earth

by National Aeronautics

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  Tidal Flats and Channels

  Bahamas

  The islands of the Bahamas are situated on large depositional platforms—the Great and Little Bahama Banks—composed mainly of carbonate sediments ringed by reefs. The islands are the only parts of the platform currently exposed above sea level. The sediments were formed mostly from the skeletal remains of organisms settling to the sea floor; over geologic time, these sediments consolidated to form carbonate sedimentary rocks such as limestone.

  This November 2010 photograph from the International Space Station provides a view of tidal flats and underwater channels along the eastern margin of the Great Bahama Bank. The continuously exposed parts of the islands are brown, a result of soil formation and vegetation growth. To the north and west, we can see through shal ow water to the off-white tidal flats composed of carbonate sediments. The tidal flow of seawater is concentrated through gaps in the seafloor, leading to the formation of relatively deep channels that cut into the sediments.

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  The Blooming Baltic

  Baltic Sea

  Cyanobacteria are an ancient type of marine bacteria that, like other phytoplankton, capture and store solar energy through photosynthesis. Some cyanobacteria are toxic to humans and animals. Moreover, large blooms can sometimes cause oxygen-depleted dead zones where other organisms cannot survive.

  In August 2015, Landsat 8 captured this false-color view of a large bloom of cyanobacteria swirling in the Baltic Sea. Blooms flourish here during summertime, when there is ample sunlight and high levels of nutrients. Tracks of several ships show up as dark lines where they have cut through the bloom.

  Agricultural and industrial runoff from Europe can contribute to excess nutrients in the Baltic Sea. Nutrient loads have been decreasing since 1980, and coastal areas have seen improvement, yet concentrations in the open sea have not changed much.

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  Waves Beneath the Waves

  Trinidad

  Internal waves are the surface manifestation of slow waves that move tens of meters beneath the sea surface. These waves beneath the waves produce enough of an effect on the sea surface to be visible from space when they are enhanced by the reflection of sunlight, or sunglint, back toward a camera.

  This January 2013 photograph from the International Space Station shows at least three sets of internal waves interacting. The most prominent set (top left) shows several waves moving from the northwest due to the tidal flow toward the north coast of Trinidad. Two less prominent sets can be seen further out to sea. All of these internal waves are probably caused by the shelf break near Tobago.

  The shelf break is the step between shal ow seas (around continents and islands) and the deep ocean. It is the line at which tides usual y start to generate internal waves.

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  Land of Lakes

  Canada

  During the last Ice Age, nearly all of Canada was covered by a massive ice sheet. Thousands of years later, the landscape still shows the scars of that icy earth-mover. Surfaces that were scoured by retreating ice and flooded by Arctic seas are now dotted with mil ions of lakes, ponds, and streams. In this false-color view from the Terra satel ite, water is various shades of blue, green, tan, and black, depending on the amount of suspended sediment and phytoplankton; vegetation is red.

  The region of Nunavut Territory is sometimes referred to as the “Barren Grounds,” as it is nearly treeless and largely unsuitable for agriculture. The ground is snow-covered for much of the year, and the soil typical y remains frozen (permafrost) even during the summer thaw. Nonetheless, this July 2001 image shows plenty of surface vegetation in midsummer, including lichens, mosses, shrubs, and grasses. The abundant fresh water also means the area is teeming with flies and mosquitoes.

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  Plankton and Sulfur

  Namibia

  Off the coast of Namibia, the Benguela Current flows north and west from South Africa. It is enriched by iron and other nutrients from the Southern Ocean and from dust blowing off African coastal deserts. Easterly winds push surface waters offshore and promote upwel ing near the coast, which brings up cold, nutrient-rich waters from the deeper ocean. These interactions can make the ocean come alive with color.

  Bacteria in oxygen-depleted bottom waters consume organic matter and produce large amounts of hydrogen sulfide. As that gas bubbles up into more oxygen-rich water, the sulfur precipitates out and floats near the surface in yel ow-green patches.

  Further offshore, milky green water may be a bloom of phytoplankton. As these organisms consume sunlight and nutrients, they also consume oxygen and sometimes deplete it from the water. At the same time, those oxygen-depleted waters help sulfur-producing bacteria thrive.

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  Åland Islands

  Scandinavia

  The Åland Islands lie in the Gulf of Bothnia, between Sweden and Finland. The archipelago consists of several large islands and roughly 6,500 small isles, many of them too small for human habitation. They are covered by pine and deciduous forest, meadows, and farmed fields. The region’s characteristic red rapakivi granite also stands out.

  These rocks were formed during the Proterozoic Eon, hundreds of mil ions of years before the dinosaurs. Massive ice sheets later sculpted the landscape, but these days people cut and use the granite in buildings and pavement. Landsat 5 acquired this image in June 2011.

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  Crater Lakes with Clear Water

  Canada

  About 290 mil ion years ago, two large asteroids smashed into Earth. The massive craters they left behind—now the Clearwater Lakes, or Lac à l‘Eau Claire—are still visible from space.

