River, MountainsTinayguk River, Gates of the Arctic National Park and Preserve, AlaskaPhotograph by Michael Melford

MountainMount Doubletop, Baxter State Park, Maine

MountainsDingle, Ireland

Freshwater MarshOkavango Delta, BotswanaThe world’s largest freshwater marsh, where the Okavango River meets the Kalahari desertPhotograph by Lorenzo Manni, MyShot

Rocky CoastMonhegan Island, MaineA coastline is the area where land meets sea or ocean.

Beach, Cliffs, PlainDunmore Head, Dingle Peninsula, IrelandA beach is a narrow strip of land that lies along a body of water.

Sandstone Spire, CliffsSpider Rock, Canyon de Chelly, ArizonaA cliff is a steep, near-vertical rock exposure, formed by erosion and weatheringPhotograph by Bill Hatcher

ButteThe “Lighthouse,” Palo Duro Canyon, TexasAn isolated hill with steep sides and a flat top, smaller than a mesa, formed by erosionPhotograph by Anthony Boyer, MyShot

CanyonGrand Canyon ValleyA canyon is a deep, narrow valley with steep sides,created by the movement of rivers, erosion and weathering. Photograph by Barry Tessman

Natural ArchDelicate Arch, Arches National Park, Moab, UtahFormed by erosion and weatheringPhotograph by Mlcreech

Mesa“Great White Throne,” Zion National Park, UtahA mesa is a flat-topped mountain, this one made of limestone.Photograph by James P. Blair

CliffInishmore, IrelandA cliff is a steep, near-vertical mass of rock, this one made of limestone

BayouAdams Bayou, Orange, TexasA slow-moving body of water

River BedColorado River Bed, Grand CanyonPhotograph by Wilbur E. Garrett

Waterfall, Cliffs, IslandBaffin Island Waterfall, Nunavut, CanadaPhotograph by Paul Nicklen

River, Canyon, PlateauOwyhee River, IdahoPhotograph by Michael Melford, National Geographic, aerial support from Lighthawk

Sand DunesSand dunes of Khongoryn Els, Gobi Gurvansaikhan National Park, Ömnögovi Province, MongoliaCrescent-shaped sand dunes are created by winds that blow continuously from one directionPhotograph by Doron

DesertTecopa, Mojave Desert, CaliforniaEvaporation of a flooded dry lake caused these cracks in the mud.Photograph by Lorenzo Manni, MyShot

Sand Dunes and HillsInishowen, IrelandPhotograph by Dave Johnston, YourShot

PlainsSichuan, ChinaA plain is a broad area of flat land.Photograph by Xi Luo, MyShot

HillsPainted Hills, OregonLand that rises above its surroundings and has a rounded summitPhotograph by Michel Hersen, MyShot

GeyserCastle Geyser, Yellowstone National ParkA geyser is a natural hot spring that sometimes erupts with water or steam.Photograph by Brocken Inaglory

VolcanoesMount Semeru, JavaAn opening in the earth’s crust from which hot magma, volcanic ash, and gas erupt.Photograph by John Stanmeyer, National Geographic

Volcanic CraterSanta Ana Volcano, El SalvadorA circular depression caused by volcanic activity