The world's biggest iceberg, A23a, which was around 3,500 sq km has disappeared after drifting through the Antarctic Ocean for around 40 years. It travelled more than 2,000 km in the Antarctic Ocean before entering warmer waters where it gradually melted. A23a was one of three icebergs that were formed after breaking away from Antarctica's Filchner–Ronne Ice Shelf in 1986.