NASA image reveals rare volcanic formation
South Africa's Pilanesberg National Park is known for its wildlife, but it is also home to a unique geological feature.
According to NASA, the area contains "one of the world's largest and best preserved alkaline ring dike complexes."
Ring dikes are rare structures on Earth that are formed after numerous cycles of volcanic eruptions cause magma to fill underground cracks that end up in the shape of concentric circles.
See the formation:
Last month, one of the land observing imagers on NASA's Landsat 8 satellite captured an overhead photo of the Pilanesberg rings during a time when the streams that often flow across them were dry.
Estimated to be about 15 miles wide, the formation's tallest point stretches more than 5,000 feet above sea level, with the typical hill averaging 500 to 1,000 feet higher than the lowland environment.
Scientists place the initial volcanic eruption at about 1.3 billion years ago, with the total process occurring over the course of hundreds of millions of years.