Abstract: In this paper, the shapes of blowouts were monitored using the high-resolution images of QuickBird in 2002, 2004 and 2009 and the field observation data. Though analyzing the shapes of three main types of blowouts including the mixed blowouts, trough-shaped blowouts and saucer-shaped blowouts, the different stages of shape variation were discussed from the view of geometric significance, and the shape evolution of three main types of blowouts was revealed. The results showed that the areas of the three types of blowouts were changed from enlargement to reduction from 2002-2004 to 2004-2009. From 2002 to 2009, the area of deflation basin was sustainably enlarged, and the depositional area was changed from enlargement to reduction. In terms of the area change of different types of blowouts, the areas of mixed and trough-shaped blowouts were sustainably reduced, but the area of saucer-shaped blowouts was enlarged at first and then reduced. From the overall shape of the blowouts, the shape change of mixed blowouts was the most noticeable, and then that of trough-shaped and saucer-shaped blowouts. Expansion of deflation basin occurred mainly in the eastern and southern marginal zones. From 2002 to 2010, the short-long axis ratio of the deflation basin changed differently, and there was a difference in geometric shape. The change of short-long axis ratio of mixed blowouts was slight, and the shape of deflation basin was remained basically.

Key words: sandy grassland, area, type, blowout, dynamic change, geometric measurement, Hulun Buir Grassland