Alluvial Fan, CaliforniaDepositional Landform Pictures. Photo (c) 2007 Andrew Alden, licensed to About.com ( fair use policy)
There are different ways to classify landforms, but generally, there are three categories: landforms that are built (depositional), landforms that are carved (erosional), and landforms that are made by movements of the Earth's crust (tectonic). Here are the most common depositional landforms.
More Types of Landforms
- Erosional Landforms
- Tectonic Landforms
An alluvial fan is a wide pile of sediment deposited where a river leaves the mountains.
Click the photo to see the full-size version of Deception Canyon fan, near Palm Springs. When mountains shed sediment off their flanks, streams carry it away as alluvium. A mountain stream carries lots of alluvial sediment easily when its gradient is steep and energy is abundant. When the stream leaves the mountains and debouches onto the plain, it drops most of that alluvial sediment immediately. So over thousands of years, a wide cone-shaped pile builds up -- an alluvial fan. A steep-sided fan may instead be called an alluvial cone.
Alluvial fans are also found on Mars.02of 19
Bajada, CaliforniaDepositional Landform Pictures. Photo (c) 2009 Andrew Alden, licensed to About.com ( fair use policy)
A bajada ("ba-HA-da") is an extensive apron of sediment, the sum of many alluvial fans. It typically covers the foot of a whole range, in this case, the eastern face of the Sierra Nevada.03of 19
Bar, CaliforniaDepositional Landform Pictures. Photo (c) 2007 Andrew Alden, licensed to About.com ( fair use policy)
A bar is a long ridge of sand or silt, laid down wherever conditions call for a current to stop and drop its load of sediment.
Bars may form wherever energetic bodies of water meet: at the meeting of two rivers or where a river meets the sea. Here at the mouth of the Russian River, the river's current meets the onshore-pushing surf, and in the endless battle between the two, the sediment they carry is deposited in this graceful pile. Larger storms or high river flows may push the bar one way or the other. In the meantime, the river gets its business done through the small channel that cuts across the bar.
A bar is often also a barrier to navigation. Thus a sailor may use the word "bar" for a ridge of bedrock, but the geologist reserves the word for a pile of alluvium -- the material carried by streams -- under the influence of water.04of 19
Barrier Island, New JerseyDepositional Landform Pictures. Photo (c) 2007 Andrew Alden, licensed to About.com ( fair use policy)
Barrier islands are long, narrow ridges of sand raised by waves between the ocean and the coastal lowlands. This is in Sandy Hook, New Jersey.
Beach, CaliforniaDepositional Landform Pictures. Photo (c) 2006 Andrew Alden, licensed to About.com ( fair use policy)
Beaches are probably the most familiar depositional landform, made by wave action that piles sediment against the land.06of 19
Delta, AlaskaDepositional Landform Pictures. Photo by Bruce Molnia, U.S. Geological Survey
Where rivers meet the sea or a lake, they drop their sediment, which extends the coast outward in a landform ideally shaped in a triangle.07of 19
Dune, CaliforniaDepositional Landform Pictures. Photo (c) 2008 Andrew Alden, licensed to About.com ( fair use policy)
Dunes are made of sediment carried and deposited by wind. They keep their characteristic shapes even as they move. The Kelso Dunes are in the Mojave Desert.
Floodplain, North CarolinaDepositional Landform Pictures. Photo courtesy David Lindbo under Creative Commons License
Floodplains are flat areas along rivers that receive sediment whenever the river overflows. This one is in New River, North Carolina.09of 19
Landslide, CaliforniaDepositional Landform Pictures. Photo (c) 2003 Andrew Alden, licensed to About.com ( fair use policy)
Landslides, in all their variety, involve sediment leaving high places and piling up in low places. Learn more about landslides here and view this landslide gallery.
Lava Flow, OregonDepositional Landform Pictures. Photo courtesy bdsworld of Flickr.com under Creative Commons license
Lava flows range from this stiff obsidian pile at Newberry Caldera to huge basalt plateaus that hardened from lakes of molten rock.11of 19
Levee, RomaniaDepositional Landform Pictures. Photo courtesy Zoltán Kelemen of Flickr.com under Creative Commons License
Levees form naturally between a river's banks and the floodplain around it. They are usually modified in inhabited places.
Levees form as rivers rise over their banks for a very simple reason: the current slows at the water's edge, therefore part of the sediment load in the water is dropped on the banks. Over many floods, this process builds up a gentle rise (the word comes from the French levée, which means raised). When humans come to inhabit a river valley, they invariably fortify the levee and raise it higher. Thus geologists take pains to specify a "natural levee" when they find one. The levees in this picture, in Transylvania, Romania, may have an artificial component, but they are typical of natural levees -- low and gentle. Levees also form underwater, in submarine canyons.
Mud Volcano, CaliforniaDepositional Landform Pictures. Photo (c) 2007 Andrew Alden, licensed to About.com ( fair use policy)
Mud volcanoes range widely in size and shape from little squirters up to full-sized hills that erupt with flaming gas.
A mud volcano is usually a small, very temporary structure. On land, mud volcanoes are found in two types of places. In one, volcanic gases rise through fine sediments to cause small eruptions and build cones of mud no more than a meter or two high. Yellowstone and places like it are full of them. In the other, gases bubble up from underground deposits -- from hydrocarbon traps or where carbon dioxide is being liberated in metamorphic reactions -- into muddy places. The largest mud volcanoes, found in the Caspian Sea region, reach a kilometer in breadth and several hundred meters in height. The hydrocarbons in them burst into flame. This mud volcano is part of the Davis-Schrimpf seep field, near the Salton Sea in southern California.
