I vinterferien har vi gjort som nordmenn flest, reist til fjells. Storebror har har besøkt oss, og sammen har vi kjørt en lang tur nordover langs Usumbara Mountains til høylandet i Great Rift Valley. I masaienes land har vi besøkt den alkaliske innsjøen Lake Natron, besteget den aktive vulkanen Ol Doinyo Lengai, og besøkt Ngorongorokrateret og Mkomazi nasjonalpark.
Ol Doinyo Lengai
“Oldoinyo Lengai is a volcano in the Eastern Rift Valley, North Tanzania. Its name means ‘Mountain of God’ in the language of the Maasai people who inhabit this area. Oldoinyo Lengai is of particular interest to geologists because it is the world’s only active volcano that erupts natrocarbonatite lava. It is also the only active volcano in this part of the East African Rift Valley, though there are many older extinct volcanoes in this region. Oldoinyo Lengai rises about 2000 metres above the Rift Valley floor to a height of approximately 2886 metres.”
Lake Natron
Lake Natron is a salt or alkaline lake located in north Ngorongoro District of Arusha Region in Tanzania. It is in the Gregory Rift, which is the eastern branch of the East African Rift. The lake is within the Lake Natron Basin, a Ramsar Site wetland of international significance.
The lake is fed principally by the Southern Ewaso Ng’iro River, which rises in central Kenya, and by mineral-rich hot springs. It is quite shallow, less than three metres (9.8 ft) deep, and varies in width depending on its water level. The lake is a maximum of 57 kilometres (35 mi) long and 22 kilometres (14 mi) wide. The surrounding area receives irregular seasonal rainfall, mainly between December and May totalling 800 millimetres (31 in) per year. Temperatures at the lake are frequently above 40 °C (104 °F).
High levels of evaporation have left behind natron (sodium carbonate decahydrate) and trona (sodium sesquicarbonate dihydrate). The alkalinity of the lake can reach a pH of greater than 12. The surrounding bedrock is composed of alkaline, sodium-dominated trachyte lavas that were laid down during the Pleistocene period. The lavas have significant amounts of carbonate but very low calcium and magnesium levels. This has allowed the lake to concentrate into a caustic alkaline brine.
