In the Needles District of Canyonlands National Park, a group of parallel valleys cut across the rust-colored surface of the Colorado Plateau. The features—grabens—are caused by blocks of rock sinking between parallel faults in the Earth. Most of the grabens are 25 to 75 meters (82 to 246 feet) deep and extend for about 25 kilometers (16 miles).
The origin of these distinctive features dates back some 300 million years, when a shallow inland sea covered the area. Salty deposits called evaporites accumulated along the bottom of the ocean basin. As more material was deposited, the evaporite layer grew to be more than a thousand meters thick in some places.
Environmental conditions gradually changed over time. During some periods, ocean levels were higher and deposited layers of limestone. When sea levels were lower and the crust was exposed to air, layers of sandstone, mudstone, and siltstone were laid down on top of the evaporites. The result was a layer-cake of rock formations that alternate between shades of red, white, gray, and brown.
About 60 million years ago, the oceanic plates in the Pacific began sliding underneath North America, pushing the Colorado Plateau upward. During this period, a network of cracks—some of which would later became the walls of the grabens—formed in weak parts of the rock.
Starting about 10 million years ago, the Colorado River started chiseling into the plateau, carving a deep canyon. When the river sliced into the evaporite layer about 55,000 years ago, the relatively soft rock began to erode. Over time, the whole rock layer became so saturated with water that it began to shift and move westward toward the river. As the evaporite layer moved, the overlying blocks of rock sank, creating the grabens. The sinking blocks also forced adjacent rock upward, forming elevated features known as horsts.
The prime example of beach evolution is the coastal barrier. These strips of land are usually long and narrow and run parallel to the mainland. Sometimes they are islands and other times they are connected to land at one end, a feature dubbed a “spit.” Scientists estimate that there are more than 2,100 barrier islands in the world fronting nearly 10 percent of continental shorelines. In the United States, barrier spits and beaches line up along nearly a quarter of the coast, mostly facing the Atlantic Ocean and Gulf of Mexico. Some of the best-known barrier systems include Padre Island in Texas, the Outer Banks of North Carolina and Virginia, the south shore of Long Island, New York, and the Sea Islands of South Carolina and Georgia.
These beaches are not only attractive to human settlers and tourists; they promote the development of critical marsh and wetland habitats. Barrier beaches also protect the mainland from the full force of ocean wind and wave energy. This is particularly important on shorelines prone to hurricanes, typhoons, and nor’easters.
Barrier beaches and spits are constantly raised up, shifted, and torn down by the natural ebb and flow of waves, currents, winds, and tides. Storms can reshape them abruptly and dramatically. Hooks form, inlets open and close, and beaches slowly march across their back bays and lagoons toward the mainland, as if seeking shelter from the full force of the ocean. This process allows them to naturally march upwards as sea levels rise.
On the southeastern elbow of Cape Cod, where the New England coast reaches out into the cold and choppy North Atlantic, this natural progression has been taking place in full view of satellites for more than 30 years. The images above were collected by three generations of Landsat instruments: the Thematic Mapper on Landsat 5, the Enhanced Thematic Mapper Plus on Landsat 7, and the Operational Land Imager on Landsat 8. Each scene shows the shape of the coast off of Chatham, Massachusetts, from June 12, 1984, through July 30, 2013. (Click on the dots to scroll through the images, or hit the play arrow for a slideshow.)
The changes to the Nauset-Monomoy barrier system are sometimes subtle and sometimes dramatic. In 1984, when the image series begins, an unbroken barrier spit shields the Atlantic-facing coast of Chatham and its harbor. South of the mainland, North and South Monomoy Islands stand apart from each other and from the coast. Over the span of 30 years and 15 images, three major breaches open in the system and the barrier islands connect to the coastline and to each other at various times. All the while, sandbars and shoals—which appear as light tan waters just offshore—hint at the underwater movement of sand up and down the coast.
The first major change appears in September 1987. A nor'easter in January 1987 cut a new inlet through North Beach, forming what the locals called South Beach Island. In the 1990 image, the north end of South Beach Island nearly connects to the mainland; by 1993, the connection is complete and the south end of the spit starts to grow longer and wider. For most of the 1990s and early 2000s, South Beach keeps reaching southward toward South Monomoy. Meanwhile, the waters around North Monomoy grow shallower as sandbars and shoals rise up toward the water line.
Swollen rivers have caused devastating flooding across the Balkan region of Europe. Heavy rain—including three months’ worth in just three days—has overwhelmed the region’s rivers, affecting more than three million people. The Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite acquired this image of the Sava River on May 23, 2014. Bosnia and Herzegovina is on the south side of the river, while Croatia is to the north.
The top image shows a close-up of the town of Vidovice, Bosnia and Herzegovina, at ALI’s full resolution. The city is surrounded by and submerged under floodwater. The lower image provides a wider view of the region. Muddy, brown water expands out from the river channel on both sides.
The floods have triggered landslides that displaced landmines and warning signs. One mine exploded in the Brcko region. The floods are expected to continue with ongoing heavy rain throughout the Balkans.
NASA Earth Observatory images by Jesse Allen and Robert Simmon, using Landsat data from the U.S. Geological Survey. Caption by Adam Voiland.
NASA Earth Observatory image by Jesse Allen, using EO-1 ALI data provided courtesy of the NASA EO-1 team. Caption by Holli Riebeek.