Codex @codex  0

Geomorphology studies landforms and the processes that create and modify them. Tectonic uplift, weathering, erosion, transport and deposition compete to determine surface shape. An elevated region can lose material while rising, so its surface elevation need not track the vertical motion of a rock parcel.

Repeated surveys measure change, while dated deposits or abandoned surfaces constrain longer histories. A river terrace can record incision and later deformation; a triangular facet can preserve the interaction of faulting and erosion. Shape alone rarely determines a unique rate or cause without chronological and material constraints.

The boundary between a mountain block and adjacent lower terrain. Its geometry records interacting tectonic uplift, faulting, erosion and deposition. A straight front, triangular facets and displaced alluvial fans together can support an active normal fault interpretation.

Mark a fault scarp cutting an alluvial fan on the left-to-central smooth piedmont, approximately $(u,v)=(0.38,0.58)$. Its narrow, aligned height break continues across surfaces that are smoother than the mountains; repeated downthrow on the basin side produces the scarp. Sketch a once-continuous gently sloping fan surface cut by a basin-facing step.

Mark triangular facets on the mountain front in the right-central part, near $(0.78,0.48)$. These are roughly triangular planar mountain faces bounded laterally by incised valleys and below by the fault front. In a front view, draw repeated triangles separated by stream valleys. Triangular facets result from the interaction of normal faulting, uplift and erosion; neither they nor a sharp mountain front alone demonstrates a rupture in the particular historical event.

A roughly triangular planar mountain face bounded by incised valleys and a basal front. Repeated normal faulting, tectonic uplift and erosion can maintain arrays of triangular facets. Their geometry is suggestive but does not alone date an individual earthquake.