Perbakti volcano is one of a complex of 3 closely located stratovolcanoes known as the Perbakti-Gagak or Kiaraberes-Gagak volcanic complex situated immediately SW of Salak volcano. The complex is hydrothermally very active. Fumaroles, warm spring and boiling mud pools are found on the S and SE sides of the volcano at 950-1300 m elevation. Mild phreatic eruptions took place in historical time from fumarole fields on its flanks.