Atolls, Anchor Watch, and Waves

4 Jul 2016 0 Share

Rangiroa from the air, Photo by Ben Thouard

Rangiroa from the air, Photo by Ben Thouard

COASTALWATCH | Pacific Climate Expedition

Situated in the Tuamotu Archipelago in French Polynesia, Rangiroa is the world’s second largest atoll. It’s our first stop here in the Tuamotu’s, “Land of the flat sky.” Lying about halfway between Argentina and Bundaberg, it’s surrounded by the vast Pacific Ocean, some of the most remote human settlement in the world.

We were lured here by that remoteness, and promise of incredible surf. One of the world’s last frontiers of deserted, perfect breaks. My most powerful impressions, however, are of being a long way from anywhere, and on our own in the face of the elements out here.

SEE ALSO: The Great Pacific Surf Climate Expedition

Just like surfers, sailors pay almost obsessive attention to wind and wave forecasts. Usually, we want the wind and don't want the waves. When it comes to anchoring, we don't want either. In Rangiroa, we’ve pressed right to the edge of our comfort zones managing the boat, safety and comfort due to the incredibly exposed nature of these atolls. Out here where massive Pacific weather systems converge between southern ocean lows and the standing high that creates the prevailing south-east trades that travel for thousands of miles from east to west.

An atoll is the leftover reef structure of a subsided volcanic island. Covering a vast stretch of ocean about 1200 miles long, The Tuamotu islands pushed up out of the ocean hundreds of thousands of years ago, as part of the Pacific “Ring of Fire”. They sprouted vibrant reefs encircling the islands, then slowly subsided, leaving only the barrier reef and massive lagoons within. The reef has been around so long it has built up a series of motus, or small islands, constructed singularly of broken down coral. These motus, stand one or two metres above sea level, and are only a few 100 metres wide between ocean and lagoon. They host little in both human and vegetable life, aside from the ubiquitous coconut palms and a few other varieties of trees. Beneath the surface of the water however, is an intense explosion of life and colour – from the coral gardens to the abundant fish, sharks and rays.

Rangiora measures approximately 30 nautical miles long, 20 miles wide and has a maximum depth within the lagoon of about 50 metres. In the southern part, the ring of reef sits just around water level, kept from growing higher by the work of relentless prevailing south-east swell and trade winds, which originate in the low pressure systems charging across the southern ocean. In the northern corner, motus have formed, protected by the moderating effect of the southern end of the atoll. Immediately outside, the sea floor plummets to 1300m then within a few miles drops quickly beyond 2000m. The atolls are coral topped pinnacles poking up from the profound depths of ocean.

SEE ALSO: Requiem For The Reef

Imagine, then, a collection of these atolls, in the face of ocean swell, current and winds that travel several thousands of miles to meet them, and what that might mean for the push of water, wind and waves in this part of the world.

As I write this, a massive trough along the east coast of Australia is pushing monster swell up along the coast, flooding homes and washing away famous parts of Sydney’s beaches and beach front buildings. Here in Rangiroa, four-metre swell from the south (related to the same low pressure systems creating havoc in Australia) is now crashing over the south end of the atoll, and, in combination strong SE winds, has filled the lagoon up like a big bath tub ready to over-flow.

The Passage, Photo by Ben Thouard

The Passage, Photo by Ben Thouard

Several nights ago we were woken by a change in the wind, and came on deck to observe an alarming fetch building from across the lagoon. With 20 miles behind the fetch, it quickly became a night of taking turns on watch, minding lines and observing other boats in the anchorage lest a mooring broke. The wind has swung more east now, relieving the boat anxiety, but the bathtub effect has prevailed. The water level is higher inside the lagoon than out, and there is a massive amount of push through the passes in order to equalize the levels between ocean and lagoon.

Passes in the reef are formed by ancient river mouths from an island long since lost beneath the sea. Coral couldn’t grow in the fresh water there, and the result is a channel of varying width but very short, through which must flow the tidal push and pull. In the conditions of the last few days, the inside of the lagoon is permanently trying to empty, thus there has been no incoming current in the pass for three days now, in spite of the normal tide action. Rangiroa has only two passes for a space measuring around 300 square miles, which makes for powerful action of water within the passes. Sailors and locals alike are gathering each day to observe the raging torrent – we estimate up to 10 knots of outgoing current – that is streaming through the pass, complete with 6-foot standing waves, tidal bores, circling maelstroms and angry looking peaks. All dives have been cancelled due to the danger of these conditions. At the local pier in town the water is sitting high on the concrete pier. The locals seem to be in acceptance and hunkering down for the stormy weather.

We are humbled, this is not like any of the anchorages or islands we have sailed before. The scope is so large, the forces are so great, and there is little or no topography to seek protection within. With no land height to shelter behind and no variation on the straight edged ring of reef, we feel we are clinging to the side of a long, inhospitable chain. For a sailor its high alert terrain, when most of your decisions are based around safety. What must it be like to live here? The locals at least have land, for the time being anyway.

Of course, the increased severity of weather with climate change will bring a very real threat to these atolls. The motus are under attack from the elements on both sides; I have seen rudimentary sea walls made out of coconut tree logs attempting to prevent the erosion from fetch across the lagoon. On the outside, the reef tends to be a hard coral shelf, but without any significant elevation to keep storm surge at bay it will provide very little barrier to extreme weather. A local woman spoke to us of the cyclones; rarer this far east but arriving with a vengeance when they do. “Where do you go?” we asked, contemplating the utter lack of high ground. To the church she replied. I wondered; was that because of its solid structure or to be closer to God as the only higher ground available?


Ruth Tedder is Captain of Blue Heeler 1, the vessel hosting the Pacific Climate Expedition. A sailing family’s journey through the South Pacific observing the effects of climate change on oceans health, people and places. The boat under the guidance of Ruth and her crew including husband Dr. Karl Mallon, two sons Django & Zoot and some experienced sea masters will be visiting some of the world's most remote surf breaks and posting footage as they travel and experience some epic waves, local music, and traditional culture.

This is the documentation from a crew of family, scientists, artists and students with a common love of the ocean and a wish to explore, contribute, collaborate and create new links.

Follow the crew along the way right here on Coastalwatch and on their Pacific Climate Exhibition Facebook page

Tags: Tuamotu Archipelago , French Polynesia , Rangiroa , ruth , tedder , climate , expedition (create Alert from these tags)

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