Today’s caption is the answer to our November 2017 puzzler.
In central Algeria, just north of the Tropic of Cancer and about 1200 kilometers (750 miles) south of the Algiers metropolis, lies a land as desolate as it is beautiful.
In this part of the Sahara, known as the Tanezrouft Basin, the land is especially parched, with annual rainfall measured in millimeters (less than 5 millimeters or 0.2 inches). This is a hyperarid place of soaring temperatures and scarce access to water or vegetation. There are no permanent residents here, only occasional Tuareg nomads. The basin’s colloquial name is the “Land of Terror” because, for many, to traverse this land is to stare death in the face.
The severe conditions that make this basin a barren expanse for life also lay bare its exquisite geology. Wind erosion—caused by constant sandblasting through millennia of frequent sandstorms—has exposed ancient folds in the Paleozoic rocks. This natural-color image, acquired on October 22, 2017, by the Operational Land Imager (OLI) on Landsat 8, shows concentric rings of exposed sandstone strata that create stunning patterns across the Tanezrouft Basin. When viewed from 705 kilometers (438 miles) above Earth, the exposed geologic features create an arresting work of abstract art.
The sandstone canyons in this region have walls that rise as high as 500 meters (1,600 feet), and salt flats can be found in their lower reaches. The flats indicate that water played a role in sculpting this landscape. “Intermittent flooding has occurred often enough to mold the landscape pretty thoroughly over millions of years,” explained P. Kyle House, a geologist with the U.S. Geological Survey.
“There are numerous canyons in this region that both follow and abruptly cut directly across the grain of the tilted and folded strata,” he added. “These patterns are striking and reminiscent of landscapes formed on folded strata in, for example, the Red Desert of southern Wyoming and even parts of the heavily forested Appalachian Mountains of the Eastern United States.”
On the ground, life is a rarity. Fifty miles east of this area, the trans-Saharan highway—known as one of the world’s most brutal roads—makes its way through the desert.
- European Space Agency (2009, October 23) Earth from Space: ‘Land of Terror.’ Accessed December 1, 2017.
- Gizmodo (2015, March 16) Erosion Exposes Curving Sedimentary Beds in the Land of Terror. Accessed December 1, 2017.
- Impossible Geology (2010, February 15) Tanezrouft ‘Land of Terror,’ Algeria. Accessed December 1, 2017.
- Petit-Make, N., et al. (1990) First evidence for Holocene rainfall in the Tanezrouft hyperdesert and its margins Palaeogeography, Palaeoclimatology, Palaeoecology 79, 333–338.
- Wikipedia (2017) Tanezrouft. Accessed December 1, 2017.
NASA Earth Observatory image by Jesse Allen, using Landsat data from the U.S. Geological Survey. Story by Laura Rocchio, Landsat science outreach team. We also tip our hats to James Varghese, the EO reader who correctly identified the location and the rock formations.