evidence: Banc du Geyser is a mostly submerged reef in the northeastern part of the Mozambique Channel, 125 km (78 mi) northeast from Mayotte, 112 km (70 mi) southwest of the Glorioso Islands and 200 km (124 mi) off the northwestern coast of Madagascar. It is an oval-shaped reef 8 km (5 mi) long and 5 km (3 mi) wide that becomes exposed only at low tides, 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 sandy cays, 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 interesting underwater cave system accessible to divers. Banc du Geyser is home to a wide variety of marine life, including: