OVERVIEW

This chapter examines some of the major surface expressions of plate tectonic activity. These include landforms produced by volcanic activity and by the folding and faulting of crustal rocks, as well as earthquake activity.

• The surface forms of the earth's crust are known as landforms and the study of the processes which produce these features is called geomorphology.
• Initial landforms are formed by volcanic and tectonic activity while sequential landforms are formed by the agents of denudation such as running water, waves, wind and glacier ice.
• Lava eruptions at the earth's surface form volcanoes.
• Stratovolcanoes form from the eruption of thick, gassy, felsic lavas and are most common along the converging plate boundaries of the Pacific rim. They have steep sides and often have explosive eruptions that form calderas.
• Broadly rounded shield volcanoes form over hotspots and along midoceanic ridges where more fluid, less gassy basaltic lavas erupt. These lavas can form vast flood basalts when they erupt on continents.
• Tectonic movements can apply both compressional and extensional forces to rock.
• Compression along converging plate boundaries initially causes folding which produces anticlines and synclines. Sustained compression can lead to folds being overturned and to overthrust faulting.
• Extension along spreading boundaries generates normal faults with upthrown and downdropped blocks that can be as large as mountain ranges and rift valleys.
• Transcurrent faults occur where rock masses move horizontally past each other.
• Earthquakes occur when tectonic forces cause rock to suddenly fracture and move shaking the ground in the vicinity of the fracture.
• Submarine earthquakes can produce sea waves known as tsunami.
• The Richter scale is a logarithmic scale used to measure the energy released by an earthquake.
• Most severe earthquakes occur along tectonic plate boundaries.

KEY TERMS

landform           stratovolcano      normal fault       
geomorphology      shield volcano     transcurrent       
denudation         folding            fault              
volcano            fault              earthquake         
                                      tsunami            

STUDY QUESTIONS

1. Distinguish between initial and sequential landforms.
2. Define denudation and give three examples of denudation agents.
3. Discuss the way in which the internal earth processes and denudation processes interact to produce landforms.
4. Two major types of volcanoes are stratovolcanoes and shield volcanoes. How do these two types of volcanoes differ in their shape, material composition and usual position on lithospheric plates?
5. What is the difference between a hot spring and a geyser?
6. What are compressional and extensional tectonic activity and where do these usually occur?
7. Sketch a cross-section of an anticline, a syncline and an overturned fold.
8. Sketch a cross-section of a normal fault and a reverse fault. Label the fault plane, upthrown side, downthrown side and fault scarp on both cross-sections.
9. What is a transcurrent fault and what are some of the ways it might be expressed on the land surface?
10. Describe the global pattern of earthquake occurrence and discuss how this is related to plate tectonics.
11. Describe the cause and behavior of a tsunami.
12. How is the Richter used to characterize earthquakes?
13. Use the example of the Hawaiian island volcanoes to explain and illustrate the concept of a life cycle.