Banc du Geyser (alsoBanc du Geysir) is a mostly submergedreef in theMozambique Channel's northeastern part, 125 km (78 mi) northeast fromMayotte, 112 km (70 mi) southwest of theGlorioso Islands and 200 km (124 mi) off the northwestern coast ofMadagascar.

Banc du Geyser

Disputed reef
Satellite image of Banc du Geyser (center) withMayotte (left), theGlorioso Islands (top right) andMadagascar (bottom right)
Banc du Geyser
Other names	Banc du Geysir,Arecife de Santo Antonio
Geography
Location	Mozambique Channel
Coordinates	12°19′12″S46°27′00″E / 12.32000°S 46.45000°E /-12.32000; 46.45000
Archipelago	Comoro Islands
Length	8 km (5 mi)(low tide only)
Width	5 km (3.1 mi)(low tide only)
Highest elevation	8 m (26 ft)
Highest point	South Rock
Administration
France
Claimed by
Comoros
Madagascar
Demographics
Population	0

The Banc is a dangerous oval-shaped reef 8 km (5 mi) long and 5 km (3 mi) wide that becomes exposed only at lowtides, with the exception of some rock formations in the southern part of the reef. The rocks are generally 1.5 to 3 m (5 to 10 ft) in height; the largest is South Rock, with a height of 8 m (26 ft), similar to a boat under sail.

In the eastern part of the reef there are some sandycays, 1 to 3 m (3 to 10 ft) in height covered with grass and small bushes. The entrance into the central lagoon is possible from a south-southeastern direction. There is an abundance ofseabirds, and the cays are covered in tons ofguano.

About 20 km (12 mi) southwest of Geysir is Zélée Bank, a deep submarine feature.

The Geysir Reef was first known by Arab sailors around the year 700, and was shown on some navigation-charts dated around 800. Around 1650 the reef was shown on Spanish maps asArecife de Santo Antonio. The current name was given on 23 December 1678, when a British vessel, Geysir, ran on the reef.

France and theComoros claim the Banc du Geyser as part of theirexclusive economic zone (EEZ). The reef is also claimed byMadagascar. From the French point of view, it is a part of the EEZ ofGlorioso Islands, one of theirScattered Islands in the Indian Ocean. Madagascar announced its annexation in 1976, presumably because of the possibility ofoil fields in the vicinity but the Banc du Geyser is controlled in fact by the Frenchforces armées de la zone sud de l'océan Indien.

In 2012, France included the reef in theparc naturel marin des Glorieuses, amarine protected area, to preserve the endangered flora and fauna of theGlorioso Islands.

• "Satellite images of Banc du Geysir". Archived from the original on 23 December 2010. Retrieved14 March 2009.
• Sailing Directions: East Africa and the South Indian Ocean. Accessed 30 September 2022.