Where weaker rock strata are exposed below more resistant rock, any of several erosion agents (gravity, streams, waves) can erode into weaker, basal rocks and undercut the more resistant rocks above.
(weaker rock strata; are exposed; L:below more resistant rock) (any of several erosion agents; undercut; the more resistant rocks above; T:Where weaker rock strata are exposed below more resistant rock)
weaker rock strata any of several erosion agents
are exposed undercut
L:below more resistant rock
the more resistant rocks above T:Where weaker rock strata are exposed below more resistant rock