Under the right conditions, sand can flow. When heavier grains are placed atop lighter grains in a container, the less dense grains can burble upward like the blobs of a lava lamp, a study finds.
The research is the first to show how the mixing of sand grains can mimic how fluids flow. But even when grainy particles, such as sand or mud, behave like fluids, the underlying forces that control how the grains move are different, researchers report online April 22 in the Proceedings of the National Academy of Sciences.
Understanding those forces could help scientists better explain the behavior of mudslides or of mixtures of hot gas and rock called pyroclastic flows from volcanoes. The research could also guide new technological designs for capturing carbon from the atmosphere or the production of pharmaceuticals.
Scientists had known that sand or other solid particles can behave like liquids under certain conditions. Strong earthquake vibrations, for example, can “liquefy” solid sand when it’s saturated with water. Less understood is how to mix grainy materials — from powders for pharmaceutical drugs to carbon dioxide-attracting beads — in the absence of water.