The world's largest iceberg is on the move after being stuck to the ocean floor for 37 years. A23a stretches almost 1,500 square miles (3,885 sq. km) wide, or about three times the size of New York City and its five boroughs. The massive slab of ice weighs over one trillion tons and stands 1,313 feet (400 m) tall. For comparison, the Empire State Building measures 1,250 feet (380 m) from top to bottom.