Climate Change or Tectonic Shifts? The Mystery of the Sinking South Pacific Islands

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Environmentalist organizations have used images from South Pacific islands to illustrate the disastrous effects of rising sea levels. But a group of French researchers has found that the problem is much more complicated: The islands are also being pulled under by shifting tectonic plates.

Photo Gallery: Rising Seas or Sinking Islands? Photos
Gerald Traufetter / DER SPIEGEL

The island rises out of the ocean like a crenellated fortress. The trees on its slopes stand so close, their crowns so impenetrable, that the island appears to be wrapped in a blanket of green velvet.

Below, palm trees line the beach and the shapes of huts, some emitting smoke, stand out against the blinding light of the rising sun.

A team of French researchers steer their motorboat carefully through the reef toward Vanikoro, this fleck of earth that's part of the Solomon Islands, in the South Pacific. They've come here to uncover the island's secrets. "It feels is if we were on an expedition 250 years ago," says Valérie Ballu, 44, a geodesist from Paris. Geodesy is the science of measuring the Earth.

Ballu jumps into the shallow water of a sandbank, then pushes the boat ahead of her. The village on the shore is now showing signs of life. Women in brightly colored skirts appear at the entrances to their huts, babies in their arms. Naked, curious children with frizzy blonde hair run down to the edge of the beach, while men in dugout canoes paddle out to meet their foreign guests.

In less than a stone's throw, two cultures will meet, two different ways of living and thinking. Friendly laughter makes for a good start in easing this initial encounter.

"Momombo wako!" calls Alexandre François, 40, the French group's linguist. He has already lived on the island and studied its languages. The men from Vanikoro recognize him. They call him "the white man from the big island."

These foreign visitors are here because Vanikoro is slowly sinking into the ocean -- or at least that's what they believe. From their boat, the team begins unloading a number of heavy instruments with which they plan to measure the island.

Vanikoro has an area of less than 200 square kilometers (77 square miles), which makes it a bit smaller than Martha's Vineyard. Its 900 residents live without electricity, telephones or regular ferry service. The horizon gives off the impression of standing at the end of the world, and the only way to get away from this place is with a long pirogue, a dugout canoe outfitted with a sail.

The island's inhabitants divide Vanikoro roughly into three tribal areas, and they speak four different languages. Vanikoro lies more than 2,000 kilometers (1,200 miles) northeast of Australia and, like many of Oceania's islands, was created by volcanic activity, its destiny determined by the rubbing and colliding of continental plates. The researchers from France's National Center for Scientific Research (CNRS) plan to spend two days investigating this geological spectacle.

A Tiny Island with Global Significance

The first day begins with a disappointment: When Ballu and her team set out to find the location where they measured the island's elevation seven years ago, they discover that their most important survey marker, originally placed a safe distance from the beach, is now underwater, with the sea eroding the metal piece and its concrete base. "That's probably caused it to slide down," remarks geologist Stephane Calmant, 52, who fears this renders the marker "useless."

Still, this development offers proof of at least one thing: that the coast here is in motion. But the question remains: Is the sea level rising, or is the island sinking? "The questions we're trying to answer here on Vanikoro have global significance," Ballu says.

Indeed, since water levels are rising faster around the islands of the South Pacific than anywhere else on Earth, the region has become an important object of study for oceanographers, climate researchers and geologists. At the same time, it draws the attention of politicians and ecologists to these remote islands.

Not far south of Vanikoro, the island of Tegua is home to the people the United Nations declared the world's "first climate change refugees" in 2005. On Tegua, part of the island nation of Vanuatu, an entire village had to relocate due to rising water levels, and global media publicized photographs of a coconut plantation submerged in water, reclaimed by the sea.

That village relocation on Tegua "underlines the increasingly drastic measures now underway to conserve low-lying communities as a result of the rise in human-made emissions to the atmosphere," the United Nations Environment Programme (UNEP) warned at the time. Klaus Töpfer, a German politician with Chancellor Angela Merkel's center-right Christian Democratic Party (CDU) and the UNEP's executive director at the time, bleakly noted: "The melting and receding of sea ice and the rising of sea levels, storms surges and the like are the first manifestations of big changes underway which eventually will touch everyone on the planet."

A Battle for Every Millimeter

But does the fate of the village on Tegua really lend itself to being held up as a symptom of global warming? The researchers from France have their doubts, and they're here on Vanikoro to look for evidence.

