Terminate upon icecap formation

island.ts

@@ -115,6 +115,8 @@ export function IslandApplet() {
   const basePos = len >> 1;
   const width = islands.width;
 
+  let timerId: number;
+
   function drop(pos: number) {
     const lowerNeighbors: number[] = [];
 
@@ -149,7 +151,10 @@ export function IslandApplet() {
     }
 
     // flat, increase elevation
-    islands.data[pos]++;
+    const newValue = ++islands.data[pos];
+    if (newValue == 9) {
+      clearInterval(timerId);
+    }
   }
 
   function tick() {
@@ -167,7 +172,7 @@ export function IslandApplet() {
 
   tick();
 
-  setInterval(tick, 1000 / 10);
+  timerId = setInterval(tick, 1000 / 30);
 
   return [canvas];
 }