iceberg

The last days of a giant iceberg

October 23, 2025 By EarthWise Leave a Comment

A colossal iceberg known as A-23A broke off from the Filchner Iceshelf in Antarctica in 1986. At that time, it was 1,418 square miles in area, slightly larger than the state of Rhode Island, or roughly twice the size of greater London. It weighed about a trillion tons. It was the largest iceberg ever observed.

After breaking off from the iceshelf, it lodged on the seafloor of the southern Weddell Sea for decades. It finally broke free in the early 2020s and began drifting northward. Last year, it got caught up in a rotating ocean vortex in the Drake Passage, and then became lodged on a shallow coastal shelf south of South Georgia Island. More recently, satellite imagery has shown A-23A to be on the move again.

Like other large icebergs that have found their way into the so-called “iceberg alley”, it is gradually succumbing to the effects of warmer air and water. Two large fragments of A-23A have already calved from it. These are huge in their own right: A-23G and A-23I are each over 125 square miles in area. The remaining main body of A-23A is still 580 square miles in area, making it the second largest freely floating iceberg in the world as of September. It had already lost much of its area since it began drifting north.

As it continues to drift northward, A-23A will continue to break apart. Many smaller pieces are littering the sea in its vicinity, but even these are large enough to threaten ships. The 40-year saga of iceberg A-23A is coming to an end.

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A Giant Iceberg’s Final Drift

Photo courtesy of the Earth Observatory at NASA.

Earth Wise is a production of WAMC Northeast Public Radio

The largest iceberg runs aground

April 10, 2025 By EarthWise Leave a Comment

The largest iceberg in the world, which has been slowly drifting for nearly 5 years, has finally come to a halt. The iceberg – called the unexciting name A-23A – came into existence in 1986 when it broke off from another iceberg A-23 that had calved or torn off from Antarctica earlier that year. For decades, A-23A sat in the Weddell Sea, east of the Antarctic Peninsula. Then, in 2020, it came loose from the seafloor and began to move. By 2023, it finally left Antarctic Waters.

Late last year, it began spinning in place caught in an ocean current called a Taylor column. Finally, it headed for South Georgia, a British-owned island that is home to a couple dozen people and lots of seals and penguins. A-23A is now stuck on the continental shelf, about 50 miles from the island.

A-23A is around 1,300 square miles in area. By comparison, New York City is 300 square miles.

Four years ago, a large iceberg called A-68A also came to ground in the vicinity of South Georgia. It quickly broke apart and ultimately added 150 billion metric tons of fresh water to the ocean as well as various nutrients. A-23A is also likely to succumb to the warmer waters, winds, and currents it now encounters and will affect the flora and fauna in the area.

The climate is changing and is impacting how ice shelves melt. Calving and the creation of mammoth icebergs are a normal part of the lifecycle of polar ice sheets, but we are likely to see even more events like this in the future.

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World’s Largest Iceberg Runs Aground

Photo, posted January 29, 2011, courtesy of Drew Avery via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

The end of a supergiant iceberg

November 16, 2023 By EarthWise Leave a Comment

In 2017, a supergiant iceberg known as A-68 calved from the Larsen C ice shelf in Antarctica. In 2020, it drifted close to South Georgia, a British island in the South Atlantic Ocean, and then began to break up. This iceberg was enormous – nearly the size of Delaware. When it started to break up, it released huge quantities of fresh, cold meltwater in a relatively small region.

Scientists from the British Antarctic Survey and the University of Sheffield have studied how the melting iceberg has affected the temperature and the salinity of the ocean surface in the area. They found that the water near the surface was 8 degrees Fahrenheit colder than normal and the water only had about two-thirds of its normal saltiness.

The effects from the melted iceberg eventually extended well beyond South Georgia as the colder, less-salty water was carried by ocean currents to form a long plume that stretched more than 600 miles across the South Atlantic. It also took several months to disappear.

The calving of this massive iceberg provided a unique opportunity for scientists to study the impact of iceberg melting on surface ocean conditions. A-68 was one of the largest and most studied of all icebergs. The study has shown that each individual melting giant iceberg can have widespread and long-lasting impacts on ocean conditions, which has consequences for the plant and animal life that lives there.

