[pley-ney-shuh
n, pluh-] 
| the process whereby an irregular land surface is made flat or level by erosion. |
| pla·na·tion (plā-nā'shən) n. The process of erosion and deposition in which a nearly level surface is produced, as by streams, wind, or ocean currents. [Latin plānum, flat surface; see plane1 + -ation.] |