Isobase maps

As mentioned elsewhere in the website, streams are a sensitive, first-order landscape feature, quick to respond to tectonic or climatic change. They also represent the local base level, as surface water collects in their channels and flows to lower regions.

Isobase, or "base-level" maps, effectively shed the less sensitive parts of topography- hillslopes and ridges- allowing you to see the exciting things happening to the structure of streams on a regional scale.

The main idea is to extract a stream network from a DEM, containing the primary, most incised channels (Generally the 1st and 2nd order streams from the Hack classification). Elevations are sampled every place these channels intersect major topo contours, and the result is re-interpolated via a spline or kriging model to produce a general surface constructed of benchmarks from major channels. Visually, this type of surface looks more generic than the true topography, with good reason! However, major trend-changes in isobase elevation contours can highlight the location of faults or other structures, and serve a useful purpose in displaying the potential tectonic regime for a region.