Icebergs frequently calve off Antarctica’s ice shelves, and they often get swept up in strong circumpolar currents that carry them around the icy continent. Occasionally icebergs drift northward, out of the continent’s orbit. Only rarely, however, do icebergs drift as far north as Australia without melting, which is why scientists were surprised to spot a city-sized iceberg, desginated B17-B, drifting toward Australia in December 2009.
Between early November and early December 2009, the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra and Aqua satellites observed the iceberg’s movement, shown in these true-color images. The top image shows the iceberg on November 5. The middle image shows the iceberg on November 29. The bottom image shows the iceberg on December 11. The iceberg’s contours change over time, and smaller icebergs splinter off from the main one, especially in the two later images.
The Associated Press and Agence France-Presse reported that the iceberg shrank from roughly 54 square miles (140 square kilometers) to 44 square miles (115 square kilometers) over the course of one week and then broke into hundreds of pieces, many several kilometers long. B17-B was spotted some 1,054 miles (1,700 kilometers) off the south-southwestern Australian coast in mid-December 2009. In November 2009, New Zealand issued a shipping alert about iceberg B17-B.
NASA Earth Observatory images created by Jesse Allen, using data provided courtesy of the University of Wisconsin’s Space Science and Engineering Center MODIS Direct Broadcast system. Caption by Michon Scott.