Geology Reports⌕ Search

SEARCH · Geology Reports

Results for “IMAP”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,423 records · Page 79Linked to original sources
USGS1991

Landforms of the conterminous United States — A digital shaded relief portrayal

Our map was made by digital image-processing, a technical specialty related to the broader fields of computer graphics and machine vision (Dawson, 1987; Kennie and McLaren, 1988). The technology includes the many spacially based operations first brought together and developed systematically to manipulate Ranger, Mariner, Landsat, and other images that are reassembled from spacecraft telemetry in a raster or scan-line arrangement of square-grid elements (Nathan, 1966; Castleman, 1979; Sheldon, 1987). These computer procedures have been successfully transferred to landform analysis from remote-sensing applications by substituting terrain heights or sea-floor depths for the customary values of electromagnetic radiation obtained from satellites an stored in digital arrays of pixels (Batson and others, 1975).

IMAP↗
USGS1993

Geologic map of the MTM 25057 and 25052 quadrangles, Kasei Valles region of Mars

Kasei Valles (fig. 1) make up the largest system of outflow channels on Mars and were a major contri butor of water to Chryse Planitia. The walls and floors of the Kasei channe ls are terraced and grooved , closely resembling the channeled scablands of easter n Washington State that were formed by catastrophic floods probably last ing no more than a few days (Baker and Milton, 1974; Baker and Kochel , 1979). Evidence obtained from previous geologic mapping of parts of Kasei Valles (Chapman and Scott , 1989) was n ot conclusive as to whether water levels varied markedly during single flood and erosional event or whether flooding was episodic and marked by intermittent periods of scouring . This problem – whether one or several flood episodes occurred within individual water courses – has been a continuing issue in studies of Martian channel formation (Greeley and others, 1977) . Recent large-scale geologic mapping (Tanaka and Chapman, 1990) of Mangala Valles, another large outflow channel system in the Memnonia region of Mars, shows deposits of two p eriods of flooding; the deposits are separated stratigraphically by a lava flow. In areas around the C h ryse basin, geologic studies ( for example, Greeley and others, 1977) indicate that more than one episode of channel formation occurred or, less likely, that flooding was of very long duration. Evidence disclosed by the present mapping indicates that flooding was episodic in Kasei Valles and probably occurred over protrac ted time intervals throughout the Hesperian Periods and possibly in the Early to Middle Amazonian.

IMAP↗