A wall of ocean water 20 feet high can destroy everything in its path. On April 29, 1991, one of the strongest tropical cyclones in history struck Bangladesh. The storm had winds reaching 160 miles per hour. But the most destructive force was not the wind. It was the storm surge, a wall of ocean water pushed onto land by the cyclone. The surge reached 20 feet high in some areas. Bangladesh is especially vulnerable to cyclones. Much of the country is flat land only a few feet above sea level. The Bay of Bengal, where cyclones form, funnels storms directly toward the coast. Before the 1991 cyclone, Bangladesh had very few warning systems. Many people did not know the storm was coming. After the disaster, the country made major changes. Bangladesh built more than 2,500 concrete cyclone shelters on raised platforms. Each shelter can hold several hundred people. The government also created a network of 50,000 volunteers who spread storm warnings to villages. When a cyclone approaches today, these volunteers go door to door telling people to move to shelters. Scientists use satellites and weather stations to track cyclones days before they reach land. These improvements have saved tens of thousands of lives in later storms.