am ▁and ▁sil ty ▁cl ay ▁lo am ▁text ures ." ▁ ▁Green ▁P ond ▁Marsh ▁and ▁kar st ▁ge ology ▁ ▁Green ▁P ond ▁Marsh ▁is ▁in ▁a ▁section ▁of ▁North am pton ▁County ▁with ▁kar st ▁ge ological ▁features . ▁Kar st ▁ge ology ▁manifest s ▁itself ▁on ▁top ographic ▁maps ▁with ▁closed , ▁semi - closed , ▁or ▁linear ▁de press ions . ▁The ▁de press ions ▁are ▁caused ▁by ▁the ▁d eter ior ation ▁of ▁the ▁under pin ning ▁lim estone ▁bed rock ▁by ▁ground ▁water . ▁In ▁many ▁cases ▁in ▁this ▁area , ▁sink hol es ▁occur ▁without ▁warning . ▁A ▁ 1 9 8 6 ▁study ▁by ▁W . E . ▁Koch an ov ▁of ▁the ▁Pennsylvania ▁Ge ological ▁Survey ▁showed ▁over ▁ 4 0 ▁symbols ▁representing ▁surface ▁de press ions ▁in ▁the ▁Green ▁P ond ▁Marsh ▁area . ▁ ▁A ▁search ▁of ▁the ▁Pennsylvania ▁Department ▁of ▁Conserv ation ▁and ▁Natural ▁Resources ' ▁online ▁map ▁vie wer , ▁when ▁switched ▁to ▁" ge ology " ▁view , ▁indicated ▁on ▁February ▁ 8 , ▁ 2 0 1 5 ▁that ▁there ▁were ▁ 1 3 ▁sink hol es ▁and ▁ 8 2 ▁surface ▁de press ions ▁within ▁a ▁one - half ▁mile ▁radius ▁of ▁the ▁clicked ▁marker . ▁ ▁In ▁a ▁ 2 0 0 5 ▁information ▁sheet ▁on ▁sink hol es , ▁the ▁Pennsylvania ▁Department ▁of ▁Environment al ▁Resources ▁states ▁ ▁that ▁"[ s ] ink hole ▁occurr ences ▁will ▁likely ▁become ▁more ▁frequent ▁as ▁population ▁enc