Under the sea, mud volcanoes also occur in two types. The first is the same as those on land, built by natural gases. The second type is a major outlet for fluids released by subducting lithospheric plates. Scientists are only beginning to study them, most notably on the western side of the Marianas Trench region.
"Mud" is actually a precise geological term. It refers to sediments made of a mixture of particles of the clay and silt size range. Thus a mudstone is not the same as a siltstone or claystone, though all three are types of shale. It's also used to refer to any fine-grained sediment that varies a lot from place to place, or whose exact composition isn't well determined.
Playa, CaliforniaDepositional Landform Pictures. Photo (c) 2002 Andrew Alden, licensed to About.com ( fair use policy)
Playa (PLAH-yah) is the Spanish word for beach. In the United States, it is the name for a dry lake bed.
Playas are the resting place of fine sediment shed from the mountains around them. The playa of Dry Lake Lucerne is in the Mojave Desert of southern California, on the other side of the San Gabriel Mountains from the Los Angeles region. The mountains keep away the moisture of the Pacific Ocean, and the lake bed only holds water in unusually wet winters. The rest of the time, this is a playa. The dry parts of the world are dotted with playas. Learn more about playas.
Driving across (and upon) a playa is a heady experience for someone used to streets. A Nevada playa called the Black Rock Desert takes this geologic setting as a natural stage for free artistic and cultural expression in the Burning Man festival.14of 19
Spit, WashingtonDepositional Landform Pictures. Photo courtesy WordRidden of Flickr.com under Creative Commons License
Spits are points of land, usually of sand or gravel, that extend from shore into a body of water.
Spit is an ancient English word that also refers to the skewers used for roasting food items; related words are spike and spire. Spits form as sand is transported by longshore drift into open water like an inlet, river or strait. A spit may be an extension of a barrier island. Spits can extend for kilometers but are usually short. This is Dungeness Spit in Washington, which extends into the Strait of Juan de Fuca. At approximately 9 kilometers, it's the longest spit in the United States, and it continues to grow today.
Tailings, CaliforniaDepositional Landform Pictures. Photo (c) 2009 Andrew Alden, licensed to About.com ( fair use policy)
Tailings -- waste material from excavations -- cover significant amounts of land and affect the terrestrial cycle of erosion and sedimentation.
Gold dredgers in the 1860s systematically dug up all the gravel in this California riverbed, washed out its small fraction of gold, and dumped the tailings behind them. It is possible to do this kind of hydraulic mining responsibly; a catchment pond settles out the clay and silt to protect the downstream environment, and the tailings can be graded and replanted. In a large land with few inhabitants, some degradation can be tolerated for the wealth that's created. But during the California gold rush, there was plenty of irresponsible dredging. The rivers of the Sierra Nevada and the Great Valley were so severely disturbed by tailings that navigation was hampered and farms failed after being flooded with sterile mud. The state legislature was ineffective until a federal judge banned hydraulic mining in 1884. Read more about it on the Central Pacific Railroad Photographic History Museum site.
A recent study concluded that all the work we do in moving rock, water and sediments around makes humankind a significant geomorphic agent just like rivers, volcanoes, and the rest. In fact, human energy is more effective than all the world's erosion at the moment.
Terrace, OregonDepositional Landform Pictures. Photo (c) 2005 Andrew Alden, licensed to About.com ( fair use policy)
Terraces are flat or gently sloping constructions made of sediment. This terrace marks an ancient lakeshore.
This beach terrace marks an ancient shoreline of Summer Lake in south-central Oregon, the Oregon Outback. During the ice ages, lakes occupied most of the wide, flat valleys in the Basin and Range province of the American West. Today those basins are mostly dry, many of them desolate playas. But when the lakes existed, sediment from the land settled along the shorelines and created long level beach terraces. Often several paleo-shoreline terraces appear on the basin's flanks, each one marking a former shoreline, or strandline. Also, sometimes the terraces are distorted, yielding information about tectonic movements since the time they formed.
Strandlines along the seacoast may have similarly raised beaches or wave-cut platforms.17of 19
Tombolo, CaliforniaDepositional Landform Pictures. Photo (c) 2002 Andrew Alden, licensed to About.com ( fair use policy)
A tombolo is a bar that extends outward from the shore, connecting with an island. In this case, the bar is reinforced to serve as a parking lot. (more below)
Tombolos (accent on the "TOM") form as an offshore hill, or stack, bends incoming waves around it so that their energy sweeps sand together from both sides. Once the stack erodes down to the waterline, the tombolo will disappear. Stacks don't last long, and that's why tombolos are uncommon.
See this article for more about tombolos, and see this gallery for more pictures of tombolos.18of 19
Tufa Towers, CaliforniaDepositional Landform Pictures. Photo (c) 2006 Andrew Alden, licensed to About.com ( fair use policy)
Tufa is a porous variety of travertine that forms from underwater springs. Mono Lake's water level was lowered to reveal its tufa towers.19of 19
Volcano, CaliforniaDepositional Landform Pictures. Photo (c) 2006 Andrew Alden, licensed to About.com ( fair use policy)
Volcanoes are unlike other mountains in that they are built (deposited), not carved (eroded). See the basic types of volcanoes here.