The most obvious ocean boundary is between land and sea. From whatever vantage point land, sea, air, or space coastlines encompass such a variety of forms that they have always intrigued the viewer. From space, the shores of the ocean offer scenes and provide information not available to earthbound investigators. It is fortunate, therefore, that astronauts have taken the opportunity to acquire many photographs of the land-sea boundary.
Nile Delta Mississppi
Po Delta Betsiboka
Nimrod Sound Strait of Dover Southern
There are some 440,000 kilometers of coastline around the land masses of the world. In 1980, the United Nations estimated that two thirds of the world's population lived within a few kilometers of the sea. Though such a percentage may at first boggle the mind, it is probably a signiflcant decrease from the coastal populations in all the preceding millennia of human history.
With the growth of transportation, communications, engineering, and modern agricultural practices, many inland areas can support habitation that was impossible only a few decades ago. Consider, furthermore, the fact that tens of thousands of kilometers of coastline are not habitable, such as those in Antarctica, Tierra del Fuego, Greenland, and the Arctic coasts of Canada and Siberia. For most of human history, much of the population has crowded the world's coasts.
Coasts come in an uncountable variety of shapes (Guilcher, 1958). They have vistas and forms that have stirred the emotions and piqued the interest of humans from the earliest times: the stately White Cliffs of Dover; the awe-inspiring grandeur of the fjords of Norway, Chile, and New Zealand; the brilliant heights of the Cote d'Azur; the muddy marshes of the Mississippi, the Irawaddy, and the Yangtse; the dunes of the Red Sea, Brazil, and the Diamond Coast of southwest Africa; and the coral sands of Tahiti, the Bahamas, Tarawa, Waikiki, and Funafuti.
About half of the world's coastline has cliffs. To those who live along the coastal plains of the Gulf of Mexico or Bangladesh, or beside the North Sea shores of Germany and the Netherlands, coastal cliffs may be difficult to imagine. On the other hand, the inhabitants of Scotland, Norway, Italy, New Zealand, and Alaska might wonder, "What other kinds of coasts are there?"
As spectacular as the great sea cliffs seem, from space they cannot compare with the splendor of the estuaries, lagoons, and deltas that grace the shores of the world. All are coasts of deposition, where the land is winning from the sea, in contrast to the cliffed coasts, where soil is not deposited. And, what names they have. What histories, adventure, and intrigue they bring to mind. The Sivash, or Putrid Sea, lying on the shores of the Crimea, echoes the thundering hooves of the Light Brigade. The Nile, with its classic delta shape, suggests the aura of Anthony and Cleopatra.
Around theworld, these coastal depositional features present themselves in an endless parade of shapes, colors, and sizes. The Ganges, the Yangtse, the red Rio de la Plata, Cook's Botany Bay, the braided Betsiboka estuary, cuspate bars in Lagoa de Patos, and the Po Delta, expanding its sands to protect that pearl of all cities, Venice. Each of these impressive coasts has its place in history, each spells adventure, and each has been created in the last 6,000 years.