Deep blue Red Sea reefs
This beautiful true-colour image, acquired by the Sentinel-2A satellite on 28 June 2015, features the Red Sea coral reefs off the coast of Saudi Arabia.
This vast, desolate area in the very northern corner of the Red Sea is bordered by the Hejaz Mountains to the east. The area was once criss-crossed by ancient trade routes that played a vital role in the development of many of the region's greatest civilisations.
Today, the Red Sea separates the coasts of Egypt, Sudan and Eritrea to the west from those of Saudi Arabia and Yemen to the east.
It contains some of the world's warmest and saltiest seawater. With hot sunny days and the lack of any significant rainfall, dust storms from the surrounding deserts frequently sweep across the sea. This hot dry climate causes high levels of evaporation from the sea, which leads to the Red Sea's high salinity.
It is just over 300 km across at its widest point, about 1900 km long and up to 2600 m deep. Much of the immediate shoreline is quite shallow, dotted with coral reefs along most of the coast - making excellent diving spots in many areas.
Its name derives from the colour changes in the waters. Normally, the Red Sea is an intense blue–green. Occasionally, however, extensive algae blooms form and when they die off they turn the sea a reddish-brown colour.
The Red Sea lies in a fault separating two blocks of Earth's crust - the Arabian and African plates.
Navigation in the Red Sea is difficult. The shorelines in the northern half provide some natural harbours, but the growth of coral reefs has restricted navigable channels and blocked some harbour facilities.
Shallow submarine shelves and extensive fringing reef systems rim most of the Red Sea, by far the dominant reef type found here.
The lighter blue water depicted in the image means that the water is shallower than the surrounding darker blue water.
Furthermore, water clarity is exceptional in the Red Sea because of the lack of river discharge and low rainfall. Therefore, fine sediment that typically plagues other tropical oceans, particularly after large storms, does not affect the Red Sea reefs.
View the full resolution image.