Abstract: Based on the grain size data of near surface layer over four types of coastal dunes in Pingtan Island before and after the tenth Typhoon Matmo landed in 2014, such as coastal foredune, climbing dune and transverse dune as well as coastal sand sheet, the grain size change of near surface layer over four types of coastal dunes in response to the typhoon Matmo event is analyzed. The results suggest that the basic feature of the impact of typhoon Matmo on the grain size of near surface layer over four types of coastal dunes is the low change magnitude of grain size composition and grain size parameters after the typhoon Matmo landing compared with before, there is no clear change of grain size over coastal dunes resulted from the typhoon Matmo in observation sample areas, but the magnitude of grain size change differs between different type of coastal dunes and the sites over the coastal dunes although the change magnitude of grain size is very small. The basic factors influencing the characteristics of the typhoon Matmo impact on the grain size of near surface layer over four types of coastal dunes are the aeolian sands of coastal dunes and the beach sands in Pingtan Island have no significantly sedimentological discrimination in grain size composition and grain size parameters, and the high-speed wind under the condition of typhoon Matmo landing resulted in the strong wind erosion which eroded all the different grain size sands of near surface layer over four types of coastal dunes, meanwhile the special shape and the volume of coastal dunes also could influence the typhoon impact degree of grain size of near surface layer over four types of coastal dunes.

Key words: coastal dune, near surface layer, grain size, response to typhoon