Why this famous iceberg turned blue and what it tells us about melting ice
Recent satellite images indicate iceberg A-23A, one of the largest ever recorded, may split into smaller pieces in the coming weeks or months.
Iceberg A-23A as seen from the International Space Station. (Image: NASA)
NASA’s Earth Observatory captured striking new satellite imagery showing iceberg A-23A, once one of the largest icebergs ever tracked, which is now taking on an intense blue hue as it drifts in the South Atlantic Ocean.
This unusual color is not just a visual curiosity. It is a sign of widespread melting and structural weakening that could herald the iceberg’s final breakup.
According to NASA, under typical conditions, icebergs appear white because countless tiny air bubbles in the ice scatter all wavelengths of sunlight equally.
As A-23A has aged and melted, the conditions have changed. In 1986, when it first broke away from Antarctica, the berg was nearly twice the size of Rhode Island. Today, it's about 580 square miles.
On Dec. 26, 2025, NASA’s Terra satellite’s MODIS (Moderate Resolution Imaging Spectroradiometer) instrument revealed extensive pools of meltwater on the surface of A-23A. Earth scientists say these pools appear in deep shades of blue because water preferentially absorbs longer wavelengths of light (reds and yellows), while shorter blue wavelengths are scattered and reflected back to our eyes, similar to why the ocean and deep glacial ice can look blue.
The meltwater collects in depressions across the ice surface, forming ponds that can be several meters deep. The depth and clarity enhance the blue coloration, making it especially vivid in satellite imagery.
Why the meltwater is forming now
An image of iceberg A-23A in the South Atlantic Ocean taken on Dec. 26, 2025 by NASA's Terra satellite showing extensive pools of blue meltwater visible on its surface. (Image: NASA)
A-23A calved from Antarctica’s Filchner Ice Shelf in 1986 and has drifted for nearly four decades. Over time, it has slowly become smaller through natural fragmentation. But during the Southern Hemisphere’s recent summer, warmer weather and ocean waters accelerated surface melting, producing abundant meltwater.
The surface meltwater is pooling in fractures and low areas, painting the iceberg with blue streaks and patches that contrast against the remaining white ice.
What the color change reveals about the future of A-23A
An image captured on Sept. 11, 2025, by NASA's Terra Satellite shows the ongoing disintegration of Iceberg A-23A. (Image: NASA Earth Observatory)
The appearance of deep blue meltwater is also a bellwether of structural decline. Scientists note that the weight of water in cracks can pry the iceberg apart from within.
Imagery from both satellites and astronauts aboard the International Space Station suggests A-23A may be just days or weeks away from total breakup as it continues to drift into warmer seas.
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