White Foam on Mature White Pine(s)
This looks like white pine sap (resin or pitch). We would need to see closer, in focus, photos to be able to say for sure. Sap will dry and look like white flaky, crusty patches.
We can't say for sure what has caused the sap to seep out. We don't see a lot of boring holes from insects or birds. It may be a stress indicator, but not necessarily.
We'd suggest to keep an eye on it. Notice if the branches put out normal new growth this spring or if there is dieback of branches. You can send us more photos of anything you see.
Here is a diagnostic chart for pines : http://extension.umd.edu/sites/extension.umd.edu/files/_docs/programs/hgic/HGIC_Pubs/TreesandShrubs/...
Again, the amount of sap in your photos doesn't necessarily indicate a problem.