Code Loops Indefinitely

I am coding a procedural terrain generator for a project, but for some reason my nested for loops keep repeating indefinitely.

 using UnityEngine;
 using System.Collections;
 
 
 public class Terrain_Generator : MonoBehaviour 
 {
     public GameObject Target_Obj;
     public int width;
     int iteration;
     public int length;
     public int height;
     int prevPos;
     void Start () 
     {
 
     }
 
     // Update is called once per frame
     void Update () 
     {
         for (int j=0; j<width; j = j + 1) 
         {
             for (int i=0; i<length; i = i + 1) 
             {
             int horizPos = Random.Range (prevPos + height, prevPos - height * 2);
             Object.Instantiate (Target_Obj, new Vector3 (j, horizPos, i), Quaternion.identity);
             prevPos = horizPos;
             }
         }
     }
 }