Taking a chainsaw to an iceberg

Tuesday 7 July 2026

This summer, the University of Twente is melting two-metre blocks of ice in a large, water-filled silo on its campus. Researchers from the Physics of Fluids department are measuring how fast the ice melts in fresh and salt water to better understand the lifetime of icebergs.

It starts at a freezer container, which holds a two-metre rectangular block of ice. Using a pallet turner and a chainsaw, the researchers cut it into a clean cylinder. Every block is given the same shape, so the measurements can be compared. A crane then lowers the cylinder into the silo. The lid closes and the melting begins. Inside, underwater cameras record how the shape changes, while small particles in the water make the flow visible.

Warm and saline water

How fast a block of ice melts depends strongly on the salt in the water. And it works differently from what you might expect. In warm water, more salt makes the ice melt more slowly at first. Only at higher salinities does the melting speed up again. The cause is a tug-of-war between two flows. Cold (fresh) meltwater is light as compared to the saline environment and therefore rises. However, this rising meltwater cools down the ambient saline water, this then creates cold saline water which is heavier and sinks. At a certain salinity, the two flows roughly balance each other. That is when the ice melts most slowly.

The researchers saw this behaviour earlier with ice cylinders of thirty centimetres. Depending on the salinity, very different flows formed around the ice. At a certain ratio between heat and salt, wavy dimples appeared on the surface, a kind of scallop pattern, that slowly migrate downwards as the ice melts.

A step closer to reality

Strikingly, laboratory experiments and computer simulations showed almost the same thing. That agreement gives confidence that the researchers have captured the right physics. The work was published open access in the Journal of Fluid Mechanics. But thirty centimetres is small. Real icebergs are metres to hundreds of metres across. That is why the researchers are now scaling up to two-metre blocks, a step closer to reality.

“Climate models work on a scale of kilometres, but for the melting itself, the physics on a scale of metres is also very important. That small scale is exactly what we are trying to understand. Whether two metres of ice is large enough for the flow to fully develop remains the question. It will at least be a step in the right direction and the largest we can do in a well-controlled manner,” says researcher Simen Bootsma.

Faster than the models predict

Icebergs and glaciers are melting faster than many climate models predict. One important reason is that the physics of melting on a small scale, from metres to hundreds of metres, is not yet well captured in those models. That is exactly where these researchers are looking. The better they understand how ice melts in seawater, the sharper the predictions become for the lifespan of icebergs and for sea-level rise.