11.2B Folds, Faults, and Mountains

1. 11.2B Folds, Faults, and Mountains Mountains, Plateaus, Domes and Basins

2. Types of Mountains • Folding and faulting produce many but not all of Earth’s mountains. • In general, mountains are classified by the processes that formed them • The major types of mountain types include • Volcanic mountains • Folded mountains • Fault-block mountains • Dome mountains

3. Mountain Ranges Types of Mountains : • Geologists refer to the collection of processes involved in mountain building as orogenesis.The term is derived from the Greek orosmeaning “mountain” and the –genymeaning “born”. • Earth’s mountains do not occur at random. Several mountains of similar shape, age, size and structure form a group called a mountain range.

4. Mountain Systems Types of Mountains : • A group of different mountain ranges in the same region form a mountain system. • The Sangre de Cristo and West Elk mountain ranges form part of the Rocky Mountain system. Sangre de Cristo Mountains Range Rocky Mountain System

5. Volcanic Mountains • Recall from the previous chapters that volcanic mountains form along plate boundaries and at hot spots. • In addition, igneous activity forms rock deep in the crust that can be uplifted as a result of plate motions and isostatic adjustment.

6. Folded Mountains • Mountains that are formed primarily by folding are called folded mountains. • Compressional stress is the major cause of folded mountains. • Compressional stress helped to form the Alps in Europe. • Thrust faulting is also important in the formation of folded mountains, which are often called fold-and-thrust belts.

7. Folded Mountains • Folded mountains often contain numerous stackedthrust faults that have displaced the folded rocks layers many kilometers horizontally. • The Appalachian Mountains, the northern Rocky Mountains, and the Alps in Europe are all examples of folded mountain ranges. Stacked thrust faults

8. Fault-Block Mountains • Fault block mountains; another type of mountain formation, is the result of movement along normal faults. • Most normal faults are small and have displacements of only a meter or so. • Others extend for tens of kilometers where they may outline the boundary of a mountain front. Examples fault block mountains

9. Fault-Block Mountains • Large scale normal faults are associated with fault-block mountains • Fault-block mountains form as large blocks of crust are uplifted and tilted along normal faults. Examples fault block mountains

10. Grabens and Horsts • Normal faulting occurs where tensional stresses cause the crust to be stretched or extended. • As the crust is stretched, a block called a graben, which is bounded by normal faults, drops down. • Grabens produce an elongated valley bordered by relatively uplifted structures called horsts.

11. Grabens and Horsts • The Basin and Range regions of Nevada, Utah, and California is made of elongated grabens. • Above the grabens, tilted fault-blocks or horsts produce parallel rows of fault-block mountains. Sierra Nevada Range

12. Grabens and Horsts • In the western US, other examples of fault block mountains include the Grand Tetons and the Sierra Nevada Range in California. • These steep mountain fronts were produced over 5 to 10 million years by many episodes of faulting. Sierra Nevada Range

13. Plateaus, domes, basins • Mountains are not the only landforms that result from forces in Earth’s crust. • Up and down movements of the crust can produce a variety of landforms, including • plateaus • domes • basins.

14. Plateaus • A plateau is a landform with a relatively high elevation and more or less level surface. • To form a plateau, a broad area of the crust is uplifted vertically; raised above the adjoining landscape. • Plateaus can cover very large areas of land such as the Colorado Plateau which stretches over four states. Colorado Plateau

15. Domes • Broad upwarping in the rock underlying an area may deform sedimentary layers. • When upwarping produces a roughly circular structure, the feature is called a dome. • Domes often have the shape of an elongated oval. • You can think of the upwarped layers that make up a dome as a large fold.

16. Basins • Downwarped structures that have a roughly circular shape are called basins. • The central United States contains a number of basins, including the large Michigan Basin. Michigan Basin

17. Basins • During mountain building, plate motions can cause the crust to bend downward and form a basin. • If the basin sinks below sea level, it may form a shallow sea. • Over time, sediments such as sand and the skeletons of ocean creatures are laid down, forming layers of sedimentary rock. Michigan Basin

18. Basins • Basins may also form along the edges of continents where thick layers of sediment build up. The weight of the sediment downwarps the crust to form a basin. • When forces in the crust uplift the sedimentary layers, the rock that fills the basin is exposed at the surface. Michigan Basin

19. Basins • Look at the map of the Michigan Basin to the right; it resembles a bull’s eye. The oldest rocks are around the edges of the basin and the youngest rocks are near the center. Michigan Basin

20. Basins • The plate motions that help to form sedimentary basins can also destroy them. • For example, when two continental plates collide, the ocean basin between them closes up. • Sedimentary rock in the basin becomes part of the landmass formed by the collision. Michigan Basin