What is a coalescence cascade?

When droplets of water contact the surface of water, it doesn’t actually get absorbed straight away like you may think it does. What happens is it gradually bounces up and down until it is absorbed.

Underneath the droplet is a very thin layer of air, which allows it to sit temporarily above the surface. The air layer takes a bit of time to be pushed aside by the droplets weight. As the air moves from under the droplet, the surface of water pinches at water for a split second absorbing it. However it happens so fast that the connection is cut off between them and so a smaller droplet which hasn’t been absorbed bounces up.

As contact is made, waves are generated at the point of contact which surround the droplet, and go up the sides. This produces a force which allows the water droplet to leap up into the air. As it leaps up into the air, air fills the space underneath and the droplet once again sits on the thin layer of air. This process repeats until the mass of the droplet is so small it can just be absorbed by the water.

Watch more drops of liquid.

Thanks, Jethro and @Junephine.