3. Marangoni flow

Margoni flow arises when we have a free surface but the surface tension is not equal everywhere on the surface. Margoni flow goes from a point of lower surface tension to a point of higher surface tension.
For example, suppose we have a liquid with some powder sprinkled over it. We blow on the surface of the liquid thereby creating a hole in the powder layer. The surface tension at the point where there is no powder left will be higher than at the points where there is powder. So the liquid(with powder) will flow back to close the hole. This also shows us how surfactants tend to stabilize a flow.