Pressure Ridges
A new vent, a steeper slope, obstructions, increased flow -
many things change the pressure on lava flowing in a tube.
The pressure may heave up the crust and crack it, usually
along the crest.
The deeper cracks or crevices in the pressure ridges make
good homes for pikas, ground squirrels, and chipmunks.
Weasels hunt them there.
