SPRINGS PHENOMENA AS CONTACTS BETWEEN NANGGULAN AND OLD ANDESITE FORMATIONS AT EASTERN WEST PROGO DOME, INDONESIA
Keywords:
Springs, gravity, contact, stratigraphy, faultAbstract
Nanggulan Formation located in the eastern part of Kulon Progo Dome that situated on weakly
undulated morphology with the elevation difference of 45 meters, the slope of 20.34%, and consisted of
impermeable clastics sedimentary rocks. The Old Andesite Formation that is surrounding reflected that the
steeply hills morphology with an elevation difference of 89.09 meters, the slope of 40.07%, and the permeable
volcanic rocks. Research area at the Kulon Progo Regency of D.I. Yogyakarta. Springs are generally rising in
between contact of Nanggulan Formation and Old Andesite Formation. These condition has become an
interesting problem to study further. The purpose of this research is to understand the presence of springs.
Whereas the aim of this research to determining morphology, lithology, and structural geology toward the
presence of the springs. The research methods used by field observation and gravity measurement. Gravity
method refered to the American Society for Testing and Materials Standard. The pattern of springs distribution
not always follow in valley lineaments. The result of gravity measurement showed that the presence of springs
around the Mujil traverse controlled by fault contact and stratigraphy contact. In contrast, of springs on the
Sentolo traverse was controlled by stratigraphy contact. Springs controlled by fault, followed by valley
lineament. The presence of springs due to stratigraphy contact occurred in contact with the permeable and
impermeable rock. The presence of spring due to stratigraphy contact could use as a preliminary indication of
the existence of contact of Nanggulan Formation and Old Andesite Formation.