Lake Bosumtwi

Lake Bosumtwi
Location	Ghana
Coordinates	6°30.3′N 1°24.5′W / 6.5050°N 1.4083°W / 6.5050; -1.4083Coordinates: 6°30.3′N 1°24.5′W / 6.5050°N 1.4083°W / 6.5050; -1.4083
Type	impact crater lake
Primary inflows	rainfall [1]
Primary outflows	none [1]
Catchment area	400 km² [1]
Basin countries	Ghana
Max. length	8.6 km (5.3 mi)
Max. width	8.1 km (5.0 mi)
Surface area	49 km² (19 mi²) [1]
Average depth	45 m (150 ft) [1]
Max. depth	81 m (265 ft) [1]
Surface elevation	150 m (490 ft)
References	[1]

Lake Bosumtwi (also spelled Bosomtwe), situated within an ancient meteorite impact crater, is approximately 8 kilometres (5.0 mi) across and the only natural lake in Ghana.^[1] It is situated about 30 km south-east of Kumasi and is a popular recreational area. There are about 30 villages near this crater lake, with a combined population of about 70,000 people.

The Ashanti consider Bosumtwi a sacred lake. According to traditional belief, the souls of the dead come here to bid farewell to the god Twi. Because of this, it is considered permissible to fish in the lake only from wooden planks. Among the fish species in the lake is the endemic cichlid Hemichromis frempongi, and the near-endemic cichlids Tilapia busumana and T. discolor.^[2][3][4]

Impact crater

The Lake Bosumtwi impact crater is 10.5 km in diameter, slightly larger than the present lake, and is estimated to be 1.07 million years old (Pleistocene period).^[5][6]

Depth of crater is approximately 380 m, but, if counted together with the depth of lake sediments - 750 m.^[7]

The crater has been partly eroded, and is situated in dense rainforest, making it difficult to study and confirm its origin by meteorite impact. Shock features such as shatter cones are largely overgrown by vegetation or covered by the lake. However, drilling of the crater's central uplift beneath the lake floor has recently provided an abundance of shocked materials for scientific study.^[6] Tektites, believed to be from this impact, are found in the neighbouring country of Ivory Coast, and related microtektites have been found in deep sea sediments west of the African continent.^[6]

Climate history

Before the asteroid hit, there was a lush rainforest filled with animals. The crater from the asteroid's impact filled with rainwater, so now there is a lake.^[8]

Periods of heavy rainfall filled the crater with water, causing the lake level to rise above the lowest points of the rim. Such periods are evidenced from fossils of fish found on hilltops. Water even flowed from the basin through an overflow channel. However, there were also times when the water level was so low that the rainforest entered the basin rendering the lake only a small pond. Such a period, according to legend and now proved by paleoclimate records, lasted until about 300 years ago (Shanahan et al. 2009). Lake Bosumtwi can be used to argue that the drought over sub-Saharan Africa and the Sahel during the late 1970s originated from that of natural variability forced by a multidecadal oscillation in the thermohaline circulation, which in turn modulates sea surface temperature in the north Atlantic. This evidence shows the drought occurred via natural origins instead of anthropogenic forcing. It has been shown that historical droughts in this region were four times drier than that of the late 1970s drought.^{[citation needed]}

Human history

The legends say that in 1648 an Ashanti hunter named Akora Bompe from the city of Asaman was chasing an injured antelope through the rainforest. Suddenly, the animal disappeared in a small pond. It was as if this body of water wanted to save the animal's life. The hunter never got the antelope, though he settled close to the water and started catching fish. This place he named “Bosomtwe”, meaning “antelope god”. This story suggests that at that time the lake level was very low. The large dead trees standing offshore in the lake also evidence this, for they are over 300 years old.

The following centuries saw several wars about the lake as both the Ashanti and the Akim clashed, each claiming the area. The Ashanti prevailed.

Each village in the lake area has its own shrine or fetish grove. With the arrival of Christianity, some of people gave up former beliefs, though many continue to seek traditional help in bad times or against diseases.

The Abrodwum Stone is held to be the spiritual centre of the lake. Here, when there is such poor fishing it is considered a bad omen, the lake people sacrifice a cow. This act is celebrated in the presence of his majesty, the Ashanti king, the Asantehene himself. In the ceremony, the cow's innards are given to the stone and the rest is thrown into the lake. The crowd rushes into the water with cutlasses and axes to take their share of the meat. This is an event very much worth seeing. However, as such an omen depends on various factors, it is hardly predictable.

There is a traditional taboo against touching the water with iron and modern boats are not considered appropriate. The padua, a wooden plank requiring considerable skill to maneuver, is the legitimate method.

There are current environmental concerns, including overfishing and inadequate farming methods. The growing population increased demand for fish. Excessive fishing led to steadily decreasing catches, forcing increased reliance on agriculture. As more and more of the hills are converted into farmland, exposing the surface to the heavy rainfalls, soil erosion becomes an ever greater problem. In addition there is the changing lake level. Many villages have been submerged several times forcing the people to move up the slopes or outside the basin. That is the origin of such double names as Pipie No.1 and Pipie No.2 (see map on http://people.freenet.de/bosomtwe).

The lake is a popular resort area with local people for swimming, fishing and boat trips.

The lakeside village of Amakom has a small hospital with a doctor residing on premise, called Lake Bosumtwi Methodist Clinic, providing emergency services by boat and 4x4 ambulance.

References

• Wolf U. Reimold, Dion Brandt, and Christian Koeberl (1998). "Detailed structural analysis of the rim of a large, complex impact crater; Bosumtwi Crater, Ghana". Geology 26 (6): 543–546. Bibcode:1998Geo....26..543R. doi:10.1130/0091-7613(1998)026<0543:DSAOTR>2.3.CO;2. 

External links

• Lake Bosomtwe Ecotourism Map and Guide (notice: "Bosomtwe" is the correct spelling according to Kumasi University)
• Lake Bosomtwe Drilling Project

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