The melting of glaciers across the globe began about 18,000 years ago, producing a rapid rise in sea level. The ocean was about 350 feet below its present level when the glaciers were at their maximum. Sea level rose about a centimeter (2.54 cm = I inch) per year for several thousand years. This rate of change was so fast that barrier islands could not develop. About 7,000 years ago the rate of sea-level rise slowed dramatically, and the first barrier islands began to form in the Gulf of Mexico on the Texas coast.