The Ol Doinyo Lengai Route begins in Karatu/ at Mto wa Mbu junction to Engaruka and heads north along the Gregory Rift Valley to the shore of Lake Natron. The route offers amazing views of the rift escarpment, as well as stops at several unusual volcanic features called maars and tufa towers. Two archaeological sites and a refreshing waterfall are also located along the Ol Doinyo Lengai Route.
Along the way you will observe different features created by the Gregory rift valley, a branch of East African Rift System. At Engaruka, you will visit an ancient village of Engaruka “Engaruka ruins” which believed to exist between 1400 – 1800 AD. The Tufa towers, which standing at the height of 2 to 3m on the Engaruka basin, is amazing geosite not to miss. About 200 unique geological features, including maars, tuff rings and different cones type make this route interesting. You will pass on the foot of the Ol Doinyo Lengai Mt. The long trip will end up at Engaresero footprint where over 400 human footprints discovered on the volcanic ash. The footprints believed to have ages between 5,700 to 19,000 years old.
The East African Rift is a giant tear in the African continental crust and marks the point where easternmost Africa is slowly moving away from mainland Africa. The rift stretches from Ethiopia in the north to Mozambique in the south. In northern Tanzania, the rift splits into two branches, or arms, that lie on either side of Lake Victoria. This stop is located along the eastern branch of the rift, which is known as the Gregory Rift.
The eastern edge of the Gregory Rift is hardly noticeable geographically and lies somewhere to the east of Mt. Kilimanjaro. In contrast, the western edge of the Gregory Rift is marked by a steep, very high escarpment that was formed by repeated faulting over the last several million years.
The escarpment is very prominent as you look both north and south. The flat-lying layers visible in the escarpment are lava flows formed by repeated eruptions of Ngorongoro Volcano.
To the northeast lies Kitumbein Volcano, a large, nearly-circular basaltic shield volcano formed within the floor of the Gregory Rift. It rises nearly 2000 meters (6561 feet) from the rift floor and reaches an elevation of 2,942 meters (9,652 feet).
There is a poorly developed crater at the top. Kitumbein is similar in age to the Ngorongoro Highlands and is considered to be extinct.
These remarkable geologic features that look like fossilized trees are, in fact, something called tufa towers. Tufa is a porous rock made up of the mineral calcite (calcium carbonate). The formation of tufa towers requires a unique set of geologic circum-stances. First, the area must be covered with saline lake water. Second, fresh water springs must be present beneath the lake.
The fresh spring water interacts with the saline lake water and leads to the precipitation of calcite. When the calcite precipitates, it does so in the form of a hollow tube, much like a drinking straw. These tubes grow upwards to form a complicated network of hollow branches that form the odd-shaped tufa towers.
If and when the lake level drops, the tufa towers become exposed on the land surface. It is known that nearby Lake Engaruka was once much larger and extended into this area. Given the requirements for the formation of tufa towers, there is little doubt that this region was at one time covered by ancient Lake Engaruka. Based on nearby archaeological sites that are known to have been located along the lake shore, the age of the tufa towers can be roughly estimated at around 5,000 years old.
The Engaruka ruins are one of the most important iron-age archaeological sites in eastern Africa, with an origin that dates back to the 15th century. The ruins were first discovered in 1883 by a German scientist named Gustav Fisher, who likened them to tumbled-down walls of ancient castles.
They are famous for their sophisticated irrigation and cultivation system, which included canals lined by stone blocks that channelled water from the rift escarpment to multiple stone-lined cultivation terraces. The major crop was sorghum. Scientists have been able to confirm that Engaruka once had seven villages and an irrigation system that supported 20 square kilometres of farmland. In the mid-18th century, the area was suddenly abandoned, possibly due to reduced river flow and/or conflicts with other tribes.
The inhabitants were most likely ancestors of the present day Iraqw people, who practice similarly complex irrigation techniques today.
This large crater is another example of a maar. It is smaller than the Engaraku Empakaai Crater observed at Stop 56, but permits one to get a better idea of the features of a maar. The maar has steep crater walls and a fairly flat floor. The crater formed when an eruption blew out the near-surface rocks. The flat floor is comprised of fine-grained volcanic debris that settled back into the crater. The locals refer to this crater as “Shimo la Mungu” which means “Pit of God.”
