Imagine living on land that is barely above the ocean. Now imagine a giant wave of seawater heading for your home. That is the reality for millions of people in Bangladesh. On April 29, 1991, a powerful cyclone struck the coast. The storm pushed ocean water twenty feet high onto the shore. More than 138,000 people lost their lives. Bangladesh sits on the delta of two enormous rivers: the Ganges and the Brahmaputra. A delta forms when rivers dump sand and silt near the ocean. Over thousands of years, this builds up into flat land. Most of southern Bangladesh sits less than ten feet above sea level. When a storm pushes ocean water onto such flat terrain, there are no hills to block it. Bangladesh's location makes storms even more dangerous. The Bay of Bengal is shaped like a funnel. The narrowing coastline squeezes the water into a smaller space. This makes the storm surge grow taller and more powerful. After the 1991 disaster, Bangladesh built over 2,500 raised concrete shelters along the coast. The shelters sit on tall columns above flood level. When a similar cyclone struck in 2007, the death toll dropped by 97 percent. Geography made Bangladesh vulnerable, but smart planning saved lives.