Final Answer:
Coastal plains can form in two basic ways:
(1) by starting as a continental shelf, a flat piece of land located below sea level, and when the ocean level falls, the land is exposed, creating a coastal plain;
(2) by developing when river currents carry rock, soil and other sedimentary material into the ocean, and layers of this deposited sediment build up over time, creating a flat or gently sloping landscape. Interior plains, on the other hand, are formed by the deposition of sediments from mountains on inland waters, forming rock layers upon layers.
Explanation:
Coastal plains can form in two basic ways. The first way is when a continental shelf, a flat piece of land located below sea level, is exposed when the ocean level falls, creating a coastal plain.
The second way is when river currents carry rock, soil and other sedimentary material into the ocean, and layers of this deposited sediment build up over time, creating a flat or gently sloping landscape. Interior plains, on the other hand, are formed by the deposition of sediments from mountains on inland waters, forming rock layers upon layers.