Climate change is likely to lead to more giant iceberg calving in the future. It is important to monitor these events to assess their future impacts on ocean circulation, biology, and even seafloor geology.

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Supergiant iceberg makes surrounding ocean surface colder and less salty

Photo, posted October 24, 2018, courtesy of Jefferson Beck / NASA via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Dangers Of Melting Glaciers | Earth Wise

March 31, 2023 By EarthWise Leave a Comment

Some of most dramatic evidence that the Earth’s climate is warming is the retreat and even disappearance of mountain glaciers around the world. 2022 was the 35th year in a row that glaciers tracked by the World Glacier Monitoring Service lost rather than gained ice. Glaciers gain mass through snowfall and lose mass through melting and sublimation (water evaporating directly from solid ice.) Some glaciers that terminate in lakes or the ocean lose mass through iceberg calving.

In the warming climate, glaciers retreat and meltwater collects at the front of the glacier forming a lake. Such lakes can suddenly burst and create a fast-flowing Glacier Lake Outburst Flood that can spread over a large distance from the original site – in some cases over 70 miles. These floods can damage property, infrastructure, and agricultural land and can also be deadly.

The number of glacial lakes has grown rapidly since 1990 as a result of climate change. According to research by an international team of scientists led by Newcastle University in the UK, the number of people living in glacial lake catchments has increased significantly.

According to the study, 15 million people live within 30 miles of a glacial lake. The highest danger is in High Mountain Asia – which encompasses the Tibetan Plateau. That area, which spans from Kyrgyzstan to parts of China, has 9.3 million people potentially at risk. India and Pakistan have around 5 million exposed people.

Detailed analysis shows that it is not the areas with the largest number or most rapidly growing lakes that are most dangerous. It is the number of people in proximity to the lakes and their ability to cope with potential floods.

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Glacial flooding threatens millions globally

Photo, posted February 12, 2022, courtesy of David Stanley via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

A Giant Breakaway Iceberg | Earth Wise

April 7, 2021 By EarthWise Leave a Comment

Scientists have been closely monitoring multiple cracks and chasms that have formed in the 500-foot-thick Brunt Ice Shelf in Antarctica over the past few years. In late 2019, a new crack was spotted in a portion of the shelf north of an area known as the McDonald Ice Rumples. The rift was monitored by satellite imaging and was seen by February as moving about 15 feet a day.

In the early hours of February 26th, the crack widened rapidly before finally breaking free from the rest of the floating ice shelf. News reports around the world have described the massive 500-square-mile iceberg by comparing it to the size of well-known cities: 1.5 times the size of greater Paris, 10 times the size of San Francisco, twice the size of Chicago, nearly the size of Greater London, and so on.

Antarctica is known for churning out some enormous bergs. The new iceberg, which has been named A-74, is huge, but doesn’t compare to the iceberg A-68 that calved from the Larson C Ice Shelf in 2017. That one was almost five times larger.

The calving of A-74 does not pose a threat to the presently unmanned British Antarctic Survey’s Halley VI Research Station, which was repositioned in 2017 to a more secure location after the ice shelf was deemed to be unsafe. The section where the station now sits is still holding on, but when it eventually breaks, it will likely create a berg nearly 700 square miles in size.

It remains to be seen what will become of the new iceberg. Most likely, it will eventually get caught up in the Weddell Gyre, a clockwise-rotating ocean flow in the Southern Ocean that covers an area more than half the size of the US.

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Breakup at Brunt

Photo, posted October 27, 2016, courtesy of NASA/Nathan Kurtz via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

A Trillion Ton Iceberg

July 24, 2017 By EarthWise

Back in February, we did a story about a rapidly-growing crack in the fourth-largest ice shelf in Antarctica. At that time, the crack in the Larsen C ice shelf was more than 100 miles long and was growing at a pace of about 5 football fields a day.

Cracking In The Antarctic

February 24, 2017 By EarthWise

A rapidly-growing crack in the fourth-largest ice shelf in Antarctica has scientists watching for it to break off entirely. By early February, the crack in the Larsen C ice shelf was more than 100 miles long and some parts of it were 2 miles wide. In the two-month period between December and February, the crack grew by 17 miles, a pace of about five football fields a day.