diff --git a/src/sim/Planet.cpp b/src/sim/Planet.cpp
index 4da6b46..2aad852 100644
--- a/src/sim/Planet.cpp
+++ b/src/sim/Planet.cpp
@@ -54,6 +54,10 @@ void Planet::buildGeometry() {
     sHasBiota = false;
     sHumidity.clear(); sCloud.clear(); sRain.clear();   // weather spins up on entering Live World
     sHasWeather = false; sStorms.clear();
+    geoFeatures.clear(); sGeoRng = cfg.seed ? (cfg.seed ^ 0x6E0C12A7u) : 0x6E0C12A7u;
+    sCellLand.assign(cells.size(), -1); sCellWater.assign(cells.size(), -1);
+    sCellRange.assign(cells.size(), -1); sCellRiver.assign(cells.size(), -1);
+    volcanoes.clear(); sVolRng = cfg.seed ? (cfg.seed ^ 0x70C4F12Au) : 0x70C4F12Au;
 }
 
 void Planet::clearDerivedState() {
diff --git a/test_geography.cpp b/test_geography.cpp
index 4e9244e..c68d446 100644
--- a/test_geography.cpp
+++ b/test_geography.cpp
@@ -68,6 +68,26 @@ int main() {
     check(continents + islands >= 1, "at least one land mass");
     check(oceans >= 1, "at least one ocean");
 
+    std::printf("Geography: rebuild clears stale atlas state\n");
+    {
+        Planet r; r.generate(cfg); settle(r); drift(r, 40); r.generateGeography();
+        check(!r.geography().empty(), "regression setup builds an atlas");
+        Volcano stale{}; stale.cell = 0; r.volcanoes.push_back(stale);
+        PlanetConfig next = cfg; next.seed = cfg.seed + 1;
+        r.generate(next);
+        bool landEmpty = !r.cellLand().empty()
+            && std::all_of(r.cellLand().begin(), r.cellLand().end(), [](int v) { return v == -1; });
+        bool waterEmpty = !r.cellWater().empty()
+            && std::all_of(r.cellWater().begin(), r.cellWater().end(), [](int v) { return v == -1; });
+        bool rangeEmpty = !r.cellRange().empty()
+            && std::all_of(r.cellRange().begin(), r.cellRange().end(), [](int v) { return v == -1; });
+        bool riverEmpty = !r.cellRiver().empty()
+            && std::all_of(r.cellRiver().begin(), r.cellRiver().end(), [](int v) { return v == -1; });
+        check(!r.geographyBuilt() && r.geography().empty(), "generate() clears the old atlas");
+        check(landEmpty && waterEmpty && rangeEmpty && riverEmpty, "generate() resets per-cell feature indices");
+        check(r.volcanoes.empty(), "generate() clears stale volcanoes");
+    }
+
     std::printf("Geography: per-cell membership consistency\n");
     const auto& land = p.cellLand(); const auto& water = p.cellWater();
     const auto& range = p.cellRange();