Forces and Orders of Relief

Forces Shaping the Earth

• Endogenic forces - internal forces - powered by Earth's internal heat engine - e.g., volcanism & faulting

• Exogenic forces - external forces - powered by insolation; energizes wind, water, and ice, and sets them in motion - includes processes of land denudation e.g., water, wind, and glacial erosion.

Exogenic Forces
Water Erosion Severe sheet erosion on  farm land Image courtesy NRCS	Wind Erosion Massive dust storm during the Dust Bowl era  Image courtesy USGS DDS21	Glacial Erosion Alpine glaciers are found on all continents today at high altitudes Image courtesy USGS DDS21

Orders of Earth Relief

• Relief: the elevations or inequalities of a land surface (Webster)

First Order Relief - Continents and Ocean Basins

• Crustal plates

Diagram Courtesy of USGS

Second Order Relief

• Created by plate tectonics; vertical and lateral motion of plates.

Divergent plate boundary (Mid-Oceanic ridge)

Diagram Courtesy of USGS

 

Convergent plate boundary

• Three types

  • Ocean - Continent (northwest coastal North America; Juan De Fuca - North America Plates)

  • Ocean - Ocean (Mariana Trench; Philippine - Pacific Plates)

  • Continent - Continent (Himalayan Mountains; Indian - Eurasian plates)

 

Diagram Courtesy of USGS

 

 

(Courtesy of USGS)

Ganges Plain is to the left and the  Tibetan Plateau  is to the right of the photograph (Courtesy of NASA)

 

Transform plate boundary (San Andreas Fault)

Diagram Courtesy of USGS

Second Order features of Continents

• Mountain systems (e.g. Rocky Mountains)

• Large depressions / Valleys (e.g. Great Rift Valley)

• Plateaus (e.g. Tibetan Plateau)

Second Order features of Oceans

• Ocean ridge system

• Trenches (e.g. Mariana)

• Plains (Abyssal plain)

Third Order Relief (Landforms)

• Produced mostly by erosion or deposition rather than tectonic movement.

• Individual Mountains or features (e.g. a mountain peak)

• Particular valleys (e.g., a river valley)

• No lower limit in size

Can you ...

• Describe the difference between first, second, and third order relief features?

• Describe the difference between convergent, divergent and transform plate boundaries? Where does one find these boundaries and what's occurring there?