Engare Sero Geosite is in Engare Sero village just south of the Tanzania-Kenya border between the southern tip of Lake Natron, the Rift Valley Wall, and the impressive Oldonyo Lengai. The village is about 90 km from Mto wa Mbu ward. Since becoming an official village in 2000, the town center, as well as the population, has grown tremendously. The Engare Sero Geosite is rich of several potential geo-tourism sites which if well managed might improve the livelihood and standard of living of people residing the area. In addition to that, the income of the country is expected to rise if further investment in the area to develop these geo-tourism attractions. The income of the people and country at large might be accrued from tourists’ fees and money paid for the services for instance hotels, campsite, car hire etc.
Oldonyo Lengai Mountain
“Mountain of God” or “Holy Mountain” in Maasai language is the youngest and still active volcano located in the Eastern Africa major Rift Valley, 16 km south of Lake Natron, Arusha region (Plate 48). Oldonyo Lengai is a massive Mountain 2960 m high but is not a rock. The whole area is hard packed dirt with small lose rocks stuck in. It is the first of the volcanic system of the EARV, uniquely and strangest produces natrocarbonatite lava that contains almost no silcon. The lava of Oldonyo Lengai is a carbonatite rich in the rare sodium and potassium carbonates, nyerereite and gregoryite. Nyerereite is a very rare sodium calcium carbonate mineral (Na2Ca(CO3)2) which is not stable in contact with atmosphere. J. B Dawnson named it from Oldonyo Lengai carbonatite lava in 1963 in honor of the first President of Tanzania (see Dawson 2008). Due to this unusual composition, the natrocarbonatite lava erupts at relatively low temperature of approximately 510 º C compared to over 2000 º C of basaltic lavas. This temperature is so low that the molten lava appears black like dirt black oil in sunlight rather than having red glow, common to most lava. Natrocarbonatite is also the most fluid lava in the world, with a low gas content that can flow like a white water stream. In many weather the lava on surface turns white immediately. Moreover, the lava changes physically and chemically when comes in contact with water or atmosphere.
Plate 48: The Oldonyo Lengai Mountain and its landscape
The Mountain has the eruptive history since the 19th Century to Current. The first eruptive activity was recorded in 1883-1915. Then followed that of 1917, 1926, 1940, 1950s (1954, 1955, 1958), 1960s (1966-1967), 2003-2004, 2007 where daily earth tremors were experienced from 14-07 to 18-07 then volcano erupted on 04-09-2007. Also in 2008 and recently 2010 two lava flows were photographed in an over flight. In 2010 the diameter of the crater rim ranged from 270-310 m and depth of about 110-122 m.
Evolution of Oldonyo Lengai Mountain
There were series of faulting activities on the western slopes of Gelai Mountains during lower Pleistocene time (2.58-0.78 ma) accompanied by highly gaseous volcanic activities which gave the rise to explosive craters, tuff rings and tuff cones. The NNW-SSE faulting on the lower northeastern slopes of Kerimasi was accompanied by the formation of Mica-augite tuff rings of explosion craters, such as swallow of Loluni craters and some other craters exposed in the Sinya Landare. The craters in the Sinya Landare were then eroded, the early drainage cutting through them in a W-E direction. It was on this eroded, pitted land surface that the first yellow aggromerates of Oldonyo Lengai ejected blanketing and burying the cones and craters and piling up against the Rift escarpment to its west. The faults were probably formed 1.2 ma (Dawson, 2008)and volcanic activities in the area occurred both before and after this faulting. Among the older volcanoes in the area include Ngorongoro, Ketumbeine, Gelai, Shombole, Mosonik and Kerimasi.
Oldoinyo Lengai is less than 370, 000 years old and is the strangest and youngest big volcano in this part of the Rift Valley. It was formed by complex sequence of events including explosive eruptions of tuffs and aggromerates and effusive eruption of lava. It has a steep conical volcano built up by many layers of hardened lava, tephra, pumice and volcanic ashes.
Early/ Anatomically Modern Human Footprint Assemblage
Footprint assemblages provide us with unique information about the behavior and anatomy of our extinct relatives. Oldest substantial assemblage of early modern human footprints, dating to c.120, 000 years ago were recovered at Engare Sero, Tanzania, on the southern shore of Lake Natron (Richmond et al., 2011; Plate 49-51). Richmond et.al(2011)have conducted a research at Engare Sero to uncover these footprint assemblages. According to their findings, to over 350 hominin footprints, formed in a wet volcanic ash that subsequently lithified, in an area of approximately 150m2 near the shore of paleo-Lake Natron have been uncovered. There are also trail prints of animals are present. The footprint assemblage consists of trails and a few isolated prints made by several dozen human individuals. The footprint shapes suggest that the Engare Sero prints represent anatomically modern feet and gait. Several trails head in an easterly direction with stride lengths indicating that some of the individuals were running. The majority of the trails head in the opposite direction with stride lengths consistent with a walking speed and with similar preservation, suggesting that the prints were made within a relatively short time period. The diversity of footprint sizes (heel-hallux length range: 14.5–29cm) indicates that they represent individuals ranging from adult males and females to children. The Engare Sero print assemblage provides a snapshot, potentially including information about group composition, of what could be a traveling group of early modern humans 120,000 years ago.
Plate 49: The Anatomically Modern Human footprint of Engare Sero fenced
Plate 50: A small portion of hominin footprints assemblage
Plate 51: Recent exposed animal footprints