People are rearranging furniture in a crowded room. Sometimes a cabinet ends up against the wall and there's more space to move. Other times it gets shoved into a corner and the room feels even tighter. That's roughly how avalanches behave in a layer of grains that is slowly sheared, the way Earth's crust slides along a fault.

The researchers took about four thousand transparent disks and squeezed them between two fixed cylinders. A plate rotated slowly from below, while a weight pressed down from above. Under special light, the clear plastic reveals where the disks push against each other, so images were taken every 4 seconds. Microphones caught every click, and sensors measured the force on the walls. Over one hundred hours, roughly four hundred thousand acoustic bursts piled up.

Researchers used to think an avalanche always releases stress, like an exhale after holding your breath. But it turned out that the largest avalanches often do the opposite: the layer expands, and the pressure on the wall rises. These events were named negative avalanches. They barely move the grains, yet their faint displacements creep into an almost motionless region and blur the edge of the shear band. And they sound louder than ordinary ones.

So an avalanche may not free up room but lock stress in deeper, like a cabinet shoved into a corner. For earthquakes this matters: if a fault doesn't relax after one slip but instead charges up, predicting the next event becomes even harder.