Brukkaros - A Crater caused by an Explosion - News - Gondwana Collection


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Brukkaros - A Crater caused by an Explosion

Avatar of inke inke - 19. August 2016 - Discover Namibia

Brukkaros: Not an extinct volcano.

Many believe that the enormous crater of Brukkaros west of the national road between Mariental and Keetmanshoop is an extinct volcano. Geologists initially shared this opinion because of the mountain’s external shape. It is 1,603 metres high, rising 600 metres above the plain, the diameter at its base is 10 kilometres, the diameter of the crater is 3 kilometres and the shape of the slope is typical of a volcano. But the rock types that are usually found in the vicinity of fire-spitting mountains are absent around Brukkaros. Only when geologists studied the rocks in and around the crater thoroughly was the secret of the formation of Brukkaros finally unravelled.

The crater mountain formed some 80 million years ago, at the time when the breakup of the ancient supercontinent of Gondwana was in its final stages and South America drifted away from Africa. The site where Brukkaros rises today was then below the surface of the earth. Liquid magma intruded into the earth’s crust from great depths but did not make it to the surface, as would have happened in a volcanic eruption. Instead, the upper layers of rock in the earth’s crust were lifted. The pressure from below was so enormous that a mountain with a rounded dome bulged up on the surface.

The bulging stretching surface caused fissures and cracks to form in the rock layers. The hot magma shot through these into a layer of rock containing ground water. The water was immediately superheated turning to steam. This resulted in a buildup of enormous pressure that triggered an explosion of tremendous proportions. Part of the domed surface was blasted away and the cavity under the bulge collapsed, in the process forming what is now the Brukkaros caldera.

Brukkaros differs from a volcano in that while a volcano gradually builds up on the surface as lava continuously pushes up from inside and is hurled out, Brukkaros was formed through an explosion. Water later on accumulated in the caldera. Erosion of the inner walls over time led to the lake being filled up with sediments. The magma below was still liquid and caused the formation of hot springs around the lake. The springs brought chemical solutions to the surface that eventually cemented the rubble on the crater’s floor. This type of rock, called breccia, is still found on the floor of Brukkaros.

In the course of millions of years a deep gorge was dug by water draining off the southern slope of the crater. The floor and the rim of the crater can be accessed through this gorge. This feature probably also inspired the local Nama people to call the mountain Geitsi Gubib, which means “large leather loincloth”. This traditional piece of clothing that women tied around their hips apparently had the same shape as the enormous mountain. The present name can perhaps be explained this way: broek, pronounced “brook”, is the Afrikaans word for pants, while karos is the Nama word for loincloth. 

These days a hiking trail leads through the gorge into the crater, snaking its way along the southern slope right up to the rim. The trail passes some dilapidated buildings, remnants of the Smithsonian Institution and the National Geographic Society of the USA observatory manned from 1926 until 1931. Daily measurements were taken to collect data on fluctuations in the sun’s energy because it was assumed that these influenced the weather. To enable such readings to be taken a site was needed where the loss of radiation through the atmosphere was low, where the position of the sun was high in winter and where days were predominantly cloudless throughout the seasons. The station existed from October 1926 until December 1931 and was abandoned because a connection between solar radiation and weather patterns could not be proven.

Nothing is left, however, of the heliograph station installed during German colonial times on the eastern rim of Brukkaros. The Schutztruppe (German colonial forces) established a chain of heliograph stations on mountain tops from Lüderitz via Keetmanshoop to Windhoek to send signals using mirrors or lights. A transmitter mast now stands on the crater’s northern rim.

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