Tectonic Geomorphology of Mountain Fronts

Abstract

Tectonic geomorphology of mountain fronts is that part of geomorphology concerned with processes and landforms near the junction of a piedmont and mountain front. Mountain fronts are generally segmented, and individual segments are evident from Google Earth imagery, processed LIDAR hillshades, aerial photographs from unmanned aerial vehicles (UAVs), vintage sources, and other media that image the landscape. There is typically significant change in relief from the piedmont through the mountain front zone and into the mountain range. That transition may be narrow and very abrupt, or it may consist of a zone several km or more in width that contains faults and folds on the piedmont and interior relic fronts. Many mountain fronts grow laterally as the faults that produce the front increase in length. Drainage is closely linked to mountain front tectonic processes formed by faulting. Drainage patterns, channel incision and aggradation evolve as range bounding structures change in length, height, and slope inclination with time. Mountain front segments can be characterized as being: geomorphically segmented, based on changes in surface morphology; structurally segmented where a front is produced directly by active folding and/or faulting; and segmented by historical earthquakes that coincide with rupture during an earthquake. A key to understanding what happens at a mountain front is to determine rates of processes. The study of mountain fronts includes: an examination of available imagery; application of geomorphic indices, particularly mountain front sinuosity and valley width and height ratios; fieldwork to verify what was learned from the imagery; development of the chronology necessary to assess rates of processes; and quantification of deformation of landforms along a front along with the application of the chronology to derive rates of uplift, deposition, erosion, and the geomorphic history.