CLASSIFICATION OF ALLUVIAL FANS IN TOHOKU DISTRICT BASED ON CLUSTER ANALYSIS

Alluvial fans in Tohoku District are classified into four types by cluster analysis based on 15 variables indicating their features and structures; namely, A-type (undissected largescale fans with thick deposits), B-type (dissected middle to small-scale fans with thick deposits), C-type (dissected fans with thin deposits), and D-type (undissected small-scale fans). In general, alluvial fans in Tohoku District are primarily classified by the thickness of alluvial fan deposits, and secondarily by the areal expansion of alluvial fan and the degree of dissection. Dissected alluvial fans with thick deposits are less distributed in the district. A lot of dissected alluvial fans with thin deposits are developed along the eastern foot of the Ou Range, while there are plenty of alluvial fans with thick deposits and undissected small-scale alluvial fans on the western foot of the range. These phenomena are expected to be explained based on the difference of the thickness of alluvial fan deposits.