If it wasn’t obvious to you before stay away from this area!
From Panda Bear, who took amazing images:
I was worried about this particular hole and how close it is to the old tunnel. Took a few shots illustrating what happened, the dirt from the hole washed away down the hill through holes in the retaining wall. Thankfully you can see where the dirt went and it doesn’t seem to have any connection to the tunnel. (Which I also checked on and seemed normal). As long as people stay away from it, I don’t think it poses any risk. More rain tonight could definitely see it grow.
See more of the images below: