Dune Fields, Namibian Coastal Desert
Namib-Naukluft National Park is an ecological preserve in Namibia’s vast Namib Desert. Coastal winds create the tallest sand dunes in the world here, with some dunes reaching 980 feet (300 meters) in height.
Brandberg Intrusion, Namibia
Rising unexpectedly from the heart of the Namib Desert in northern Namibia, the Brandberg Massif is an exhumed granite intrusion dating to some 120 million years ago. It rises to 2,606 meters (8,550 feet) and is higher than any other feature for hundreds of kilometers. Unique plant and animal communities thrive in its high-altitude environment, and prehistoric cave paintings decorate walls hidden in its steep cliffs.
Slightly south and to the west of the Brandberg is the much-eroded Messum Intrusion. Both of these intrusions reflect a period of extraordinarily widespread geological unrest in the Earth’s history, which preceded the opening of the Atlantic Ocean and the effusion of vast volumes of basaltic lavas of the Karoo formation that form the Drakensberg plateau. Karoo lavas are exposed immediately to the west of the intrusion. Rocks forced aside by the upward movement of the intrusion are visible encircling the margin of the Brandberg, tilted sharply upward. Ancient gneisses, distinguished by their lineated texture, are conspicuous along the dry river valley in the center of the frame.
The existence of a set of lavas in South America of the same age and type as those of the Karoo was used for many years by some geologists as strong evidence that Africa and South America had once been united. However, their arguments were not widely accepted until geophysical data demonstrated the reality of plate tectonics.
Sediment laden drainage, Betsiboka River, Madagascar
The Betsiboka is Madagascar’s main river, flowing for a total of 525 kilometers (326 miles) from north of Tananarive. The river is navigable for at least 130 kilometers (81 miles) inland and the lower reaches pictured here are noted for their extensive rice fields. While the red sediment being transported provides an attractive and informative example of a river estuary, it is a symptom of an ecological disaster for Madagascar. Humans have felled and cleared the island’s natural cover of tropical forest so extensively that soil erosion has been vastly accelerated. Much of the sediment visible in the river represents an irreplaceable natural asset.
Brick-red lateritic soils, the result of tropical weathering, are responsible for the strong color of the sediments. Most of the deforestation in Madagascar has taken place over the last 20 years, the same period during which observations from space have been conducted. Recent observations show that very little of the original forest remains.
Galapagos Islands, Pacific Ocean
The Galapagos Islands, which are part of Ecuador, sit in the Pacific Ocean about 1000 km (620 miles) west of South America. The islands sit on the Galapagos rift, an offshoot of the East Pacific Rise. The islands were formed by volcanic eruptions, which took place millions of years ago. The islands straddle the equator in a chain of 13 large island and many smaller ones. They lie between 1° north and 1°3′ south, and lies between 89 and 92° west longitude. With the exception Isabella, the islands have high volcanic craters at the island centers, that rise to 1,520 meters and are roughly circular in shape.
Unlike most remote islands in the Pacific, the Galapagos have gone relatively untouched by humans over the past few millennia. As a result, many unique species have continued to thrive on the islands. Over 95 percent of the islands’ reptile species and nearly three quarters of its land bird species cannot be found anywhere else in the world. Two of the more well known are the Galapagos giant tortoise and marine iguanas. The unhindered evolutionary development of the islands’ species inspired Charles Darwin to begin The Origin of Species eight years after his visit there. To preserve the unique wildlife on the islands, the Ecuadorian government made the entire archipelago a national park in 1959. Each year roughly 60,000 tourists visit these islands to experience what Darwin did over a century and a half ago.
Anticlines and salt domes, Gulf coast, Iran
One of the most spectacular examples of anticlinal fold structures lie on the north shore of the Strait of Homuz in the Persian Gulf. Located near the important city of Bandar Abbas, these folds form the foothills of the Zagros Mountains, which run north-northwesterly through Iran. The folds were formed when the Arabian shield collided with the western Asian continental mass about 4 to 10 million years ago. Subduction still continues slightly further east, beneath Baluchistan, but is inactive in the Gulf itself. Although not obvious in the photograph, the shortening expressed by the folds is accompanied by extensive thrusting on the easterly dipping planes. All the deformation is geologically young; the folded sediments are Paleogen and Neogen. Simple anticlinal structures are well know as classic traps for hydrocarbons, and some producing wells are located in the area.
The other features that are prominent in this photograph are the dark circular patches. These represent the surface expression of salt domes that have risen diapirically from the Cambrian Hormuz salt horizon through the younger sediments to reach the surface. Only in a hot arid environment such as that of the Gulf can the soluble salt escape rapid erosion. Salt domes also are frequently favorable sites for trapping hydrocarbons.