On the volcanic Indian Ocean island of Anjouan, scientists are investigating a formation of quartzite, a rock apparently formed on a far-off continent. Its presence here defies conventional scientific theory. The island is part of the Comoros, a small, poor nation archipelago whose agricultural economy springs directly from its geologic history. (All photos: Kevin Krajick/Earth Institute) CLICK TO READ THE FULL SCIENTIFIC STORY
On a high ridge, a just-discovered outcrop of quartzite. An ancient rock, it could not have formed on this geologically young volcanic island; likely it started out within a riverbed or beach on a continent. Most of the formation may lie hidden below the surface. The researchers’ goal: map its extent and try to figure out how it got here.
All the rest of the island is made of blackish basalt, produced by a volcano that rose from the ocean floor. Cobbles of the rock line the shoreline.
The volcano that formed Anjouan has long been extinct; the interior has eroded into a maze of steep, heavily forested mountains and valleys. Despite its beauty, this is one of the world’s poorest, most isolated countries, where subsistence farming is the rule.
Quartzite is found only on a series of ridges above the rural hamlet of Tsembehou.
To reach areas where the rock might be found, the team must scramble up extreme slopes. With the island’s population booming and very little level land, even the steepest terrains are now planted with crops such as the banana trees here.
Team leader Cornelia Class (foreground) and geochemist Steven Goldstein scan a wall of basalt boulders for any unusual rocks.
This quartzite chunk was found lying loose on the ground within a garden, after just minutes of searching.
The scientists follow a bread-crumb trail of loose chunks, hoping to locate a larger mass from which they have eroded. Class and Comorian government scientist Bourhane Abderemane discuss where this one may have come from.
Goldstein inspects a cross section of lavas and volcanic ash deposits exposed in a road cut.
The work involves constant pounding on rocks to see what is inside.
Comorian government geologist Hamidi Soulé wields a 10-pound sledge hammer.
French geochemist Christophe Hemond takes a turn beating a quartzite boulder, trying to break off a sample. It didn’t work; the crystalline rock is extremely hard and resilient.
Abderemane searches a talus-covered slope for specimens.
A group of curious schoolboys tagged along on multiple days. The oldest repurposed a geologist’s hammer to open a coconut.
The researchers met a group of men digging out a hillside for a future mosque. In the exposed walls, the scientists found rare rocks from the deep earth, but no quartzite.
Another bunch of kids came to watch. On Anjouan, many women (and sometimes girls) routinely beautify their faces with a lotion made from the sandalwood tree.
Tsembehou resident Ali Saindou demonstrates a practical use for quartzite: sharpening knives.
Outside a garden, Goldstein discusses the project with (from left) Elhabioine Ameredine, his uncle Mourchidi Boura, and Elhabioine’s father.
On a strenuous uphill hike, the scientists discover an area that seems to be entirely underlain by quartzite. Someone has propped a couple of boulders of it under a tree.
Livingstone’s fruit bat is frequently seen flitting around at high elevations in daytime. Endemic to just two islands, its wingspan can reach three feet.
The Comoros are the world’s number one source of ylang ylang flowers, distilled to make the core of expensive perfumes. Unfortunately, not much money from this trade seems to filter back to most people here. Geologist Hamidi Soulé checks out a carefully pruned tree.
Cloves are another major export crop. They are everywhere along roadsides and in yards, drying fragrantly in the sun.
The port town of Mutsamudu is Anjouan’s capital and gateway to the outside world. Plagued by incessant poverty and political rivalries, the area around this street was the scene of an October 2018 anti-government uprising that killed an unknown number of people.
A cargo ship fires up. The islands have to import everything they can’t produce themselves. That includes Mideast oil, which fuels the on-again off-again electric grid.
A cultivated field overlooks the ocean. The constant decay of volcanic rock makes for fabulously rich soils, as well as natural beauty.
At an upland field within the scientists’ study area, cows vie for the remains of a jackfruit shared by a passing boy. Though Anjouan’s geology has helped people thrive, population growth may eventually outstrip the landscape.
Congratulations to our Columbia Climate School Class of 2026 and all of our 2026 Columbia University graduates! Learn more about our May 15 Climate School Class Day celebration. 💙 #Columbia2026 #ColumbiaClimate2026
This website uses cookies as well as similar tools and technologies to understand visitors’ experiences. By continuing to use this website, you consent to Columbia University’s usage of cookies and similar technologies, in accordance with the Columbia University Website Cookie Notice.
