( ( Such ( a glacier ) ) ( ( is ( called ( a ( rock glacier ) ) ) ) . ) )
(ROOT (S (NP (PDT Such) (DT a) (NN glacier)) (VP (VBZ is) (VP (VBN called) (NP (DT a) (NN rock) (NN glacier)))) (. .)))
Such a glacier is called a rock glacier.
(ROOT (S (NP (DT A) (NN glacier)) (VP (VBZ leaves) (PP (IN behind) (NP (JJ bare) (NN rock))) (SBAR (WHADVP (WRB when)) (S (NP (PRP it)) (VP (VBZ retreats))))) (. .)))
A glacier leaves behind bare rock when it retreats.