This is the first stop in an area commonly referred to as the “Engaruka-Lake Natron Monogenetic Crater Field.” The field is roughly 2,500 km2 ((965 square miles) in area and contains over 200 volcanic maars, tuff cones, tuff rings, scoria cones and spatter cones. Each one of these features is the result of a single (monogenetic) volcanic eruption.
The geologic feature at this stop is a maar – a volcanic crater created by a highly explosive phreatomagmatic eruption that ejected a mixture of steam and fragmented magma. The crater extends down into the underlying rock layers and is surrounded by a ring of ejected debris. The ejected ring of this maar is much thicker on the north side, suggesting that the prevailing wind direction at the time was from south to north.
Maars are usually formed when ascending magma encounters groundwater near the surface. The water vaporizes and mixes with the slightly different origin, wherein the ascending magma itself was very rich in dissolved water (H2O) and carbon dioxide (CO2). At some point as the magma neared the surface, the H20 and CO2 rapidly exsolved (bubbled off) from the magma, creating the explosive eruption.
The Saitoti River is a major source of fresh water for the local population near Lake Natron. It has its beginnings high up on the northern slopes of Empakaai Volcano, after which it flows down a winding, steep-walled canyon before eventually emptying into salty Lake Natron. A little more than 3 km up the canyon is Engaresero Waterfall, a remarkable, natural rock amphitheatre with numerous springs flowing out of its walls creating waterfalls that cascade into the river below.
A constant spray of cool water falls into a pool, which is perfect for swimming. The hike up the river takes around 45 minutes. At many points the trail crosses the river so wearing sturdy footwear that can get wet is essential. The presence of this oasis in what is otherwise an extremely arid region is quite a sight to see and experience.
This stop provides a wonderful view of Oldoinyo Lengai, which is located just north of the Geopark’s northeastern border. Ol Doinyo Lengai means “Mountain of God” in the Maasai language and it is sacred to the Maasai peoples. It is an active stratovolcano with an elevation of 2,962 meters (9718 feet). It is the only active volcano in Tanzania and one of a select few that are still active in the East African Rift Zone. The volcano has erupted many times since it first began to be observed by geologists. Major eruptions have occurred in 1880, 1914-15, 1926, 1940-41, 1958, 1960-66, 1983-93, 1994-98, 2007-8 and most recently, 2013. Several small earthquakes were reported by nearby residents during the 2013 eruption.
Ol Doinyo Lengai is unique among all active volcanoes on earth in that it often erupts lavas that consist primarily of sodium carbonate, otherwise known as carbonatite. All other volcanoes erupt lavas that are rich in silica. Due to this unusual composition, the lava erupts at fairly low temperatures of approximately 510 °C (950 °F).
This temperature is so low that the molten lava appears black in sunlight, rather than having the red glow common to most lavas. The sodium and potassium carbonate minerals that make up the lavas are unstable at the Earth’s surface and quickly turn from black to light grey to even white in colour.
Some of these light-coloured lavas can be seen near the summit. Interestingly, when the first European map makers worked in central East Africa, they identified three mountains topped by snow: Mt. Kilimanjaro, Mt. Kenya and Oldoinyo Lengai. We now know that the “snow” on Oldoinyo Lengai is actually the light-coloured carbonatite lava.
Other carbonatite volcanoes exist in the world although none are active. The Fen volcanic province in Norway’s Gea Norvegica UNESCO Global Geopark contains the remains of a carbonatite volcano that was active over 580 million years ago.
Located along the southern shore of Lake Natron, the Engaresero Footprints site contains the largest assemblage of early human footprints in Africa. Over 400 modern human (Homo sapiens) footprints, as well as tracks of zebra and various bovid, can be found in an area the size of a tennis court.
The footprints are preserved in an ancient volcanic mudflow that originated from nearby Oldoinyo Lengai Volcano. The large, pentagonal features also seen on the ground are desiccation (drying) cracks that occurred as the mudflow cooled down and dried out. The age of the footprints has been placed at somewhere between 5,700 and 19,000 years old.
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