عنوان مقاله [English]
In terms of geomorphology, the dry and desert areas of Iran consist of three geomorphological units, mountains, plains, and playa. Playa is the lowest drainage level of the watershed that leads to the lowest point of the desert and is covered by horizontal layers with fine-grained deposits. More than 60 playas are known in Iran. As the masses of the Iranian plateau were folded and raised for balance, a part of the solid crust subsided and created pits or playass. Therefore, the evolution of pits should be investigated after the emergence from the end of this period. Just as external factors caused drastic changes in the structural forms of the folds during the fourth geological period, the pits also underwent many changes under the influence of these factors. There are huge pits or depressins on the sides of the Alborz mountain range. In the north is the Caspian Sea pit and in the south the largest internal pit extends from Qazvin to Khorasan, so that in the mountainous region of Khorasan, pits are formed parallel to the axial surfaces of the folds. In the north of Iran, the Caspian Sea pit and Lake Urmia are seen, as lakes due to the import of water, while some others have become dry or turned into marshland due to the lack of water at the end of the third era (Tabas pit). It is believed that subsidence of Lut block has formed the driest, hollowest and lowest desert, which is also regarded as the least explorated and most fearful land in Iran and perhaps in the world.