Namibia is a wonderful country to see different landscapes - from forests to deserts. One form of landscape you will not see is a natural lake district. On the 824116 km² of Namibia you only will find two natural lakes with permanent water: Otjikoto and Guinas (only 15 km away). Welcome to 50% of natural permanent lakes in Namibia.
Otjikoto is a word in the Hereo language and means "deep water" - and that's right.
The lake is a result of a collapsed sinkhole of a karst cave in the dolomites of the Damara-Orogenic-Belt. In areas with carbonate rocks sinkholes occur through dissolution of the carbonates by water. Through cracks and fractures in dolomitic rocks water percolates. Carbonic acid in the water dissolves the rock. Over 700 million years in the underground the fractures enlarge to cavities and grow into caves. And when the covering rock of the cave will be instable the structure collapse, leaving behind a circular depression - such as Otjikoto. I you had the possibility to dive you would see a conical debris mound layed on the lake bed is referred to as a sinkhole. The water of the sinkhole comes form the Otavi Mountain Land flowing to the north and presents a "window" to the groundwater flow.
The lake is part of the "Karstveld" which shows a number of sinkholes and may be traced from the Tsumeb-Grootfontein-Otavi Triangle westward through the Etosha National Park and from there northwards.
Stratigraphical Otjikoto belongs to a more than 3000 m thick carbonate platform of the Otavi Group. The carbonate platform is constructed from microbial mats. The karstification of the area was done in different phases. The first phase began 700 million years ago and lasted 100 million years. The next phases were 450-280 and 65 million years ago. The final phase was 34,000-20,000 years ago.
Lake Otjikoto is located within carbonate rocks of the Neoproterozoic Otavi Group. Neoproterozoic was an era of the Precambrian 1000 to 500 million years ago. From this time age you will find fossils of the first multi-celled animals, worm-like Trichophycus and first sponges. A hypothesis of "Snowbal Earth" posits that the Earth's surface became entirely or nearly entirely frozen at least once in Neoproterozoic.
A major event during this time was the pan-african mountain building (orogenic) which related to the formation of the supercontinent Gondwana. One part of the Damara-Orogenic-Belt is the Kaoko-Belt and this correlates with the Ribiera-Belt in Brasil - but that is an other story.
By the way how would you name this hole with water: sinkhole or doline? At the end both are holes in the earth but the ways to create the holes and the shapes are different. A sinkhole has more or less steeply sloping edges. The doline (from the origin of the word) was made by process on the surface of the rocks and the shape is more like a funnel.
You see a simple hole could have a interesting history. Now it's on you to find the answers to the following questions:
1.) The hole is impressive. But how many (metric) tons of material was dissolved and taken away? A hint at O1 will maybe help.
(Optional: how man kg per year were taken away simplified during the two big phases?)
2.) In the literature the use of sinkhole as a synonym for doline has also created some ambiguity. By the origin of the word is Otjikoto Lake a doline or sinkhole and what was the indicator for you to find it out?
3.) Otjikoto is the only "museum" in Africa for what?
4.) The form of the lake is rather like an upside-down mushroom with overhangs. Johannes Stephanus Cook had a painful experience and drowned (VERDRINK) 1927. At which date (day and month)? O2 will help.
Please send your answer with your nickname preferably to: firstname.lastname@example.org (optional)
Mails via my profil are also possible but need longer time for checking.
It would be also nice to post a photo of you and the lake in the log (optional, not mandatory).
Observe that Otjikoto Lake is a National Monument - please respect the place.
To visit Ojikoto Lake you have to respect the opening times (8 am - 6 pm, 5 pm winter) and to pay for a permit at the entrance (around N$ 35 - updates are welcome). Be careful at the edge of the lake!