The evolution of atolls seen from space
Atolls of French polynesia seen from space in March 2026.
20+ years ago, I fired up a flight simulator to fly over Tahiti and the islands of French Polynesia.
I was expecting turquoise water, lush islands and the usual postcard material. Instead, I was dismayed encountering a sight of dozens of white rings in the ocean with dark water in the middle. It looked like a common scenery bug at the time but little did I know.
Fortunately my geographical aptitude has somewhat improved since then. But it’s still true: From orbit, atolls look almost artificial with their perfect narrow rings and bright lagoons.
Today, we’ll leverage orbital imagery to explain step-by-step the formation of atolls by chaining together views of islands at different stages of this evolution.
Volcanic context and process
An atoll is a remnant volcanic island, meaning there needs to be a submarine volcano in the first place. In addition, the ocean has to support coral reef growth, or a ring never forms around the island. The South Pacific is where we look today, as most atolls are found there.
We cannot track the formation of a single atoll as the process takes millions of years and our satellite imagery is a few years short. So we tie together a chain of volcanic islands at different stages of their lifecycle.
Below image shows our examples and their volcanic context. Stages 1-3 where the islands are still emerging take place near active tectonic boundaries. Stages 4-6 where a stable island has formed and is becoming an atoll takes place farther away.
Tectonic plate boundaries and today’s target volcanic islands under study.
It is partly an accident the chosen island stages correlate so well with distance from plate boundary, as it is not always so clear cut in reality. But it illustrates that volcanic islands farther away from active plate boundaries are typically at later stages of their lifecycle.
Next, we take a closer look at the stages through the locations.
Stage 1 - Growing from the ocean floor
If orbital imagery could show the ocean floor, we would do just that because that’s where submarine volcanic islands start their way toward the surface. Luckily, submarine volcanoes make themselves known before emerging from the water by puffs or explosions of smoke.
Kavachi island is a highly active submarine volcano in the Solomon islands and a great example. Below is an image from December 27th 2025, showing the point-of-origin and the underwater smoke plume. In the imagery of Orbital Vantage, this is near the top of our favourite findings.
On some days, there can be no signs of a volcano visible or just a wisp, and at other times currents or the strength of the eruption colour a larger area.
Underwater eruption of Kavachi, Solomon Islands on December 27th 2025.
Stage 2 - A new island emerges
At some point, the volcanic material accumulates enough that it pierces the surface and becomes visible as an island. Below is an example of this: Hunga Tonga sometime in 2018 if I remember the scene date correctly. We see a growing island connecting two older volcanic peaks. The crater in the middle is clearly visible.
Hunga Tonga a few years before its famous eruption.
Stage 3 - A new islands collapses
The growth of a volcanic island is not stable. In January 2022, Hunga Tonga (same as previous image) violently reintroduced itself with one of the most powerful recorded volcanic eruptions, which was captured spectacularly by satellites. Funnily enough, the local geological service reported it dormant only 4 days before the massive explosion
Hunga Tonga in December 2022, roughly a month before the peak explosion.
Hunga Tonga now looks like below.
Hunga Tonga post-January 2022 explosion, with a rough outline of the island that disappeared.
Most volcanic islands go through this unstable phase and many never make it beyond it. The ones that do keep forming for millions of years before becoming an atoll.
Stage 4 - An island stabilises
Let’s move forward tens of thousands of years during which the volcanic island erodes, slopes soften and coral starts growing around it.
Here, something new starts appearing at the shoreline: A fringing reef. A good example is Rarotonga below. From orbit, we see a thin, bright turquoise outline hugging the coast. This is coral growth limited to shallow, sunlit water.
Rarotonga in a recent mosaic image, with clear fringing reef forming up.
The reef is still attached to the island and the volcano is in charge.
Stage 5 - The lagoon opens (barrier reef)
Fast-forward again. As the volcanic island slowly subsides and erodes, the reef keeps growing upward toward sunlight. The island and the reef start separating, forming a lagoon between.
We use Maupiti in Tahiti here as an example, west of the larger and more famous Bora Bora.
Maupiti and a barrier reef forming up around it.
From orbit, we see the volcanic core, bright lagoon and outer reef ring. But at this stage it is the reef that defines it, not the island.
Stage 6 - The island disappears (atoll)
Eventually, the volcanic island erodes and sinks below sea level entirely.
What remains is the reef. Now a ring of small islets called motu surround the lagoon. This entirety is what we call an atoll, Maldivian language meaning reef or a ring of coral islands.
The image coverage over the pacific is sparse, but we found a good example of Hikueru below. Seeing it for the first time would require a double take - the near-perfect circle is a very unique feature on Earth.
Hikueru atoll.
Why it matters: A balanced evolution
The interesting part is not just the evolutionary geometry, but that after the island formation, there are two separate processes that run in parallel and define whether an atoll forms over millions of years:
Reef growth: millimetres to centimetres per year
Island erosion and subsidence: Millimetres to centimetres per year
If the reef keeps pace, the system survives and transforms. Not every island finds this balance and follows the evolution to its completion.
Unfortunately, climate change is adding in athird paraller process - sea level rise - which both threatens the coral systems but also creates a stage where the atoll may end up prematurely submerged in just a hundred years.
The atoll formation stages in one image.
Conclusion
This was a good edge case that unfolded in the making: Atolls are not just a visual curiosity, but a volcanic island evolution that can be analysed stage-by-stage.
I wasn’t at first sure if I’m able to help explain the formation of atolls with orbital imagery, but it was easy to find islands at different stages after starting to think about the formation process. Orbital view does not show subsidence or reef growth in real time, but can reveal these structures when armed with knowledge of them.
See you,
Orbital Vantage
