the evils spell on the Lake has not returned. The most commonly heard myth and folk tale is that of a group of Colonial German soldiers who disposed of treasure into the waters of the lake. They had spell on the Lake to protect the gold and hamper any other persons efforts to reclaim it. Some variations of the myth suggest that this caused an emission of poisonous gasses while others claim that there is a 12 headed snake which protects the treasure and comes out to the surface on sunny days. Whether there ever was treasure remains a mystery.
