Affected both by terrestrial factors like agriculture, deforestation, and erosion, and by marine factors like salinity levels, ocean temperature and water pollution, coastal environments are the dynamic interface between land and sea. In this NASA image from January 15, 2002, the Gulf of Mexico is awash in a mixture of phytoplankton and sediment. Tan-colored sediment is flowing into the Gulf from the Mississippi River, whose floodplain cuts a pale, wide swath to the right of center in the image, and also from numerous smaller rivers along the Louisiana coast.
Mixing with the sediment are the multi-colored blue and green swirls that reveal the presence of large populations of marine plants called phytoplankton. Phytoplankton populations bloom and then fade, and these cycles affect fish and mammals-including humans, higher up the food chain. Certain phytoplankton are toxic to both fish and humans, and coastal health departments must monitor ecosystems carefully, often restricting fishing or harvesting of shellfish until the algal blooms have subsided.
Florida, October 14, 1999—the aftermath of Hurricane Irene in Florida in 1999 shows the dumping of sediment-laden runoff water into the Atlantic Ocean. These are huge events which can easily be seen from space. Here, sediment-filled rivers are dumping tremendous amounts of suspended sediment runoff and river flow into the Atlantic Ocean. The same thing occurred all along the Atlantic coast for hundreds of miles north—you can see how the Atlantic water currents are moving the sediment north after it enters the ocean.
The sediment being dumped into the oceans has an effect on the ecology of the oceans, both in a good and bad way. Also, this is one of the ways that the oceans have become what they are: salty.
Why is the ocean salty? Rivers discharge mineral-rich water to the oceans
Satellite view of La Plata River, South America, discharging to the Atlantic Ocean. One way minerals and salts are deposited into the oceans is from outflow from rivers, which drain the landscape, thus causing the oceans to be salty. The rain that falls on the land contains some dissolved carbon dioxide from the surrounding air. This causes the rainwater to be slightly acidic due to carbonic acid. The rain physically erodes the rock and the acids chemically break down the rocks and carries salts and minerals along in a dissolved state as ions. The ions in the runoff are carried to the streams and rivers and then to the ocean.
Here is a satellite image of Iceland in the late summer, showing ice-free landscape except for permanent ice fields. Even in summer the large permanent ice caps stand out brightly against the volcanic rock surrounding them. The brightly colored lakes and coastal waters are the result of very fine and highly reflective sediment that is ground into bits by the immense weight of glaciers and washed out to sea with glacial runoff (at the bottom of picture).
Satellite image of Iceland in the middle of winter, showing that the island country is almost completely covered in white snow and ice, obscuring the permanent glaciers and icecaps that exist year-round. Over millennia, ice has carved out deep fjords leaving fringes of land that extend like fingers into the ocean, as seen in the northwestern coast.
Also of interest are the brown swirls off the southern coast—a dust storm! Much of Iceland is bare soil that is unprotected from the ravages of atmospheric and hydrologic erosion. Along with the dust over the ocean, other areas of the Atlantic Ocean appear greenish, indicating a mixture of sediment and marine organisms called phytoplankton.
If you ever wondered if the expression "Water makes the desert bloom" was true, there is no better proof than this satellite picture by NASA of the Nile Valley in Egypt. For thousands of years, the lower Nile valley (northern end) has been a cradle of civilization. Surrounded by deserts, the Nile river brings much-needed water to the land and people, making the valley into an oasis of agriculture and life.
In this picture the Nile River runs north to the edge of the Mediterranean Sea, where it widens out into a vast delta. Just at the apex of the delta is the ancient city of Cairo. The city appears as a gray spot sandwiched between the delta and the northern end of the Eastern Desert. The leaf-shaped patch of green branching off of the left (western) side of the Nile Valley is a depression in the Libyan Desert that has been used as an irrigated agricultural area since 1800 BC, when the original irrigation canals were dug. The depression is fertilized by the Nile's water and silt.
Cumulonimbus clouds over Africa can reach a height of 12 miles (20 kilometers). Drier air causes the anvil shape.
This picture shows cumulonimbus clouds over Africa photographed from the International Space Station. Cumulonimbus (from the Latin for "puffy" and "dark") clouds form due to vigorous movement of warm and moist unstable air. Rising air currents containing water vapor and varying layers of differing-temperature air in the upper atmosphere result in these dramatic cloud formations.
Cumulonimbus Cloud over Africa is featured in this image photographed by an Expedition 16 crewmember on the International Space Station. Surface air warmed by the sun-heated ground surface rises, and if sufficient atmospheric moisture is present, water droplets will condense as the air mass encounters cooler air at higher altitudes. The air mass itself also expands and cools as it rises due to decreasing atmospheric pressure, a process known as adiabatic cooling. This type of convection is common in tropical latitudes (as in this picture) year-round and during the summer season at higher latitudes. As water in the rising air mass condenses and changes from a gaseous to a liquid state, it releases energy to its surroundings, further heating the surrounding air and leading to more convection and rising of the cloud mass to higher altitudes. This leads to the characteristic vertical "towers" associated with cumulonimbus clouds, an excellent example of which is visible in this image.
If enough moisture is present to condense and continue heating the cloud mass through several convective cycles, a tower can rise to altitudes of approximately 10 kilometers at high latitudes to 20 kilometers in the tropics -- before encountering a region of the atmosphere known as the tropopause. The tropopause is characterized by a strong temperature inversion where the atmosphere is dryer and no longer cools with altitude. This halts further vertical motion of the cloud mass, and causes flattening and spreading of the cloud tops into an anvil-shaped cloud as illustrated by this oblique photograph. The view direction is at an angle from the vertical, rather than straight "down" towards the Earth's surface. The image, photographed while the International Space Station was passing over western Africa near the Senegal-Mali border, shows a fully-formed anvil cloud with numerous smaller cumulonimbus towers rising near it. The high energetics of these storm systems typically make them hazardous due to associated heavy precipitation, lightning, high wind speeds and possible tornadoes.
Less than 80 years ago, the mighty Colorado River flowed unhindered from northern Colorado through the Grand Canyon, Arizona, and Mexico before pouring into the Gulf of California. But as this NASA Earth Observatory satellite photo from September 2000 shows, irrigation and urban water needs now prevent the river from reaching its final destination. Rather, the Colorado River just disappears into the desert sands.
The Colorado River can be seen in dark blue at the topmost central part of this image. The river comes to an end just south of the multicolored patchwork of farmlands in the northwestern corner of the image and then fans out at the base of the Sierra de Juarez Mountains. Only about 10 percent of all the water that flows into the Colorado River makes it into Mexico and most of that is used by the Mexican people for farming.
This photo shows the Ganges and Brahmaputra rivers flowing through Bangladesh. The smaller tributaries merge and converge to form the largest intertidal delta in the world. The rivers and their tributaries deposit massive amounts of silt and clay that create a maze of waterways and islands in the Bay of Bengal, as seen in this satellite image.
Credit: Image Science & Analysis Laboratory, NASA Johnson Space Center