Visual Geography: the Shape of Land Near the Oceans

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There are a lot of geography terms to describe how land is formed around water. Here is a visual dictionary of geography words that describe some of the landforms found near ocean water.

Land forms

The land masses on Earth can be categorized into three main groups: continental mainlands, big islands, and small islands.

Continents are the largest contiguous land forms that exist. Depending on how the land masses are categorized there are between 4 and 7 continents in the world.

The minimum number of continents is four: Afro-Eurasia, America, Antarctica, and Australia.  In the four-continent model, all of the connected landmasses are counted as one continent.

The Americas, which consists of North America, Central America, and South America is considered as one large continent. Likewise, Europe, Asia, and Africa are also considered as one large continent. Australia and Antarctica make up the other two continents.

A map showing the world divided into four main continents.  The Americas are shaded in light blue, Europe, Africa, and Asia form Acro-Eurasia and is shaded in light orange.  Australia is shaded light green and Antarctica is shaded in light gray.
Map of the four continent model. Map: Caitlin Dempsey, Sphere Natural Earth map projection.

Different combinations of recognizing Africa, Europe, and Asia as separate continents alters the number up to a total of seven continents: Africa, Antarctica, Asia, Australia, Europe, North America, and South America.  

Map showing the different continents in light shades of color for a total of seven continents.
Map showing the seven continent model. Map: Caitlin Dempsey.

Continental mainlands are just the large landforms without the offshore islands.

Big islands are those islands that have an area that is greater than one square kilometer. The Global Islands dataset created by the the U.S. Geological Survey (USGS) and Esri, a GIS software company, estimates there are 21,818 big islands in the world.

Small islands are those islands with a land area that is less than one square kilometer. The Global Islands dataset contains 318,868 small islands.

Islands

Archipelago

An archipelago is a group of islands. For example, the Hawaii Islands is an archipelago that consists of eight major islands, several atolls, and numerous smaller islets in the North Pacific Ocean.

The Cape Verde Archipelago is located about 400 miles (650 kilometers) off Senegal’s coast. An island country, Cape Verde is comprised of ten volcanic islands.

The highest point in the Cape Verde Archipelago is Pico de Cano, a stratovolcano on the island of Fogo with a peak of 9,281 feet (2,829 meters).

A map showing the ocean as light blue and a an archipelago with labels for the islands names off of a grey shaded mainland.
Map showing the Cape Verde Archipelago. Map: Caitlin Dempsey.

Barrier Islands

Barrier islands are narrow stretches of land that run parallel to coastlines.

These islands, which are made of deposited sand and vegetation, can act as protective barriers that lessen coastal erosion, clean the water, and aid in the preservation of plants and animals.

Barrier islands can extend for miles along the coast and are isolated from the mainland by a shallow body of water.

Except for Antarctica, all continents have barrier islands off the mainlands. The Northern Hemisphere is home to 74% of the world’s barrier islands.

The largest and longest barrier island in the world is Padre Island off the coast of Texas.

A map showing the location of Padre Island off the coast of Texas.  The island is in light yellow with a green area for the National Seashore.  The mainland of Texas is grey and a small white area in the bottom left corner is for Mexico.
Padre Island is a large barrier island located off the coast of Texas. Map: Caitlin Dempsey.

Atolls

Atolls are ring-shaped islands with a hollow center that forms a lagoon.

Atolls are created when coral reefs develop a fringing reef on the edges of a former island. As the island subsides due to erosion from wind and ocean waves, the coral reef formation with a lagoon is left behind.

Step by step diagram showing how an atoll forms from a subsiding island with a volcano.
An illustration showing how atolls are formed. Image: U.S. Coral Reefs—Imperiled National Treasures, USGS, public domain.

Atolls have long, thin bars of white sand that rise just a few meters above sea level. Limited soil that develops on top of the calcium-rich skeletons of coral and other reef dwellers can submit some vegetation which can include palm and breadfruit trees.

Satellite image of an atoll with the dark blue ocean water surrounding the atoll.
Tureia, an atoll, in French Polynesia, in the South Pacific Ocean. Image; NASA via USGS, public domain.

About 60% of the corals reefs in the United States are found coral in the extended Hawaiian Island chain.

Located in the Hawaii island archipelago, Kure atoll has a diameter of 5.8 miles (9.3 kilometers). Kure Atoll was formed on the site of a former volcano and is the northernmost coral atoll in the world.

An aerial photograph of the Kure Atoll showing light blue waters in the lagoon and darker blue waters in the open ocean.
Kure Atoll in the Hawaiian Island Chain. The center of the atoll is a lagoon. Photo: USGS, public domain.

Isthmus

An isthmus is a type of land bridge that is a small section of land connecting two larger land masses that has open waters such as a sea on both sides.

One of the largest isthmuses is the Isthmus of Panama which is a narrow strip of land that connects North America and South America. The Isthmus of Panama covers the country of Panama and extends from the Colombian border to the Costa Rican border.

The Isthmus of Panama is  400 miles (640 kilometers) long.

Map showing the Isthmus of Panama with the land areas in yellow and the ocean in blue.
The Isthmus of Panama connects the continents of North and South America. Map: Caitlin Dempsey.

Another famous isthmus is the Isthmus of Suez which is 75 miles (125 kilometers) long.

Peninsula

A peninsula is a piece of land that is surround on three sides by ocean. The word peninsula originates from the Latin words paene ‘almost’ and insula ‘island’.

There are peninsulas on every continent. The largest peninsula is the Arabian Peninsula.

In the United States, the most recognizable peninsula is the lower two-thirds of the state of Florida. The peninsula is located between the Gulf of Mexico, the Florida Strait, and the North Atlantic Ocean.

Map showing the state of Florida in light gray with major cities labeled and a light blue ocean.
Map of Florida. Map: Caitlin Dempsey, Natural Earth data.

Cape

A cape is a small section of land that extends past the coastline into the ocean.

Cape Cod in Massachusetts is a well-known example of a cape. The cape looks like a flexed arm when viewed from space.

Cape Cod juts into the Atlantic Ocean from the southeastern corner of mainland Massachusetts. Cape Cod was formed from the sediment deposits scraped from the Earth by retreating glaciers after the last major ice age.

Annotated satellite image of Cape Code showing green for the land and dark blue for the ocean.
Landsat 8 image of Cape Cod, 2014. Image: NASA, public domain.

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