Tswaing is an

impact crater An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact crater ...

in South Africa that is accompanied by a museum. It is situated 40 km to the north-west of

Pretoria Pretoria () is South Africa's administrative capital, serving as the seat of the executive branch of government, and as the host to all foreign embassies to South Africa. Pretoria straddles the Apies River and extends eastward into the foothi ...

. This astrobleme is 1.13 km in diameter and 100 m deep and the age is estimated to be 220,000 ± 52,000 years (

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

). The impactor is believed to have been a

chondrite A chondrite is a stony (non-metallic) meteorite that has not been modified, by either melting or differentiation of the parent body. They are formed when various types of dust and small grains in the early Solar System accreted to form pr ...

stony meteorite In meteoritics, a meteorite classification system attempts to group similar meteorites and allows scientists to communicate with a standardized terminology when discussing them. Meteorites are classified according to a variety of characteristics ...

some 30 to 50 m in diameter that was vapourised during the impact event. Morokweng impact structure, another crater of

origin, lies north-west of

Vryburg Vryburg () is a large agricultural town with a population of 48,400 situated in the Dr Ruth Segomotsi Mompati District Municipality of the North West Province of South Africa. It is the seat and the industrial and agricultural heartland of the di ...

Etymology

The name ''Tswaing'' means "place of salt" in Tswana and the crater was also formerly known in English as ''Pretoria Saltpan crater'' and in Afrikaans as ''Soutpankrater''.

History

Stone tools from the

Middle Stone Age The Middle Stone Age (or MSA) was a period of African prehistory between the Early Stone Age and the Late Stone Age. It is generally considered to have begun around 280,000 years ago and ended around 50–25,000 years ago. The beginnings of ...

show that the crater was regularly visited by people from as far back as 100,000 years ago in order to hunt and collect salt. Water in the crater comes from surface springs, ground water and rain water and is rich in dissolved

carbonates A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate g ...

and

sodium chloride Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35. ...

s. Tswana and Sotho people harvested the salt by filtering and

decoction Decoction is a method of extraction by boiling herbal or plant material (which may include stems, roots, bark and rhizomes) to dissolve the chemicals of the material. It is the most common preparation method in various herbal-medicine systems. Dec ...

between 1200 and 1800. Between 1912 and 1956 brine was pumped from the floor of the crater by the company ''SA Alkali Ltd.'' in order to extract soda and salt. A scientific dispute was ongoing regarding the origin of the crater between supporters of volcanic origin (Wagner, 1922) and those who believed it is an impact crater (Rohleder, 1933) until 1990, when examination of the core from a borehole proved that it is an impact crater.

Museum

The impact crater is accompanied by a museum.

Status of protection

Tswaing is currently on the ''tentative list'' for consideration as a

World Heritage Site A World Heritage Site is a landmark or area with legal protection by an international convention administered by the United Nations Educational, Scientific and Cultural Organization (UNESCO). World Heritage Sites are designated by UNESCO for ...

References

External links