Defying the laws of physics? Engineers demonstrate bubbles of sand

A recent discovery explains a new family of gravitational instabilities in granular particles of different densities that are driven by a gas-channeling mechanism not seen in fluids. The team observed an unexpected Rayleigh-Taylor (R-T)-like instability in which lighter grains rise through heavier grains in the form of 'fingers' and ''granular bubbles, similar to the bubbles that form and rise in lava lamps.

from Engineering News -- ScienceDaily http://bit.ly/2IMUbUJ