Using digital elevation models to calculate a time-averaged landscape denudation rate

Calculations of long-term, small-scale erosion rates based on the measureme nt of total eroded volume in a rock/soil unit have traditionally relied on poorly constrained, labor-intensive estimates of the removed volume. Digita l elevation models (DEMs), now widely available and relatively inexpensive, can be used as data sets to perform this calculation by computer. DEMs of hypothetical pre-erosional topographies need to be constructed for comparis on with the post-erosional topography. This requires field observation of c ontacts and subsequent geometrical calculations. This study's watershed, fo r which a long-term vertical erosion rate of 17 mm/ky was calculated, is fo rmed in Miocene rhyolitic ash-flow tuffs located in the Chiricahua Mountain s of southeastern Arizona. These welded tuffs are also known for their form ation of strikingly tall, slender erosional columns. On the basis of spacin gs of joints that control column formation, a horizontal erosion rate was a lso calculated. The combined erosion rates indicate that a typical column 5 0 m high would require approximately 2.9 x 10(6) years to form.