Monday, January 13, 2014

Namibia's deep blue - Lake Otjikoto

Surrounded by legend and folklore are Namibia’s two ‘bottomless’ lakes – Otjikoto, distinguished by it emerald-green waters, and Guinas, by its mystical inky-blue depths. Both lakes lie north-west of Tsumeb – Otjikoto 24 kilometres along the road and Guinas on a farm 32 kilometres further west. Lake Guinas is therefore less accessible, and can be viewed only after obtaining the farmer’s permission.

 Lake Otjikoto was discovered by the two explorers Galton and Andersson in 1851. At the time they measured its depth as 55 metres, an assessment that was proved accurate by subsequent plumbings (the depth varying from 33–90 metres). At 100 metres, Guinas is somewhat deeper. However, the legend that Otjikoto was bottomless persisted. It was possibly this notion that led to the dumping of a considerable supply of artillery and ammunition into its murky depths by retreating Schutztruppe, rather than let the armaments fall into the hands of the South African troops. Many years later, in co-operation with the Windhoek State Museum, divers salvaged some of the equipment, among others an ammunition wagon still in perfect condition, which can be viewed in the Alte Feste Museum in Windhoek, and canons and other armaments that were restored and are now displayed in the Tsumeb Museum.

 One of the many legends that surround Lake Otjikoto is that the body of Johannes Cook, a postmaster of Tsumeb who drowned there in 1927, was never found because the lake was bottomless. In fact, because Otjikoto is shaped rather like an upside-down mushroom, it is thought that his body was caught under one of the overhangs.

Both these lakes lie in the Otavi mountain-land, which consists of a thick succession of well-stratified dolomite and limestone about 700 million years old. Being carbonates of calcium and magnesium, these rocks are soluble in water, especially if they contain some carbon dioxide. The rocks are criss-crossed by a system of solution channels that have generally developed on joints, fracture zones or bedding planes, which become partially filled with groundwater. Now and then big cavities are exposed by weathering, or the roof caves in when it becomes very thin, as in the case of Otjikoto and Guinas. These solution channels lead away from them, although the two lakes need not necessarily be directly connected. The lakes are fed by water seeping through porous rock from southern Owambo.

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