The fronts of glaciers in Antarctica that flow toward the coast break apart from melting, creating icebergs. These are known as birth events and can have dramatic consequences. Not only are large chunks of ice then free to move and reach lower latitudes, the process can also create powerful “internal tsunamis” that dramatically alter the ocean.
Internal tsunamis are a recent discovery. They are invisible in the sense that they do not create huge wavefronts, but can still displace a significant amount of water. They can exist in oceans and lakes without being noticeable on the surface.
The latest study was carried out by a team aboard the research vessel RRS James Clark Ross, part of the British Antarctic Survey (BAS) fleet. The scientists took ocean measurements near the William Glacier and witnessed the entire front shatter into a thousand pieces.
The front of the glacier was as high as 40 meters (131 feet) above sea level, and the amount of ice that broke covered an area of 78,000 square meters (840,000 square feet), or about 10 football fields. This may not seem like much, but it generated an internal tsunami with underwater waves as high as a house.
“This was remarkable to see, and we were lucky to be in the right place at the right time. Many glaciers end in the sea and their tips regularly split off into icebergs. This can cause large waves on the surface, but we know now it also creates waves in the ocean when they break these internal waves cause the sea to mix and this affects the life in the sea how warm it is at different depths and how much ice it can melt this is important for us to better understand,” study lead author Professor Michael Meredith, head of the Polar Oceans team at BAS, said in a statement.
Ocean mixing is an important process for the distribution of nutrients across the vast expanses of water. It was believed to be mainly caused by wind and tides, but this work suggests that iceberg calving that creates internal tsunamis also plays a role in the mixing. The team measured ocean temperatures and found that the tsunami had evened out temperatures at different depths.
“Our fortuitous timing shows how much more we need to learn about these remote environments and how they are important to our planet,” said Professor Meredith.
The study is published in the journal Science Advances.