Their first tool is a machete. Valérie Ballu is now looking for the second survey marker. Her colleague Alain Le Breüs pulls out hand-drawn sketches resembling a treasure map. But without even needing to look at the map, Alek Silo, a local, points a bony hand toward a young mango tree.

And, indeed, the researchers find their survey marker there under the bushes. They quickly unfold a yellow-and-red tripod of the kind land surveyors use. "Now the battle for every millimeter begins," Ballu says.

She checks the position of the GPS antenna, then asks Alek to cut down a couple of young trees that are interfering with reception. "We need signals from as many GPS satellites as possible for our measurements," Ballu explains. "That increases our accuracy." The display on her GPS device ultimately indicates contact with 16 satellites.

These devices will store position data from satellites every 30 seconds for 48 hours. "The longer we measure, the more precise the results," Ballu says.

Determining the minute motions of the Earth's crust down to the millimeter is no easy task. The planet is not a rigid sphere. Instead, it is constantly reshaped by the force of gravity exerted by the moon and sun as well as by other planets, such as Mars and Jupiter.

Those bodies tug not only at the Earth's surface, but also on the GPS satellites, creating discrepancies in their orbits. "All these things cause a loss of precision," Ballu explains.

The scientist climbs across two tree trunks spanning a boggy stream and heads back down to the beach. Calmant, the geologist, is pacing the beach with a GPS device in order to compare the results with previous sketches. Le Breüs points to tree roots rotting in the water and says: "On my first visit, the coast ran along behind there."

Le Breüs has been to Vanikoro several times, but his previous visits were for a different reason. "We're standing on historical ground," he says, pointing out a memorial stone bearing a bronze plaque. This beach, he explains, is where explorer Jean-François de Lapérouse's courageous crew of sailors took refuge when their ships sank on the reef surrounding the island.

The two ships set sail shortly before the French Revolution, dispatched by France's beleaguered regent, Louis XVI. In 1788, they had been at sea in the Pacific for two years when Lapérouse, ill with scurvy, found himself in the middle of a cyclone. "By the time the men spotted the island in the frothing sea, it was too late," Le Breüs says. "They were already too close to the reef."

The fate of Lapérouse's men captivated all of Europe in the early 19th century, and the shipwreck earned the small island of Vanikoro a mention in world literature. "Ah, what a splendid death for a seaman!" exclaims Captain Nemo, the hero of Jules Verne's 1870 novel "20,000 Leagues Under the Sea," when he dives down to the wreck.

Le Breüs was there when archeologists came and salvaged anchors and glasses. On the beach, they found coins, chinaware and a skull they were able to identify as belonging to a scientist who had been aboard the ship. Now a GPS device stands at the site of that tragedy, recording data.

A climate-change report to be published next year will present evidence that the world's oceans will rise between 0.5 and 1.2 meters (1.5 and four feet) by 2100, with global warming already increasing sea levels by 1.8 millimeters (0.07 inches) a year. However, that amount is not much when compared to the natural fluctuations at work here. Like most inhabitants of the South Pacific, those of Vanikoro must contend with sea-level fluctuations of some 20 centimeters (eight inches) caused by currents in the Pacific, such as the climate phenomenon called El Niño.

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1. Sea Level Rise
DouglasM 06/15/2012
Definitely tectonic shifts, according to Holgate, a recognised world authority in geophysical research at the UK-based Proudman Oceanographic Laboratory in Liverpool, in his paper published in 2007, the following results represent the most comprehensive measurements of decadal sea-level change rates during the 20th century. Between 1904 and 1953 global sea levels rose by 2.03 mm per year, whereas from 1954 to 2003 they rose by only 1.45 mm per year, giving an annual mean rate of 1.74 mm per year over the 100 years to 2003, or seven inches per century. Importantly, there was no increase in the rate of change over the whole century.
2. Sinking Islands
richard.guy.9828 09/25/2014
All the Pacific Islands are subject to tectonic forces on the ocean floor. Speak to any ntive islander and he will tell you that islands pop up and down over time. They pop up as Volcanoes and disappear as tectonics dictate. If you look at the ocean floor maps you will see clearly that al these atoll Islands perch precariously on top of undersea plates which are constantly on the move. These plates are not as well defined as the Mid Atlantic Ridge but they are active and restless. The Islands ride on these plates and either pop up or sink.
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Graphic: Tectonic shifts in the South Pacific. Zoom
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Graphic: Tectonic shifts in the South Pacific.


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