( ( The esker ) ( ( is ( ( a ( steep ( sided ridge ) ) ) ( formed ( when ( ( ( a tunnel ) ( within ( the ( ice sheet ) ) ) ) ( was ( filled ( with ( ( ( sand and ) gravel ) ( ( left behind ) ( by ( rushing meltwater ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NN esker)) (VP (VBZ is) (NP (NP (DT a) (JJ steep) (JJ sided) (NN ridge)) (VP (VBN formed) (SBAR (WHADVP (WRB when)) (S (NP (NP (DT a) (NN tunnel)) (PP (IN within) (NP (DT the) (NN ice) (NN sheet)))) (VP (VBD was) (VP (VBN filled) (PP (IN with) (NP (NP (NN sand) (CC and) (NN gravel)) (VP (VBN left) (PRT (RP behind)) (PP (IN by) (S (VP (VBG rushing) (NP (NN meltwater))))))))))))))) (. .)))
The esker is a steep sided ridge formed when a tunnel within the ice sheet was filled with sand and gravel left behind by rushing meltwater.
(ROOT (S (NP (DT A) (PRN (-LRB- -LRB-) (NP (NN n)) (-RRB- -RRB-)) (NN esker)) (VP (VBZ is) (NP (NP (DT a) (JJ winding) (NN ridge)) (PP (IN of) (NP (NN sand))) (SBAR (S (VP (VBD deposited) (PP (IN by) (NP (NP (DT a) (NN stream)) (PP (IN of) (NP (NP (NN meltwater)) (VP (VBN called))))))))))) (. .)))