|Tree foam looks like bubble bath.|
My Maryland hiking partner and I noticed this tree foam when we were hiking several years ago, and were unable to find an explanation. For a long time, I would ask everyone I hike with if they'd ever seen tree foam. I got a lot of blank stares. One hiking friend actually had seen it, and she calls it "tree spit"!
I finally found some literature about "stemflow" which provides a good scientific description of the process:
As I understand it, rain water dissolves stuff from the treebark as it flows down the stem of the tree. This changes the surface tension of the water, so that when it drips down towards the base of the tree, air is introduced due to the turbulence of the water, and foam is formed because of the altered surface tension.
Foam isn't just restricted to trees either. There is also "rock foam" and one time we even saw "trail foam" as the water was flowing downhill on a leaf-covered trail.
|Closeup of the bubbles|
|On every tree|