9. Textural and Facies Characteristics

Alluvial fans have no overall specific definable texture. Their clast size ranges from boulders to clay and shows a characteristic rapid downcurrent decrease in size. Close similarity in sediment texture from fan head to toe implies that no significant transport-related processes have taken place. Sorting improves down-fan but often remains moderate or still very poor. Normal grading results from a gradual decrease in the sediment supply or from waning flow velocities following floods. Inverse grading is often observed with stratigraphic thickening and corresponds to a prograding gravel front. The overall thickness of stratigraphic fans units ranges from several meters to a great thickness of a few kilometers. The thickest part of a fan usually leans against the mountain front.