This is due to the fact that the islands barely rise above the sea, and thus can only support small communities of people. A toll Pass Atolls are the remains of steep, volcanic islands after hundreds of years of erosion and subsiding into the ocean floor. The Tuamotus were once cone-shaped peaks pushed up by volcanic activity. Throughout the ages, erosion and compacting of the rock wore away the volcanic peaks. At the same time, coral reefs built up around their bases.
Some passes are deep, and others are shallow.
Some, like the shallow pass pictured above, have water in them all the time, and some empty and fill with the tides. Atolls are low-lying and formed mostly from dead coral. Therefore, there is little topsoil suitable for growing plants. Coconut palms are abundant and provide food and livelihood for many Tuamotuans. Papayas, pictured above, were among the few fruits we found growing on the island.