1 / 18

Tectonics and Surface Relief

Tectonics and Surface Relief. Continents and Oceans. 71% of Earth's surface is below sea level. Sea level is a convenient reference, but doesn’t mark the boundary between oceanic and continental crust. Fig. 13.2. Continents and Oceans.

shanna
Download Presentation

Tectonics and Surface Relief

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Tectonics andSurface Relief

  2. Continents and Oceans • 71% of Earth's surface is below sea level. • Sea level is a convenient reference, but doesn’t mark the boundary between oceanic and continental crust. Fig. 13.2

  3. Continents and Oceans • Why is most continental crust above sea level and oceanic crust below sea level? • Answer: • The Principle of Isostasy – every part of the crust exerts an equal pressure on the underlying mantle. • Pressure = density  thickness  gravity.

  4. Basalt (oceanic crust): higher density, smaller volume Granite (cont. crust): lower density, larger volume Principle of Isostasy • Variations in density: • Each block exerts same pressure. Fig. 13.3

  5. Principle of Isostasy • Variations in thickness: • Each block has the same density. • Each block has the same percentage exposed and submerged. • Thickest block has "highest elevation" Fig. 13.4

  6. Principle of Isostasy • Continental crust: • less dense but much thicker • floats higher with deeper "roots" • Oceanic crust: • more dense, but much thinner • floats lower with shallow "roots" Fig. 13.6

  7. Fig. 13.10 Isostasy and Tectonics • What happens to continental crust at convergent plate margins? • The crust thickens but density is unchanged. • Increased thickness causes higher elevations and deeper roots.

  8. Fig. 13.11 Isostasy and Tectonics • What happens to mountains when they begin to erode? • As erosion removes mass from mountain tops, crust rebounds upward due to decreased pressure.

  9. Isostasy and Tectonics • Isostatic rebound explains why high grade meta. rocks are found at the surface. • As mountains erode, deep rocks are brought closer to the surface. Fig. 13.12

  10. Mountain Elevation and Age • Which mountain range is older, the Rockies or the Appalachians? Why? Fig. 13.23

  11. Isostasy and Tectonics • What happens to continental crust during continental rifting? • The crust thins but density is unchanged. • The crust subsides, causing lower elevations and shallower roots. Fig. 13.10

  12. Isostasy and Tectonics • What happens to continental crust during continental rifting? • Sediment eroded into rift valley. • Weight of sediment causes further subsidence. Fig. 13.10

  13. Isostasy and Glaciation • What happens to the crust when thousands of feet of ice are added? • Added mass causes subsidence. • Mantle flow causes slight uplift adjacent to ice. Fig. 13.13

  14. Isostasy and Glaciation • When the ice melts: • crust rebounds where ice was. • subsidence occurs in uplifted areas. Fig. 13.13

  15. Isostasy and Glaciation

  16. Relative Sea Level Changes • Presence of thick limestone deposits on the continents indicates that sea level has been much higher than today. Fig. 13.15

  17. Relative Sea Level Changes • Changes in water volume: • During glacial periods, water stored on continents, sea level lower. Fig. 13.15

  18. Relative Sea Level Changes • Changes in sea floor elevation: • Young, hot oceanic crust is less dense, floats higher on mantle, higher sea level. Fig. 13.15

More Related