Coastal & Marine Geology InfoBank

Home FACS Activities Atlas Geology School Related Sites More

USGS CMG InfoBank: Rivers and Valleys

Skip navigational links
Loading
Dictionaries: Our Mapping Systems   The USGS and Science Education   USGS Fact Sheets   Topics   Keywords   Data Dictionary   Metadata Dictionary   Computer Terminology   Digital Formats  
InfoBank Terms: Activity ID   activity overview   crew   digital data   formal metadata   lines   metadata   NGDC   port stops   project/theme   region   ship   stations   time   virtual globe   year  
Data Types: bathymetry   biological   geochemical   gravity   ground penetrating radar   imaging   LIDAR   logs   magnetics   metering equipment   navigation   samples   seismic   total station   definitions disclaimer  
Data Formats: ARC coverage   E00   FGDC metadata   gridded/image   imaging   material   scattered/swath   Shapefile   vector/polygon  
Comment: 02:48 - 03:46 (00:58)
Source: Annenberg/CPB Resources - Earth Revealed - 20. Running Water II: Landscape Evolution
Keywords: "Douglas D. Rhodes", river, valley, geologist, "mass wasting", sediment, stream, erosion, slope, "base level", degradation, "flow velocity", sea, "sea level"

Our transcription: The connection between a river and its deep wide valley is not an obvious one.
At one time, valleys were thought to have formed independently of the rivers which flow through them.
Today geologists are well aware that valleys usually form by the down-cutting of running water, combined with the mass wasting of slopes.
As a river cuts its channel deeper, it carries away sediment fed to it from surrounding hillsides.
Now there are limits to how deep that a stream can erode its valley, and those limits come up several kinds, which we generally refer to as "base level."
The ultimate base level, a grand base level is sea level.
Streams don't degrade their valleys below the level of the sea.
So we don't find great canyons arcing down to the ocean filled by water which is flowing back in from the sea.
The stream as it approaches the sea level loses velocity and, therefore, loses ability to erode.

Geology School Keywords
Skip footer navigational links

Coastal and Marine Science Centers:  Pacific   St. Petersburg   Woods Hole  
InfoBank   Coastal and Marine Geology Program   Geologic Information   Ask-A-Geologist   USGS Disclaimer  


Accessibility FOIA Privacy Policies and Notices

Take Pride in America logo USA.gov logo U.S. Department of the Interior | U.S. Geological Survey
URL: http://walrus.wr.usgs.gov/infobank/programs/html/school/moviepage/18.02.03.html
Page Contact Information: InfoBank staff
Page Last Modified: Thu Oct 31 04:28:06 PDT 2013  (chd)