QOM LAKE (DARYĀČA-ye QOM, or Qom Basin), also called Daryāča-ye Sāva, one of the interior watersheds in northwestern Persia (see DRAINAGE). It is situated between the southern flanks of the western Alborz system and the eastern slope of the northern Zagros, and covers just over 92,000 km². It forms the main part of a three-unit watershed system, the other two being the Daryāča-ye Ḥawż Solṭān and the Arāk Basin. It is also the lowest in the group, rising only 756 m above sea level. The basin itself is closer to the Alborz than to the Zagros Mountains, but receives most of its surface runoff from tributaries of the latter chain. Rainfall within the region in general is scarce and on average does not exceed 120 mm per year. However, winter rainfall and winter-spring runoff from the tributaries cause annual inundations forming a basin resembling an equilateral triangle stretching some 60 km on each side. In summer, the waters of the shallow lake evaporate rather quickly, leaving salt crusts which cover approximately two-thirds of the surface of the basin.
In form and physical features, the Daryāča-ye Qom is a textbook example of a typical playa in Persia. The basin is surrounded, primarily on the north, east and south, by a garland of mountain ridges, which are covered under very distinct aprons of debris, forming two piedmonts along the mountain frame, a degradational one in the upper sections and an aggardational one in the lower parts (see DAŠT; DESERT, Figure 2). The plain (dašt) areas then merge gradually in the desert (kavir) itself: in the western section, it is built up by a wet-zone; in the eastern section the dašt submerges directly under the salt-crusts.
A considerable sand dune field (erg) of almost 700 km² in size stretches to the south of the kavir. It very probably receives its sand material not from the playa, but from the alluvial plain between the city of Qom and the Daryāča-ye Qom.
Bibliography: see works cited in the bibliographies of DAŠT-E KAVIR and DAŠT-E LUT
Originally Published: July 20, 2002
Last Updated: July 20, 2002