( ( As ( ( the surface ) ( of ( the ( volcano ( changes shape ) ) ) ) ) ) ( , ( tiltmeters ( ( record ( ( ( ( ( ( ( tiny changes ) ( in slope ) ) , ) ( ( distances increase ) ( between ( benchmarks ( on ( ( opposite sides ) ( of ( the caldera ) ) ) ) ) ) ) ) , ) and ) ( elevations ( of ( the ( stations increase ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN As) (NP (NP (DT the) (NN surface)) (PP (IN of) (NP (DT the) (NN volcano) (NNS changes) (NN shape))))) (, ,) (NP (NNS tiltmeters)) (VP (VB record) (NP (NP (NP (JJ tiny) (NNS changes)) (PP (IN in) (NP (NN slope)))) (, ,) (NP (NP (JJ distances) (NN increase)) (PP (IN between) (NP (NP (NNS benchmarks)) (PP (IN on) (NP (NP (JJ opposite) (NNS sides)) (PP (IN of) (NP (DT the) (NN caldera)))))))) (, ,) (CC and) (NP (NP (NNS elevations)) (PP (IN of) (NP (DT the) (NNS stations) (NN increase)))))) (. .)))
As the surface of the volcano changes shape, tiltmeters record tiny changes in slope, distances increase between benchmarks on opposite sides of the caldera, and elevations of the stations increase.
(ROOT (S (NP (NNS Tiltmeters)) (VP (VBP are) (VP (VBN used) (S (VP (TO to) (VP (VB measure) (NP (NP (DT the) (NN angle)) (PP (IN of) (NP (NP (DT the) (NN slope)) (PP (IN of) (NP (DT a) (NN volcano))))))))))) (. .)))