When ice flows over a jointed outcrop, it presses the joints shut on the upstream 
(ice; flows; over a jointed outcrop) (it; presses; the joints shut on the upstream; T:When ice flows over a jointed outcrop) (the joints; shut; L:on the upstream)
ice it the joints
flows presses shut
over a jointed outcrop
the joints shut on the upstream T:When ice flows over a jointed outcrop
L:on the upstream