On extremely hot surfaces, droplets will skitter on a layer of their own vapor, thanks to the Leidenfrost effect. This keeps the liquid insulated from contact with the hot surface. But what if the surface isn’t solid?
That situation is what we see above. Instead of soaking into a granular material like a room temperature droplet (left), a drop falling onto a very hot bed of grains digs a hole! As with a typical drop on a super hot surface, the heat vaporizes part of the droplet. As the vapor escapes, it carries sand with it, allowing the boiling drop to burrow its way into the material. As the temperature difference between the sand and droplet changes, the digging slows. Eventually, the drop comes to a rest and boils away. (Video and image credit: J. Zou et al.)