became a French overseas territory. In 1974, France organized a referendum for self-determination in the archipelago in which the population except in Mayotte voted overwhelmingly in favour of independence. Following the unilateral declaration of independence in 1975, France maintained sovereignty over Mayotte. The three remaining islands formed the Etat Comorian, which later became the Federal Islamic Republic of the Comoro Islands and is today the Union of the Comoros. In 1996, Ethiopian Airlines Flight 961 crashed off the shore of the grande island. 125 people died onboard, including the three hijackers who were the ones responsible for the crash. 50 people survived. In 1997, demands for increased autonomy on the islands of Ndzuani (Anjouan) and Mwali (Moheli) led to the breakup of the Federal Islamic Republic. In 2001, the government reformed as the Union of the Comoros under a new constitution which gave each of the three islands more autonomy than had been enjoyed previously. In 2008, the President of Anjouan refused to hold free elections. He was forced to flee following military intervention by troops of the Comorian Union and the African Union. The island country continues its present form of confederal government, albeit with minor changes approved in referendums in 2009 and 2018. Mayotte, which had voted to retain French suzerainty in the 1975 referendum, expressed a wish to accede to the status of a département d'outre-mer (DOM) (Overseas Department) following another referendum held on the island on the 29 March 2009. Mayotte officially became France's 101st department on 31 March 2011. Geology The Comoro Archipelago consists of volcanic islands. These volcanic islands, together with the high mountains in the north of Madagascar, were formed in the Tertiary and Quaternary periods. The island of Mayotte is the oldest one still above sea level and underwent three volcanic phases between 15 million and 500,000 years ago. The ages progressively decrease from east to west. Grande Comore is the youngest island and is still volcanically active. Karthala, a shield volcano occupying some two thirds of the island, rises to 2361 meters. The summit caldera is quite large, being approximately 3 x 4 km (1.9 x 2.5 miles) in size at the rim (2007). Climate The Comoro Archipelago enjoys a tropical maritime climate, characterized by slight daytime temperature variations throughout the year of around at sea level and by abundant precipitation: a year. The average temperature of the sea water is