Viewing page 11 of 105

This transcription has been completed. Contact us with corrections.

T45
Atlas pg. 37, 38

Southeast African Plateau
Gold, platinum, coal, and diamond mines; Vredefort impact structure

Significance: The plateau of South Africa is one of the most geologically interesting areas of the world, both for scientific and economic reasons. Some of the Earth's oldest rocks, dated at almost four billion years, lie in the southeast corner of the site on the Swaziland border. More importantly for the economy of South Africa are the gold mines which supply much of the world's gold. These are aligned along prominent east-west ridges known as the Witwatersrand (meaning "white waters ridge," from waterfalls cascading down the white quartzite faces of the gold-bearing rocks). Crushed waste rock from the mines ("mine dumps") can be seen from low Earth orbit as rectangular, buff-colored patches. The gold-bearing rocks are 2.8 billion years old and appear to be great pebbly fans laid down by rivers near an ancient coastline. Johannesburg is the center of a 200 km-long string of gold mining towns stretched along the Witwatersrand, wit ha growing population of six million people. 

Just north of the Witwatersrand lies an enormous area of volcanic rocks which contain very large quantities of platinum, much iron ore, chrome and other minerals regarded by the U.S. as strategic. Mine dumps around the platinum mines can also be seen plainly from orbit. Two billion year-old rocks, giving the earliest sure evidence for Earth's oxygen-rich atmosphere, crop out in the area. Immediately south of the Witwatersrand, the prominent rings of the 60 km-diameter Vredefort impact structure, are visible from orbit. A well-defined 60 km wide inner ring is partially surrounded by a 140 km wide ring arc. Dated at about 1970 million years ago, Vredefort is the oldest impact structure known on Earth.

Very large quantities of coal are buried in rocks (only 250 million years old) east of Johannesburg. These form the basis of South Africa's power generation capability. South Africa has been a leader in gasoline-from-coal technology for many years, to counter threats of oil sanctions. Overlaying the coal-bearing rocks are one of the Earth's greatest outpourings of volcanic lava, thousands of meters thick: they form the great cliffs of the Drakensberg (Dragons Mountains) escarpment (up to 1550 meters high--5000 feet), "the most spectacular landform in Africa." Numerous diamond "pipes," vertical chimneys of blue, volcanic rock up to one kilometer in diameter, have been punched upwards through the older rocks. Diamonds discovered in 1866 at Kimberley on the west side of the site yielded at the largest diamond then known (divided into three parts of the British crown jewels). Several diamond mines now operate on the plateau.

Physical Characteristics: The Plateau has one of the most pleasant climates in the world: at 1250-2000 meters altitude (4000-6000 feet), summers are less hot and less humid than Houston's. Snow at the latitude of the Tropic of Capricorn is very rare. Although yearly rainfall reaches as high as 120 mm (30"), droughts appear to occur cyclically every 8-11 years. Water pumped west from coastal rivers up onto the Plateau, supplements local lakes in supplying the Witwatersrand. Manufacturing and service industries have outstripped mining as well as producers of wealth and jobs. As a youth forty years ago, President Banda of Malawi walked 1600 km to seek work in Johannesburg.

Observation Techniques: Concentrate on 250 mm vertical and oblique views. Shots immediately south of track will capture the Great Escarpment (Drakensberg). Obliques with the 100 mm and 50 mm lenses are also of interest. Different views are requested. We specifically request stereoscopic photography of Lesotho, the site of a large construction project of dams, reservoirs, canals, and tunnels.

Center Point: 25.5°S, 28°E