Formation Mechanisms and Geomorphic Evolution of the Erlian Mudflow Fans, Eastern Guide Basin of the Upper Reaches of Yellow River

Several argillaceous platforms lie along the Yellow River (YR) of the eastern Guide Basin, northeastern Tibetan Plateau, and their compositions, formation processes, and geomorphic evolution remain debated. Using field survey data, sample testing, and high-resolution remote sensing images, the evolution of the Erlian mudflow fans are analyzed. The data show significant differences between fans on either side of the YR. On the right bank, fans are dilute debris flows consisting of sand and gravel. On the left bank, fans are viscosity mudflows consisting of red clay. The composition and formation processes of the left bank platforms indicate a rainfall-induced pluvial landscape. Fan evolution can be divided into two stages: early-stage fans pre-date 16 kaB.P., and formed during the last deglaciation; late-stage fans post-date 8 kaB.P. Both stages were induced by climate change. The data indicate that during the Last Glacial Maximum, the northeastern Tibetan Plateau experienced a cold and humid climate characterized by high rainfall. From 16-8 ka, the YR cut through the Erlian early mudflow fan, resulting in extensive erosion. Since 8 ka, the river channel has migrated south by at least 1.25 km, and late stage mudflow fan formation has occurred.