A23a: Monster iceberg just shy of a trillion tonnes

The world's largest iceberg, A23a, has been accurately measured by scientists using satellite technology. The iceberg, which has an average thickness of approximately 280m (920ft), boasts an area of 3,900 sq km (1,500 sq miles), giving it a volume of roughly 1,100 cubic km and a mass just shy of a trillion tonnes. This colossal iceberg, which separated from the Antarctic coast in 1986, is currently drifting away from the White Continent.

Researchers indicate that the iceberg has reached a critical juncture in its journey. The trajectory it will follow through the Southern Ocean in the coming weeks will be determined by its current position. To provide some perspective on the iceberg's size, consider that the London skyscraper 22 Bishopsgate stands at 278m tall. However, A23a is more than double the area of Greater London, giving it a profile akin to that of a credit card.

The measurements of A23a were obtained from the European Space Agency's CryoSat-2 mission. This seasoned spacecraft is equipped with a radar altimeter that can detect the portion of an iceberg that is above the waterline. By using data on the density of ice, it is then possible to calculate the submerged portion. Dr Anne Braakmann-Folgmann, from the University of Tromsø - The Arctic University of Norway, explains that altimetry satellites like CryoSat-2 allow us to monitor iceberg thickness from space. They also enable us to observe the thinning of the iceberg as it is exposed to warmer ocean waters. With knowledge of the sea-floor topography, we can predict where an iceberg will ground or when it has thinned enough to be released again.