Motu One, Tubuai, French Polynesia; By Andrew Cooper

Posted In Beach of the Month, Features

By Andrew Cooper, University of Ulster

Tubuai is a small island in the Austral Island Group of French Polynesia, about 600km south of Tahiti.
The volcanic island is surrounded by a lagoon and a nearly continuous reef. On the reef flat there are several small islands of sand and coral rubble, known as motus.

Most motus are quite well vegetated, but one small example at Tubuai is completely bare and composed of a white coral sand beach. Called Motu One (pronounced O-nay), it is barely 250m long and 50m wide and is located on the reef crest on the north side of Tubuai.

The fact that such a small and isolated pile of sand survives even hurricanes is a perfect illustration of the ability of natural beaches to adapt to changing conditions….
—Andrew Cooper

On its seaward edge, Motu One has a ridge of beachrock which encloses a small lagoon. There are also a few small patches of beachrock on the lagoon side of the motu. The motu is affected by ocean waves on the north side and lagoon waves on the south and so water flows into the enclosed lagoon from both sides.

The seaward-facing beach is very steep but it is sheltered from the direct effect of ocean waves by the reef platform that absorbs a lot of the incoming wave energy. On the lagoon side, waves are less energetic but they are still able to carry sand and shells onto the beach surface.

The motu has changed shape several times but is anchored by the beachrock that helps keep it in place.

Motu One survived Hurricane Oli in 2011, which caused much damage on adjacent Motus and beaches on mainland Tubuai. The fact that such a small and isolated pile of sand survives even hurricanes is a perfect illustration of the ability of natural beaches to adapt to changing conditions.

The accompanying photos (supra) show the motu sitting on the reef crest, the beachrock ridge on its seaward side and the small lagoon that it encloses. The steep slope on the seaward-facing beach contrasts with the more gentle slope of the beach on the island side.


More / Beach Of The Month

Torrevieja, Spain; By Norma J. Longo

January 1st, 2018

Torrevieja, a former fishing village on the southeast coast of Spain (Costa Blanca) in Alicante province, is now a thriving tourist city with a 2016 population of around 85,000, down from a high of over 105,000 in 2013.

Read More

The rugged coast and black sand beaches of the Azores; By Gary Griggs

December 1st, 2017

A soft, white sandy beach on a lush green island is probably the vision many people have of their perfect coastal vacation. Eight hundred and fifty miles west of Portugal and 2400 miles east of Boston lies the lush island of São Miguel in the Azores. It is one of nine islands making up an archipelago spread across 300 miles of the North Atlantic Ocean.

Read More

Colombia’s Tayrona National Natural Park: A Caribbean Coast Gem; By Nelson Rangel-Buitrago & William J. Neal

October 1st, 2017

Colombia’s Caribbean coast has a rich geological, biological and cultural diversity that is reflected in the complex coastal zone extending from the border of Panama to that of Venezuela. One of the most spectacular regions in both this diversity and scenery is the Tayrona National Natural Park (TNNP).

Read More

The end of the world’s most famous beaches; By Orrin H. Pilkey and J. Andrew G. Cooper

August 1st, 2017

All over the world there are beaches lined with condos, hotels, restaurants and the like, in high-rise buildings (i.e., skyscrapers). Such beaches are generally the nation’s premier tourist areas, important to the local people and the local economy and prime spots for national and international vacationers. The powers that be in most of these places continue high-rise construction and seem oblivious of the sea level rise.

Read More

The natural bridges of Santa Cruz County; By Gary Griggs

June 1st, 2017

While most coastlines often appear to be stable and permanent over the short time span of our visits, and some are, there are many others where the materials making up the coastal bluffs or cliffs are no match for the forces the sea exerts…Over time, the ocean always wins. In baseball terms, Mother Nature always bats last.

Read More

Sandbagging at the Shore: North Carolina’s Coastal Sand Bags and Political Sandbaggers; By William Neal, Orrin Pilkey & Norma Longo

April 1st, 2017

The wonder of modern English is how social use of language expands and changes the meaning of words. Sand bag is a bag filled with sand used for temporary construction—quickly made, easily transported, and easily removed. Typically, sandbagging is the emplacement of sand bags to construct a temporary protective wall or barrier, such as a dike or dam to hold back flood waters , or protection on the battlefield. But the term ‘sandbagging’ has taken on an array of other meanings…

Read More

Englands’ Jurassic Coast; By Gary Griggs

February 1st, 2017

In 2001, ninety-six miles of the south coast of England along the English Channel was designated as a World Heritage Site. This picturesque stretch of cliffs and beaches extends from Exmouth on the east to Studland Bay on the west.

Read More

Beach cusps: shoreline symmetry; By Gary Griggs

December 1st, 2016

There are many strikingly regular patterns in nature that have long intrigued scientists and non-scientists alike. Beach cusps are one of these.

Read More

Archive / Beach Of The Month