INVESTIGATING A BALTIC SEA FOREDUNE FOR A HOLOCAUST MASS GRAVE USING GROUND PENETRATING RADAR IN ŠĶĒDE, LATVIA

Along the coastline of Šķēde, Latvia lies hidden mass graves from the Holocaust. The mass grave of interest (Grid 3) is ~100x4m, located behind a foredune (dune closest to the sea), and contains the bodies of 2,749 Jewish women and children who were murdered December 15-17, 1941. Each night before being sent to their deaths, Jews were confined to a building thought to be a barn (from historic testimonies). The investigation relied on current and past aerial imagery, witness testimonies, historical photos of the killings, previous research results, and GPR grids 1 and 2. To find the mass grave and reclaim it for the local Jewish community, ground penetrating radar (GPR), a non-invasive subsurface imaging technique was utilized. Grid 3 was 15x30m with lines collected every 0.25m using a pulseEKKOPro 500MHz antennae that allowed subsurface depths up to ~4m at 0.100m/ns velocity. A DJI aerial drone and historical imagery were employed to locate the remains of the building (~100m inland from Grid 3) and determine where Grid 1 should be laid. Based on results from Grid 1, Grid 3 was laid behind a section of foredune (~100m from the Baltic Sea) leading into woodland. Elevation was collected with a Topcon RL-H4C self-leveling laser and processed in Microsoft to calculate topographic values from cm to m. Data was then converted to .top files and attached to each grid line in EKKO_Project 6 software to geometrically correct GPR lines. Preliminary results indicate foredune disruption (a potential mass grave) starting at ~0.8-1m below the subsurface. The data is interpreted as disruption because the subsurface reflections (soil layers in the foredune) dip at the angle of repose (~30°), and soil layer breaks occur at ~17-21m along Grid 3. Comparatively, Grids 1 and 2 depict continuous dipping angles with no unnatural breaks. Imagery in Google Earth Pro from 2003-2024 suggests high progradation and erosion rates along the beach; the beach is currently ~90m to the foredune. High beach variability indicates the possibility for the potential mass grave and foredune to erode. The information gained will aid in protecting coastal foredunes from erosion to preserve the mass grave. The findings will also help the Liepaja Jewish community properly memorialize the site.