Karthala is the southernmost and larger of the two shield volcanoes forming Grand Comore Island (also known as Ngazidja).

Repeated episodes of collapse have led to a 3 x 4 km summit caldera.

Rift zones extend to the NNW and SE from the summit.

More than twenty eruptions have been recorded since the 19th century from both summit and flank vents.

These were mostly hawaiian is style with VEI's less than 2.

Stamp below courtesy of Lisa Heiman

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