Rates of stream incision in the middle part of the Arkansas River basin based on late Tertiary to mid-Pleistocene volcanic ash

Ages and elevations of ash layers correlated with late Tertiary and Pleistocene eruptions in the western US and present stream elevations are used to calculate net rates of incision by streams in the middle reaches of the Arkansas River basin in the south central US. The mean of the 23 measurements of rate of stream incision in the study area is 4.2±2.7 cm/ky with a range of 0.6 to 9.7 cm/ky. Major influences on rate of stream incision in the study area include the arid to semi-arid climate of the region, the type of material being incised by streams, stream captures, and salt dissolution in the bedrock that underlies the region. Rates of incision exceeded rates of basin filling but significant deposits of unconsolidated late Cenozoic sediments occur in the study area. Basins of streams that have incised the slowest since the late Tertiary contain the thickest and most extensive amounts of unconsolidated Quaternary sediments. Rates of incision by streams in the study area are similar to or slower than rates reported for streams elsewhere in the US and the world. Streams in mountainous regions and areas affected by rapid uplift have incised at rates orders of magnitude faster than streams in the study area.