  When they struck, the binary asteroids crashed into a part of Earth’s crust that was fairly close to the Equator. Since then, mil ions of years of plate tectonics have pushed the craters northward into what is now northwestern Quebec. A mere 20,000 years ago, massive ice sheets advanced and retreated, scouring the land of soil and rock during cool periods and then carving deep channels and rinsing the landscape with meltwater during warmer periods. The erosion was so complete that many land surfaces were scraped down to underlying bedrock, exposing some of the oldest rocks in the world. Meanwhile, the meltwater from retreating glaciers left a dense network of linear lakes and streams that now dominate the surface.

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  Mergui Archipelago

  Southeast Asia

  Near the border of Burma (Myanmar) and Thailand, more than 800 islands rise amid extensive coral reefs in the Andaman Sea.

  This is the Mergui Archipelago.

  Captain Thomas Forrest of the East India Company first reported on the region to Europeans after a 1782 expedition, describing islands inhabited by a nomadic fishing culture. These people, known as the Moken, still call the archipelago home and mostly live a hunter-gatherer lifestyle. The small population of the archipelago has helped preserve its high diversity of plants and animals, making it a compel ing travel spot for ecotourism—both above and below the water line.

  In this view of Auckland Bay and Whale Bay, white swirling patterns in the near-shore waters are sediments that are carried out by rivers and deposited on the seafloor.

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  Scarlet Lake Natron

  Tanzania

  Lake Natron is mostly inhospitable to life, but it is gorgeous to the eye. The lake in Tanzania receives less than 500 mil imeters (20 inches) of rain in most years. Evaporation usual y exceeds that amount, and the lake needs input from some local rivers to maintain a water supply in the dry season.

  This Landsat 8 image from March 2017 shows Lake Natron’s chromatic c
harisma. Volcanism helps make the unusual color. Nearby volcanoes produce molten mixtures of sodium carbonate and calcium carbonate salts that move through faults and well up in hot springs. This briny, alkaline environment is too harsh for most common types of life, but salt-loving microorganisms (haloarchaea) bloom in the shal ow pools and impart pink and red colors to the water.

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  Swirling Bloom off Patagonia

  Argentina

  Interesting art often springs out of the convergence of different ideas and influences. And so it is with nature.

  Off the coast of Argentina, two strong ocean currents converge and often stir up a colorful brew, as shown in this Aqua image from December 2010.

  This milky green and blue bloom formed on the continental shelf off of Patagonia, where warmer, saltier waters from the subtropics meet colder, fresher waters flowing from the south. Where these currents col ide, turbulent eddies and swirls form, pul ing nutrients up from the deep ocean. The nearby Rio de la Plata also deposits nitrogen- and iron-laden sediment into the sea. Add in some midsummer sunlight, and you have a bountiful feast for microscopic, floating plants known as phytoplankton, which form the center of the ocean food web.

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  Earth and sky, woods and fields, lakes

  and rivers, the mountain and the sea,

  are excellent schoolmasters, and teach

  some of us more than we can ever learn

  from books.

  —John Lubbock

  The Use of Life

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  A Curious Ensemble of Wonderful Features

  United States

  When John Wesley Powell led an expedition down the Colorado River and through the Grand Canyon in 1869, he was confronted with a daunting landscape. At its highest point, the serpentine gorge plunged 1,829 meters (6,000 feet) from rim to river bottom, making it one of the deepest canyons in the United States. In just 6 mil ion years, water had carved through rock layers that col ectively represented more than 2 bil ion years of geological history.

  “The wonders of the Grand Canyon cannot be adequately represented in symbols or speech,” Powell wrote in his log. Powell was seeing the canyon mainly from river level; there was no technology that provided views of the landscape from space then. If there had been, he would have seen something similar to what Landsat 8 observed in March 2013.

  The Colorado River traces a line across the arid Colorado Plateau. Treeless areas are beige and orange; green areas are forested.

  The river water is brown and muddy, a common occurrence in spring when melting snows cause water levels to swell and pick up extra sediment.

  It took Powell months to navigate the gorge. By the time he had arrived in the area that is now Lake Mead (visible on the next page, far left), his men were weary and four had deserted. For water and sediment transported by the Colorado, the journey is much quicker; it takes just a handful of days.

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  Megadunes and Desert Lakes

  Mongolia

  In the Badain Jaran, nearly 100 lakes mingle with the tal est sand dunes in the world. Researchers have long studied these features in China, yet mystery continues to enshroud them.

  Situated in the Alxa Desert region of Inner Mongolia, the Badain Jaran natural y piles up megadunes towering 200 to 300 meters (650 to 1,000 feet) tal . Scientists are still puzzling over how the dunes grow so large, investigating a combination of wind patterns and underlying geology.

