A taiga, also called a boreal forest, is a forest located in the subarctic zone, which is the region just below the Arctic Circle in the Northern Hemisphere. Situated between the vast arctic tundra and more temperate forests to the south, taigas are common in Scandinavia, Canada, and Alaska. The world’s largest taiga is located in Siberia, Russia.

Streams or creek beds that are typically dry but fill up after heavy rainfall are called “arroyos,” which is Spanish for “dry streams.” Arroyos are typically seasonal and can be natural or human-made. They are very common in the American Southwest because of the arid climate, with long dry spells and subsequent rainy seasons. The Arroyo Seco and the Los Angeles River in Southern California are examples of prominent arroyos.

Vernal pools are seasonal wetland habitats that fill up in the spring by rain and snowmelt and dry up during the summer. Their temporary dryness distinguishes them from other types of permanent wetlands like swamps, marshes, and bogs. The word “vernal” itself is a clue to this wetland’s name — it means “relating to the spring,” as in the vernal equinox, or spring equinox.

Plateaus come in two types: dissected and volcanic. Volcanic plateaus happen when, over time, magma rises up beneath the Earth’s surface without breaking it. The plateau rises when the lava continues to flow in that area. Dissected plateaus form when tectonic plates slowly move together, pushing the Earth’s crust upward.

An oxbow lake forms when a river meanders and finds a new (usually shorter) route. This causes part of the river to eventually be cut off from the rest, forming a small, curved lake. Oxbow lakes are stillwater lakes, meaning that water does not flow to or from them anymore. They are often temporary, usually becoming swamps or bogs before drying up completely.

A skerry is a rocky islet that is typically not large enough for humans to live on. Mostly formed by glacial erosion, they’re common along the high-latitude coastlines of Norway, Iceland, and Greenland, as well as other areas of the Northern Hemisphere. The term “skerry” comes from the Old Norse word “sker,” which means “rock in the sea.”

The French word for “ridge,” an arête is a thin ridgeline that separates two cirques, or circular basins formed by glaciers. After a glacier carves out steep bowls on either side of a mountain, it leaves behind a sharp ridgeline which is referred to as an arête. A common example is the Garden Wall in Montana’s Glacier National Park, a famous landform known for its razor-thin arêtes.

A bight is a long, gradual bend in a coastline that forms a large, open bay. Bights can be found all over the world, but some of the most well-known are the Southern California Bight, which runs from Point Conception near Santa Barbara to San Diego, and the Great Australian Bight, which covers much of the continent's southern coast.

Also known as sand seas, ergs are areas of deserts covered in massive amounts of sand that have little to no vegetation. Generally, these geographic regions are found at the bottom of enormous basins, where ancient rivers have accumulated sandy deposits. In an erg, the sand is generally loose and extremely difficult to traverse. The term "erg" is derived from an Arabic word meaning "dune field."

Karsts are made of limestone — not just a few pieces of limestone, but massive formations over miles of land. What makes limestone unique is its softness, which means it erodes and soaks up water easily. Water from precipitation and rivers flows around and through the rocks, carving them into incredible formations. Due to this, karsts are known for their immense cave systems, sinkholes, underground rivers and lakes, and jagged shapes.

When a glacier moves across an area, it leaves a deep, U-shaped groove in the land. The neighboring sea then fills the new valley, forming a deep river inlet through coastal lands. Often, the remaining rocks and sediment will stay near the fjord’s entrance, making for deeper water the farther inland you go.

Pronounced “seh-no-tay,” a cenote is a cave that contains a sinkhole of deep water that is fed from a current of subterranean rivers and rainwater. Mexico’s Yucatan peninsula is famous for its abundance of cenotes, part of the region’s vast cave system. The term comes from the ancient Mayans, who called these sinkholes dz’onot, which translates to “cavern with water.”

Hoodoos are tall, skinny columns of rock with distinctive shapes formed by centuries of erosion. Harder rock types are layered on top of softer sedimentary rocks, so the lower parts of the columns are more eroded while larger rocks seem to balance precariously atop. Hoodoos exist on every continent, but Utah's Bryce Canyon is home to the greatest concentration of hoodoos on the planet.

An isthmus is a strip of narrow land surrounded by water that connects two landmasses. One of the ways an isthmus can form is after a volcanic eruption makes islands in a channel. The blockage collects sediment, which becomes a continuous strip of land, like the Isthmus of Panama. An isthmus can be as narrow as a few miles wide or hundreds of miles across.

A tarn is a small mountain lake that forms in bowl-shaped valleys carved out by glaciers, known as cirques. Once the glacier has melted away, rainwater or river water flows into the depression left by the glacier, creating a tarn (also known as a rock-basin lake). The term "tarn" is derived from an Old Norse term meaning "pond."

When a freshwater river empties into an ocean, it creates a brackish area (where freshwater and saltwater combine) called an estuary. Estuaries are sometimes named as a bay or a sound, depending on their size. For example, Washington state's Puget Sound is an estuary whose coastline is dotted with rivers and streams that empty fresh water into the icy waters of the northern Pacific Ocean.

A butte — a tall, flat-topped rock tower with steep sides — forms gradually as a river erodes its caprock. Because caprock resists weathering, buttes are much taller than they are wide, unlike the mesa from which they’re formed. Typically, buttes are in dry areas, where wind and rain erode the weaker rock beneath the caprock, creating unique pillar-like shapes.

Deltas were named for their triangular shape, making them easy to spot. They form where a river meets the ocean when currents deposit sediment near standing water. You can sometimes find deltas in lakes, and if a river distributes itself in a specific way, it can create a series of deltas, like at the mouth of the Mississippi River.

An archipelago is an area that contains a chain or group of islands. Indonesia is made up of five major islands — Sumatra, Java, Borneo, Sulawesi, and New Guinea — plus over 17,500 smaller ones. Less than half of these islands are inhabited, and the archipelago is also home to about 100 active volcanoes. Several of Indonesia’s islands are also popular tourist attractions, including Bali, Ubud, and Kuta.

Straits typically connect two seas or oceans and are crucial to world trade and transportation. One of the most important straits in the world, the Strait of Gibraltar, connects the Atlantic Ocean to the Mediterranean Sea. Straits can also connect bodies of water; the Golden Gate Strait, for example, connects San Francisco Bay to the Pacific Ocean.