The Great Catastrophe was an event that occurred prior to the Twelfth Doctor's visit to the Le Verrier station of the 38th century. It caused a tectonic realignment which resulted in India and Japan becoming merged and a new Indo-Japanese culture. (TV: Sleep No More)
Behind the scenes
After the airing of Sleep No More, writer Mark Gatiss confirmed that "The Great Catastrophe" was a reference to Frontios where the Earth had collided with the Sun.[1]