Various links between landslide debris and sediment flux during earthquake and rainstorm events

Abstract

The variation of riverine dissolved ions is an important clue to understand the connection between earthquake and rainstorm-triggered landslide to the transference of sediment flux. The 2006 ML6.2 Taitung earthquake increased the annual sediment discharge of 27Mt in 2006; more than 2-fold the annual average 12Mt/yr of the preceding decade in the Luye catchment of southeastern Taiwan. During the same period of time, the proportion of area disturbed by landslides to total catchment area increased from 1.3% before to 2.3% after the earthquake. There was huge amount of vegetable delivered with the transport of landslide debris into channel to increase the concentrations of particulate organic carbon in water. However, those sediment flux produced from landslides in wet seasons usually included more particulate silicate material to dilute the occupied ratio of particulate carbon in sediment, which was lower in wet seasons but increased 4-fold in dry seasons. Besides, even through the variations of dissolved ions were relatively stable whether in wet or dry seasons because huge amount of fine material could be provided for whole year, we also found the concentrations of Na+, K+ and Mg+ had significantly increased during the rainstorms following the 2006 Taitung earthquake. This increase should still be attributed to the delivery of landslide debris into the channel, which had a positive impact on the sediment flux after earthquake and subsequent typhoon events.