USGS Existing Landslide Areas (HESS)
United States Geological Survey (USGS) Existing Landslide Areas for development of the Parcel Inventory dataset for the Housing Element Site Selection (HESS) Pre-Screening Tool.
The best available predictor of where movement of slides and earth flows might occur is the distribution of past movements. These landslides can be recognized from their distinctive topographic shapes, which can persist in the landscape for thousands of years. Most of the landslides recognizable in this fashion range in size from a few acres to several square miles. Most show no evidence of recent movement and are not currently active. Some small proportion of them may become active in any one year, with movements concentrated within all or part of the landslide masses or around their edges.
This data provides a summary of the distribution of landslides evident in the landscape of the San Francisco Bay Region. Original identification and delineation of these landslides required detailed analysis of the topography by skilled geologists, a task generally accomplished through the study of aerial photographs. In general, landslide maps are now available for most of the region at scales of 1:24,000 - 1:62,500. The data modifies and improves the earlier compilations of landslide data, which was prepared from sources available in the mid-1970's. The generalized landslide distribution shown then has here been improved in areas where the 1970's sources were notably deficient and includes the distribution of surficial deposits that define landscape not generally vulnerable to these kinds of landslides. The method of compilation and resolution of 1:125,000 (1 inch = 2 miles) limits use of this data to regional considerations. For more detailed information, reference the original 1:24,000 - 1:62,500 maps, if available in local libraries, or consult local officials or private consultants.
A shapefile of the Existing Landslide Areas can be downloaded from here (https://mtc.maps.arcgis.com/home/item.html?id=6f8057505e844378813532969e43b826). A link to the ArcInfo (e00) source data is provided below.
FLATLANDS
Slides and earth flows do not occur on nearly flat ground -- they require slopes that are steep and long enough to permit failure. Thus this data excludes gently sloping ground from principal consideration. A slope boundary of 15 percent for this purpose. A similar criterion is the boundary between hillsides and areas of recent alluvial deposition. This boundary typically occurs at a slope of about 15 percent. This criterion has the advantage over slope alone of being limited to the lowland areas and excluding such other areas of low slope as hilltops and sidehill benches.
LANDSLIDE CATEGORY
The principal source of information used to define the distribution of slides and earth flows in the region is category 5 (landslides) of a 1979 regional slope stability map. The category 5 areas are a generalization of the distribution of mapped landslide deposits recognizable in the terrain, consisting principally of slumps, translational slides, and earth flows.
An important limitation of the earlier map is the varied character of the landslide mapping used in its compilation. For many areas, landslide inventory maps of various kinds, and even some detailed engineering geologic maps, were available, whereas elsewhere only general geologic maps were available. Some of the landslide inventory maps delineated only the most obvious landslides in the landscape, whereas others represented a thorough effort to identify all recognizable landslides.
From these varied sources, a generalization of the distribution of the landslides was determined by drawing envelopes around areas containing any type or size of mapped landslide that was within 1,000-1,500 feet of another landslide. Envelopes were also drawn around groups of landslides in such topographic settings as the same hillslope or creek bank, under the logic that such groups of landslides have a common local cause. Isol
Querying over HTTP
Splitgraph serves as an HTTP API that lets you run SQL queries directly on
this data to power Web applications. For example:
curl https://data.splitgraph.com/sql/query/ddn \
-H "Content-Type: application/json" \
-d@-<<EOF
{"sql": "
SELECT *
FROM \"bayareametro-gov/usgs-existing-landslide-areas-hess-25w2-bjdn\".\"usgs_existing_landslide_areas_hess\"
LIMIT 100
"}
EOFSee the Splitgraph documentation
for more information.
