SPRINGS PHENOMENA AS CONTACTS BETWEEN NANGGULAN AND OLD ANDESITE FORMATIONS AT EASTERN WEST PROGO DOME, INDONESIA

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 theSentolo 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.