UPDATE OF THE IDAHO GEOLOGICAL SURVEY LANDSLIDE INVENTORY

The Idaho Geological Survey (IGS) is updating the Idaho inventory of landslides. Preliminary work has consisted of three tasks: 1) evaluating the present inventory for accuracy and completeness; 2) updating the present inventory with new data from IGS geological mapping; and 3) refining database design and testing new tools for data distribution to the public. The present inventory (Adams and others, 1991) was designed to examine spatial patterns of landslide susceptibility and factors influencing slope failures. Problems include poor documentation of data sources, poor location precision (about 40 acres at best), and substantial numbers of inaccurately located records. Task 1 consisted of testing location accuracy and removing records with erroneous or ambiguous locations. Task 2 added landslides from 1:24,000-scale IGS geological maps published between 1993 and 2014. These data are mostly polygons showing landslide deposits and are biased toward large deep-seated failures. Task 3 is still underway and includes evaluation of databases and distribution tools from state and international sources.

Major landslides in Idaho highlight the importance of inventories in spotlighting regions of high susceptibility. Idaho highway and railroad networks have historically been subject to damaging landslides, many of which occurred in areas with documented landslide activity. Landslides impacting new subdivisions in landscapes with prior landslide activity are another source of losses. Finally, post-wildfire landslides are a growing concern in Idaho because of increasing fire severity and frequency.

Adams, W.C. and others, 1991, Landslides in Idaho: Idaho Geological Survey Surficial Geologic Map SGM-1, scale 1:500,000.