An Earth Day present from space: Europe and Asia’s watery gateway

An Earth Day present from space: Europe and Asia’s watery gateway


Considered to be the boundary between Europe and Asia, the Bosporus (Turkish Bogazici) Strait connects the Black Sea with the Sea of Marmara in northwest Turkey. In celebration of Earth Day, NASA has released a new shaded relief and radar image of this geologically complex and historically rich region, taken by NASA’s Shuttle Radar Topography Mission in February 2000.

The image is available from NASA’s Jet Propulsion Laboratory, Pasadena, Calif., on the
JPL Planetary Photojournal at:

The Bosporus Strait is depicted in the centre of the view. The Black Sea at the top of the image and Sea of Marmara below the centre are coloured blue, along with several large lakes. The largest lake, to the lower right of the Sea of Marmara, is Iznik Lake.

The large city of Istanbul, Turkey is located on both sides of the southern end of the strait. Its stronger reflection of radar causes it to appear as a brighter (light green to white) area on the image. Istanbul is the modern name for a city with a long history, previously known as both Constantinople and Byzantium. In 330 A.D., Constantine rebuilt Istanbul on the site of an
earlier Greek city as the capital of the Roman Empire. It later served as the capital of the
Byzantine and Ottoman empires until 1922.

The narrow Gulf of Izmit extends to the east (right) from the Sea of Marmara. On August 17, 1999, a magnitude 7.4 earthquake, often called the Izmit or Kocaeli, Turkey earthquake, heavily damaged the city of Izmit at the end of the gulf and killed at least 17,000 people. A previous earthquake under the Gulf of Izmit in 1754 killed at least 2,000 people. The Izmit earthquake ruptured a long section of the North Anatolian Fault system from off the right side of this image continuing under the Gulf of Izmit. Another strand of the North Anatolian Fault system is visible as a sharp linear feature in the topography south of Iznik Lake. Surveys measuring water depth in the area show that the North Anatolian Fault system extends beneath and has formed the Sea of Marmara, in addition to the Gulf of Izmit and Iznik Lake. Scientists are studying the North Anatolian Fault system closely to determine the risk of future large earthquakes on the faults close to Istanbul.

Three visualization methods were combined to produce this image: shading and colour coding of topographic height, and radar image intensity. The shade image was derived by computing topographic slope in the northwest-southeast direction. Northwest-facing slopes appear dark and southeast-facing slopes appear bright. Colour coding is directly related to topographic height, with green at the lower elevations, rising through yellow and brown to white at the highest elevations. The shade image was combined with the radar intensity image to add detail, especially in the flat areas.