  Another enigma is the source of water for the lakes. Scientists are working to figure out the relative contributions from precipitation, groundwater, snowmelt, and paleowater. Regardless of the water source, they know that some lakes have shrunk or disappeared in recent years.

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  Colorful Faults of Xinjiang

  China

  Just south of the Tien Shan mountains, in northwestern Xinjiang province, a remarkable series of ridges dominates the landscape.

  The hil s are decorated with distinctive red, green, and cream-colored sedimentary rock layers. The colors reflect rocks that formed at different times and in different environments. The red layers near the top of the sequence are Devonian sandstones formed by ancient rivers. The green layers are Silurian sandstones formed in a moderately deep ocean. The cream-colored layers are Cambrian-Ordovician limestone formed in a shallow ocean.

  Landsat 8 captured this image of the Keping Shan thrust belt in July 2013. When land masses col ide, the pressure can create what geologists call “fold and thrust belts.” Slabs of sedimentary rock that were laid down horizontal y can be squeezed into wavy anticlines and synclines. Sometimes the rock layers break completely, and older layers of rock pile up on top of younger layers.

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  Bowknot Bend

  United States

  This section of the Green River canyon in eastern Utah is known as Bowknot Bend because of the way the river doubles back on itself. The loop carries river rafters 14.5 kilometers (9 miles) before bringing them back to nearly the same point they started from—

  though on the other side of a low, narrow saddle. The reason for the tight bends in the Green River is the same as it is for the mighty Mississippi: river courses often wind over time when they flow across a bed of relatively soft sediment in a floodplain.

  In this January 2014 photograph taken from the International Space Station, the Green River appears dark because it lies in deep shadow, 300 meters (1,000 feet) below the surrounding landscape. The yel ow-tinged cliffs that face the rising Sun give a sense of the steep canyon wal s. The straight white line across the scene is the contrail from a jetliner.

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  From Rainforest to Rain Shadow

  United States

  Within a three-hour drive across Oregon, you can visit a beach, a temperate rainforest, a mountain glacier, and the high desert.

  The diversity of the landscape is mostly driven by the interaction of air masses and mountains.

  This false-color Landsat 5 image from October 2011 shows the bare soil and sparse vegetation of the high desert in shades of pink, together with the deep-green vegetation on the west side of the Cascade Mountains. The one blue spot is the glacial cap of Mount Hood.

  The transition from green to brown is indicative of a “rain shadow.” Winds blowing from the west carry moisture from the Pacific Ocean. As the air moves up into the mountains, it cools and the pressure decreases; the moisture condenses and fal s out as rain or snow. On the eastern side, as the elevation drops, the air pressure increases and the air warms, effectively shutting off precipitation because the air can better hold the remaining moisture.

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  A Blaze of Color

  Sweden

  Fall in northern Sweden is a brief but spectacular affair. Alpine forests in this remote part of Lapland turn blazing shades of yel ow and orange. Landsat 8 captured this image in October 2016.

  Birch forests growing along stream val eys are probably the source of most of the color here, though other deciduous shrubs and understory plants surely contribute as wel . Some of the hil s have a dusting of snow. The southern Sun’s low angle above the horizon draws long, dark shadows across the landscape.

  In autumn, the leaves on deciduous trees change colors as they lose chlorophyl , the pigment that helps plants synthesize food.

  When days shorten and temperatures drop, levels of chlorophyll (which appears green) do as wel . Other leaf pigments—carotenoids and anthocyanins—then show off their colors.

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  Folds and Curves of the
Kavir

  Iran

  When astronauts pass over the deserts of central Iran, they are greeted by a striking pattern of paral el lines and sweeping curves.

  The lack of soil and vegetation in the Kavir desert (Dasht-e Kavir) al ows the geological structure to appear quite clearly.

  The patterns result from the gentle folding of numerous, thin layers of rock. Later, erosion by wind and water cut a flat surface across the dark- and light-colored folds, not only exposing hundreds of layers but also showing the shapes of the folds. The pattern has been likened to the layers of a sliced onion.

  The dark water of a lake (image center) fil s a depression in a more easily eroded, S-shaped layer of rock. A small river snakes across the bottom of this October 2014 photograph taken from the International Space Station.

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  Fanning Out in Farmland

  Kazakhstan

  Mountain streams are usual y confined to narrow channels and tend to transport large amounts of gravel, sand, clay, and silt—

  what geologists call al uvium. When such a stream pours onto a relatively flat val ey or basin, it often spreads out to into multiple, interlacing channels. Over time, the channels migrate back and forth, creating fan-shaped deposits known as al uvial fans.

  Landsat 8 captured this view of Kazakhstan’s Almaty Province in September 2013. On the lower left, the Tente River flows through the foothil s of the Dzungarian Alatau range. Where the Tente emerges, it spreads out and becomes a braided stream. The movement of the channel over time has left a large al uvial fan. In arid areas, these fans are often used for agriculture because they are relatively flat and provide groundwater for irrigation. The blocky green patterns show fields or pasture land.