According to the Direction Générale de la Sécurité Civile – Comores, the Observatoire Volcanologique du Karthala (OVK) reported that a significant increase in the number of small earthquakes beneath Karthala’s W flank began to be detected on 15 July. The abnormal activity persisted, so on 16 August the Alert Level was raised to Yellow (the second lowest level on a four-level scale) and residents were asked to limit activities on and around the volcano. On 5 September OVK recommended that the Alert Level remain at Yellow.

Geological Summary. The southernmost and largest of the two shield volcanoes forming Grand Comore Island (also known as Ngazidja Island), Karthala contains a 3 x 4 km summit caldera generated by repeated collapse. Elongated rift zones extend to the NNW and SE from the summit of the Hawaiian-style basaltic shield, which has an asymmetrical profile that is steeper to the S. The lower SE rift zone forms the Massif du Badjini, a peninsula at the SE tip of the island. Historical eruptions have modified the morphology of the compound, irregular summit caldera. More than twenty eruptions have been recorded since the 19th century from the summit caldera and vents on the N and S flanks. Many lava flows have reached the sea on both sides of the island. An 1860 lava flow from the summit caldera traveled ~13 km to the NW, reaching the W coast to the N of the capital city of Moroni.

Source: Direction Générale de la Sécurité Civile – Comores