Purwanto, Zufialdi Zakaria, Eko Teguh Paripurno, and Boy Yoseph C.S.S.S.A, “ANGLE OF SLOPE AND SLOPE SAFETY FACTOR RELATIONSHIP IN GENDOL RIVER, SOUTHERN SLOPE OF MERAPI VOLCANO, YOGYAKARTA”, INTERNATIONAL JOURNAL OF GEOMATE, vol. 17, no. 64, pp. 93–99, Dec. 2019.