The southern coast of Java, Indonesia, is situated along the active Sunda subduction margin where raised coastal landforms may record the combined influence of relative sea-level change, wave processes, sedimentation, and vertical land motion. This study presents field-based RTK-GNSS topographic profiles from four coastal sites: Pantai Ajah, Kalijali, Kulon Progo, and Wingko. Profiles were used to locate terrace treads, risers, slope breaks, residual topographic highs, and possible raised coastal surfaces. The results show spatially varying coastal morphology. Pantai Ajah has a marked riser and probable terrace tread at about 7–8.5 m elevation. Kalijali shows a lower terrace-like surface at about 4–5 m, an upper surface at about 7–9 m, and a higher local topographic high at about 12–13 m. Kulon Progo is characterized by a low-elevation coastal surface that is only weakly expressed in the topography, whereas Wingko contains a distinct slope break and a broad landward surface at approximately 5–6.5 m elevation. Across the four profiles, broad low-gradient surfaces recur within two elevation ranges, approximately 4–6.5 m and 7–9 m. These ranges are treated as provisional morphometric groupings rather than correlated or coeval terrace levels. Higher isolated elevations are described as ridge-like or residual topographic highs whose origin and age remain unresolved. No direct chronological or sedimentological constraints are currently available, so correlations with Holocene or older sea-level highstands are only tentative. The results show the usefulness of RTK-GNSS profiling for the documentation of local coastal terrace morphology and for the identification of priority sites for future dating, sedimentological analysis, and coastal-hazard assessment.

The southern coast of Java, Indonesia, lies along the active Sunda subduction margin, where coastal landforms record the interaction between sea-level change, wave erosion, sedimentation, and tectonic uplift. Marine terraces and raised coastal surfaces are important geomorphic indicators of vertical deformation, but their interpretation remains difficult where chronological control is limited and where coastal surfaces have been modified by erosion, deposition, karstification, or human activity. This study presents new Real-Time Kinematic Global Navigation Satellite System (RTK-GNSS) topographic profiles from four coastal sites: Pantai Ajah, Kalijali, Kulon Progo, and Wingko. The profiles were measured from the beachward side toward the landward side and were used to identify terrace treads, risers, slope breaks, residual topographic highs, and possible raised coastal platforms. These field data are integrated with published information on Holocene sea-level change, marine terraces, coastal uplift, and forearc deformation along the southern Java margin. The RTK profiles show variable terrace morphology between sites. Pantai Ajah preserves a prominent riser and a probable terrace tread at approximately 7–8.5 m elevation. Kalijali records a lower terrace-like surface at approximately 4–5 m, an upper surface at approximately 7–9 m, and a higher local topographic high near 12–13 m. Kulon Progo shows a subdued low-elevation raised coastal surface, while Wingko contains a distinct slope break at approximately 1450–1500 m from the beachward end and a broad landward surface at approximately 5–6.5 m elevation. The profiles suggest two tentative morphostratigraphic terrace groups: a lower group at approximately 4–6.5 m and an upper group at approximately 7–9 m. Higher local peaks, including the 12–13 m high at Kalijali and comparable elevated points at other sites, may represent remnants of older or more strongly uplifted coastal features. One possible interpretation is that some of these higher surfaces originated near the mid-Holocene sea-level highstand, when relative sea level in parts of Indonesia and Sundaland was higher than present, and were subsequently uplifted to different elevations according to local uplift rates. However, this hypothesis requires direct chronological and sedimentological confirmation. The raised terrace ridges and topographic highs may also act as partial natural barriers that reduce tsunami flow penetration inland, although they should not be treated as complete protection. Overall, RTK profiling provides a useful field method for recognizing coastal terrace morphology and identifying priority sites for future dating, tsunami-inundation modelling, and coastal-hazard planning.