Figure 1. Generalized geological map of Mount Slamet, Central Java, Indonesia. Geological polygons and unit codes follow the BNPB Peta Geologi feature service. Elevation contours at 500 m intervals are derived from SRTM 1 Arc-Second Global. The inset locates Mount Slamet in Java. The map provides regional geological context; it does not delineate the summit features interpreted from the UAV surface in Figures 4 and 5.

Figure 2. UAV survey area and field acquisition at the Mount Slamet summit on 15 May 2025. (a) The red polygon is the reconstructed survey-planning area (3.99 km²), whereas the blue outline identifies the valid-data footprint of the delivered UAV raster (6.48 km²). These areas are distinct; the red polygon is not the computational simulation mask. UAV hillshade is displayed within the blue outline, with pale DEMNAS hillshade as regional context. The planning polygon was reconstructed from the supplied map. No measured flight tracks are shown because flight logs were unavailable. (b) UAV operation at the summit rim. (c) Field team and equipment. Projection: WGS 84 / UTM zone 49S (EPSG:32749).

Figure 3. Comparison of SRTM, DEMNAS, and the UAV surface elevation model. Panels (a–c) show the 6.48 km² valid-data footprint of the UAV raster within its 8.45 km² bounding rectangle; panels (d–f) enlarge the same 700 × 700 m window outlined in red. Extent within each row, elevation colour scale, and northwest illumination are held constant. SRTM and DEMNAS are masked to UAV coverage. Native pixel spacing is approximately 30 m, 8.29 m, and 0.530 m, respectively. SRTM is displayed from the prepared UTM raster used in the simulations. The comparison concerns spatial detail; vertical references and acquisition epochs were not harmonized.

Figure 4. Interpreted morphological features on the UAV hillshade: (A) steep crater-rim scarps and possible fissures, (B) an interpreted southwest-trending channel or putative pathway, and (C) the localized summit-low sector examined by profile C–C′. Markers identify representative locations, and the dashed line follows the interpreted channel axis. The channel has not been independently mapped or dated. The annotations do not establish fissure origin, a historical lava-flow age, or the closure and storage capacity of the summit low. Projection: WGS 84 / UTM zone 49S (EPSG:32749).

Figure 5. Matched 600 × 360 m hillshade windows and topographic sections for (A) the crater-rim sector, (B) the interpreted southwest-trending channel, and (C) the summit-low sector. Columns compare SRTM, DEMNAS, and the UAV surface with identical northwest illumination. Purple A–A′, B–B′, and C–C′ lines show the exact profile paths in every corresponding map; the dashed orange line is the interpreted channel axis, not profile B–B′. The lower curves use 1 m sample intervals, bilinear interpolation between the four surrounding native pixel centres, and a separate least-squares linear detrend for each product. No moving-average smoothing or interpolation across NoData gaps is applied. Profile endpoints are supplied in Supplementary File S1. Interpolation is solely for descriptive profile display and does not alter the simulation elevation grids. Vertical references and epochs are not harmonized; residual elevations describe local shape rather than absolute elevation accuracy.

Profile implementation. Existing profile paths have been retained. Sampling coordinates are transformed into fractional raster-centre indices by the inverse affine transform followed by a half-pixel offset. Elevation is the weighted mean of the four surrounding native pixel-centre elevations. A sample is retained only when all four contributing values are finite. Each product and path is linearly detrended by least squares against distance, using finite samples only. Curves have no moving-average or Gaussian filtering. The old extraction selected the containing native cell at 1 m intervals; after detrending and a short moving average, repeated 30 m values produced a sawtooth display. This pattern was an extraction/display artifact, not demonstrated fine relief or independent evidence of quantization in the original SRTM raster. Neither the new display interpolation nor the removed moving average was applied to the DEMs used for Q-LavHA.

Interpretive limitation. A detrended low in one cross-section does not demonstrate a closed depression, spill elevation, lava-storage volume, or physical flow stopping. Those claims require mapped closure and additional geometric or dynamical analysis. The revised figures therefore use 'summit-low sector' and avoid 'local trap'.

Descriptive channel metric. Profile B has two bracketing UAV shoulder maxima at distances −68 and +105 m, selected within the explicit left search band −120 to −40 m and right search band +60 to +130 m. At identical bracketing positions in each product, a straight line joins the two profile elevations; the maximum vertical deficit below that chord is 21.66 m for UAV (at +4 m), 4.92 m for DEMNAS (at +72 m), and 5.85 m for the corrected SRTM (at +22 m). Removing a linear trend leaves this chord-relative deficit unchanged. This metric describes product representation of the trough, not verified geomorphic depth, lava thickness, or storage capacity. The exact values and selection bands are retained in profile_B_chord_relief.csv.

Suggested comparative Results text. Along A–A′, all three products retain the broad rim envelope, but the UAV surface shows a sharper residual crest and abrupt variability east of the rim. Its detrended crest reaches 39.0 m at −33 m, compared with 30.8 m at −51 m in DEMNAS and 30.1 m at −21 m in SRTM. Along B–B′, the UAV surface resolves a pronounced trough between contrasting shoulders. The maximum deficit below a chord between the same two bracketing positions is 21.7 m in UAV, 4.9 m in DEMNAS, and 5.9 m in SRTM; the trough position also differs across products. C–C′ contains broad regional-product lows and much more irregular UAV elevations. The UAV residual range is 129.1 m, compared with 16.3 m in DEMNAS and 31.8 m in SRTM. These rapid UAV variations may include photogrammetric artifacts as well as real surface roughness, because no independent summit control is available. The profiles therefore demonstrate differences in represented surface geometry; they do not establish a closed lava-storage depression or validate the additional UAV detail.

SRTM registration. Figures 3 and 5 use work/minor-revision-2026-10-24/analysis/srtm_prepared.tif after correction of the HGT post-versus-edge registration. Figure 1 now interpolates the HGT posts at their exact coordinates (109 + column/3600, −7 − row/3600 degrees) to the figure bounds before contour extraction. The 500 m contours are derived with the actual longitude/latitude coordinates, without index stretching of a decimated crop.
