What Is a Tied Island?

St. Ninian's Isle on the coast of Shetland, Scotland.
St. Ninian's Isle on the coast of Shetland, Scotland.

A tied island refers to an island which is connected to the mainland by a narrow piece of land called a tombolo. Refraction and diffraction of waves are responsible for the formation of the tied island. Waves slow down as they approach an island, and the shallow water around the island causes waves to bend to the opposite side. This movement pushes sediment onto the lee side of the islands, causing accumulation over time, and eventually a strip of land emerges connecting the island to the mainland, and thus forming a tied island. Some of the major tied islands around the world are listed below.


Barrenjoey is located in New South Wales, Australia. It was part of the mainland until 10,000 years ago, when it was cut-off by the rising sea level and a build-up of sandpits. The island was given its current name by Arthur Phillip in 1788. It is the location of the famous Barrenjoey Head Lighthouse.

Naval Air Station North Island

Naval Air Station North Island is located in the Coronado peninsula, San Diego, United States. It is a vast mass of land connected to the mainland by an equally prominent tombolo. The tied island is so big that it serves as an air base for the U.S. Navy. The island was initially known as North Coronado Island after it was separated from the mainland by a shallow bay which filled up in 1945 to create the current landform that it is today.

Isle of Portland

The Isle of Portland is an island made of limestone that measures 4 miles long by 1.7 miles wide, and is located in the English Channel. Humans have occupied the tied island since the Mesolithic period, and has since been controlled by different conquerors,cluding the Romans. The isle has two main areas that define its geography: a steeply sloping landmass to the north called Underhill, and an opposite gently sloping area called Tophill. The isle is home to the Portland Bill Lighthouse.

Scotts Head

Scotts Head is a village situated on a tied island on the coast of Dominica. The land has a range of about 17 nautical miles and is the only tied island in the Caribbean region. The island was named after Colonel George Scott, who was part of the British invasion of Dominica. Ownership later changed hands to the French in the 1700s.

St. Ninian’s Isle

St. Ninian's Isle is located in the United Kingdom, and is a small tied island that is joined to the mainland by the UK's largest tombolo. The island is about 72 hectares in size and is home to some rare seabirds, such as puffins. Every summer, the tombolo that is 1,640 feet long and serves the island rises above the sea level. However, during the winter, the strong waves remove the sand and the tombolo cannot be used until spring.

The Significance of Tied Islands

Most tied islands have provided a haven for endangered species of animals and plants. Being small in size means they cannot support human populations, and therefore many are converted into sanctuaries that are free from human interference. However, others have been turned into tourist attractions, since their lighthouses and beautiful landscapes are considered perfect places to go for a vacation or camping.


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