Journal of Geophysical Research: Earth Surface
© American Geophysical Union
Impact Factor: 3.426
ISI Journal Citation Reports © Ranking: 2014: 19/175 (Geosciences Multidisciplinary)
Online ISSN: 2169-9011
Associated Title(s): Journal of Geophysical Research
Earthquake-generated landslides are an important control of riverbed erosion
River erosion is a powerful shaper of topography, cutting through bedrock and over time converting smooth terrain to rolling hills or jagged cliffs. The rate of bedrock incision is influenced by the stream's slope and width, the water's flow rate, and the presence of sediment, among other factors. Researchers know sediment can play two conflicting roles: If the river's sediment load is low, it acts like sandpaper, increasing the rate of riverbed erosion. If there is plentiful sediment in the river, it forms a protective barrier along the riverbed, limiting erosion. What remains uncertain, however, is the influence of large, periodic inputs of sediment that enter rivers because of landslides or other extreme events. In 1999, the Chi-Chi earthquake in central Taiwan triggered thousands of landslides along the Peikang River, providing Yanites et al. (2011) with an opportunity to investigate the effect of a spike of sediment on long-term incision rates. The authors collected measurements of riverbed sediment depth at eight locations along the river, combining their results with previous records of long-term incision rates and morphological data. Using estimates of sediment flux, the researchers estimated the extent to which the riverbed bedrock is exposed and thus susceptible to erosion. They found that it could take decades or even centuries to flush the plug of sediment from the landslides out of the river system, trumping the influence of other river parameters. So while properties like flow rate and slope are important for the river's maximum potential erosion rate, the sediment's buffering capacity is a stronger determinant of long-term average rates.