Page 456 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

420 part III The Earth–Atmosphere Interface
to as a thrust fault. Horizontal movement along a fault plane, often producing a linear rift valley, is a strike-slip fault. The term horst is applied to upward-faulted blocks; graben refers to downward-faulted blocks. In the U.S. in- terior west, the Basin and Range Province is an example of aligned pairs of normal faults and a distinctive horst- and-graben landscape. A bolson is the slope-and-basin area between mountain ridges in this type of arid region.
folding (p. 390) anticline (p. 390) syncline (p. 390) faulting (p. 392) normal fault (p. 392) reverse fault (p. 393) thrust fault (p. 393) strike-slip fault (p. 394) horst (p. 394)
graben (p. 394)
Basin and Range Province (p. 394) bolson (p. 394)
6. Diagram a simple folded landscape in cross section, and identify the features created by the folded strata.
7. Define the four basic types of faults. How are faults related to earthquakes and seismic activity?
8. How did the Basin and Range Province evolve in the western United States? What other examples exist of this type of landscape?
■ List the three types of plate collisions associated with orogenesis, and identify specific examples of each.
Orogenesis is the birth of mountains. An orogeny is a mountain-building episode, occurring over millions of years, that thickens continental crust. It can occur through large-scale deformation and uplift of the crust. It also may include the capture and cementation of migrat- ing terranes to the continental margins and the intrusion of granitic magmas to form plutons.
Three types of tectonic activity cause mountain building along convergent plate margins. Oceanic plate– continental plate collisions are now occurring along the Pacific coast of the Americas, forming the Andes, the Sierra Madre of Central America, the Rockies, and other western mountains. Oceanic plate–oceanic plate collisions produce volcanic island arcs such as Japan, the Philippines, the Kurils, and portions of the Aleutians. The region around the Pacific contains expressions of each type of collision in the circum-Pacific belt, or the Ring of Fire. In a continental plate–continental plate collision, large masses of continen- tal crust, such as the Himalayan Range, are subjected to in- tense folding, overthrusting, faulting, and uplifting.
orogenesis (p. 394) circum-Pacific belt (p. 397) Ring of Fire (p. 397)
9. Define orogenesis. What is meant by the birth of mountain chains?
10. Name some significant orogenies.
11. Identify on a map several of Earth’s mountain chains.
What processes contributed to their development?
12. How are plate boundaries related to episodes of
mountain building? Explain how different types of plate boundaries produce differing orogenic epi- sodes and different landscapes.
■ Explain earthquake characteristics and measurement, describe earthquake fault mechanics, and discuss the status of earthquake forecasting.
An earthquake is the release of energy that occurs at the moment of fracture along a fault in the crust, producing seismic waves. Earthquakes generally occur along plate boundaries. Seismic motions are measured with a seis- mometer, also called a seismograph.
Scientists measure earthquake magnitude using the mo- ment magnitude (M) scale, a more precise and quantitative scale than the Richter scale, which was mainly an effective measure for small-magnitude quakes. The elastic-rebound theory describes the basic process of how a fault breaks, al- though the specific details are still under study. The small areas that are sticking points along a fault are points of high strain, known as asperities—when these sticking points break, they release the sides of the fault. When the elastic energy is released abruptly as the rock breaks, both sides of the fault return to a condition of less strain. Earthquake forecasting remains a major challenge for scientists.
earthquake (p. 401)
seismometer (p. 402)
Richter scale (p. 402)
moment magnitude (M) scale (p. 402) elastic-rebound theory (p. 404)
13. What is the relationship between an epicentre and the focus of an earthquake?
14. DifferentiateamongtheMercalli,momentmagnitude (M), and amplitude magnitude (Richter) scales. How are these used to describe an earthquake? Reference some recent quakes in your discussion.
15. How do the elastic-rebound theory and asperities help explain the nature of faulting? In your explana- tion, relate the concepts of stress (force) and strain (deformation) along a fault. How does this lead to rupture and earthquake?
16. Summarize what is known about the recurrence of high magnitude earthquakes off the coast of British Columbia and the Pacific Northwest.
17. Describe the San Andreas fault and its relation- ship to ancient seafloor spreading movements along transform faults.
18. How are paleoseismology and the seismic gap con- cept related to expected earthquake occurrences? 19. What do you see as the biggest barrier to effective
earthquake prediction?
■ Describe volcanic landforms, and distinguish between an effusive and an explosive volcanic eruption.
A volcano forms at the end of a central vent or pipe that rises from the asthenosphere through the crust. Eruptions produce lava (molten rock), gases, and pyroclastics (pulver- ized rock and clastic materials ejected violently during an eruption) that pass through the vent to openings and fis- sures at the surface and build volcanic landforms. Basaltic lava flows occur in two principal textures: aa, rough and sharp-edged lava, and pahoehoe, smooth, ropy folds of lava.
Landforms produced by volcanic activity include craters, or circular surface depressions, usually formed at the summit of a volcanic mountain; cinder cones, which are small conical-shaped hills; and calderas, large basin- shaped depressions sometimes caused by the collapse of a volcano’s summit.