1. Chapter 9 Volcanic and Tectonic Landforms
Visualizing Physical Geography by Alan Strahler and Zeeya Merali
Chapter 9 Volcanic and Tectonic Landforms
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

2. Volcanic Landforms
Continental landforms are the result of endogenic and exogenic processes.
Endogenic process: works from within the Earth
Produces initial landforms
Uplifts; brings fresh rock to the surface
Powered by Earth’s internal energy
Exogenic process: works at Earth’s surface
Wears down initial landforms
Creates sequential landforms
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

3. Volcanic Landforms
Volcanic Activity Volcano: conical, circular structure built by accumulation of lava flows and tephra (volcanic ash)
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

4. Many volcanoes are located on subduction boundaries or rift zones.
Volcanic Landforms
Volcanic Activity
Many volcanoes are located on subduction boundaries or rift zones.
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

5. Volcanic Landforms Stratovolcanoes
The nature of an eruption depends on the type of magma involved.
Felsic lavas associated with stratovolcanoes
Rhyolite, andesite
Thick, resistant to flow
Builds steep slopes around volcanic vents
Tall, steep cone, with crater
Stratovolcano: volcano constructed of multiple layers of lava and tephra (volcanic ash)
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

6. Volcanic Landforms Stratovolcanoes
Most active stratovolcanoes on circum-Pacific mountain belt
Associated with subduction zones
Felsic lavas produce explosive eruptions
Large amounts of gas under high pressure
Central part of volcano may explode, leaving caldera: central depression
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

7. Volcanic Landforms Stratovolcanoes
Exogenic processes erode stratovolcanoes
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

8. Volcanic Landforms Shield Volcanoes
Shield volcanoes are associated with mafic lava (basalt)
Lava thin, not viscous
Holds little gas
Usually quiet eruptions
Lava travels long distances, spreads out in thin layers
Shield volcanoes are rounded domes, with gentle slopes
Shield Volcano: low, often large, dome-like accumulation of basalt lava flows emerging from long , radial fissures on flanks
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

9. Volcanic Landforms Shield Volcanoes
Some shield volcanoes form over hotspots: stationary plumes of basaltic lava welling up from the mantle
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

10. Volcanic Landforms Shield Volcanoes
The Hawaiian chain was formed by the movement of the Pacific Plate over a hotspot.
Chain of islands shows motion of the plate
Active volcanoes at the southern end
Guyots (sunken islands) at the northern end
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

11. Volcanic Landforms Shield Volcanoes Basaltic lava also erupts:
Along midocean ridges
Seafloor spreading
Many volcanic islands along mid-Atlantic Ridge
Beneath continental plates
Hotspot generates large volume of basaltic lava
Forms flood basalts
Basaltic lava on Heimaey Island, Iceland, on mid-Atlantic Ridge
Continental flood basalts, Columbia Plateau, U.S.
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

12. Geothermal Energy Sources
Volcanic Landforms
Geothermal Energy Sources
Geothermal energy is energy from the heat in the Earth
Regions near hot springs and geysers have hot water that can be tapped and used to drive turbines to generate electricity.
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

13. Compression from tectonic activity produces folds in rock strata
Tectonic Landforms
Fold Belts
Compression from tectonic activity produces folds in rock strata
Anticlines: upbends
Synclines: troughs
Folds: corrugations of strata caused by crustal compression
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

14. Fold Belts Folds erode to form ridge-and-valley landscape
Tectonic Landforms
Fold Belts Folds erode to form ridge-and-valley landscape
Ridges and valleys parallel
Folds may be plunging folds
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

15. Faults and Fault Landforms
Tectonic Landforms
Faults and Fault Landforms
Fault: sharp break in rock with a slippage of the crustal block on one side with respect to the block on the other
Fault lines may extend for many kilometers
Most major faults extend down several kilometers
Fault slippage varies from 1 cm to 15 m
Four main types of faults:
Normal
Transcurrent
Reverse
Overthrust
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

16. Faults and Fault Landforms
Tectonic Landforms
Faults and Fault Landforms
Normal faults are produced by crustal extension
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

17. Faults and Fault Landforms
Tectonic Landforms
Faults and Fault Landforms
The East African Rift Valley is a graben
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

18. Tectonic Landforms
Faults and Fault Landforms Transcurrent or Strike-slip Faults are produced when tectonic plates move past each other horizontally
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

19. Faults and Fault Landforms
Tectonic Landforms
Faults and Fault Landforms
Reverse and overthrust faults are produced by compression in the crust
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

20. Faults and Fault Landforms
Tectonic Landforms
Faults and Fault Landforms
Repeated faulting can produce high fault scarps
Landforms are modified by erosion
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

21. Earthquakes
Earthquake: a trembling or shaking of the ground produced by passing seismic waves
Most earthquakes produced by sudden slippage along faults
Energy builds up until the fault slips, releasing seismic waves
Earthquake magnitudes may be described on the Richter Scale
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

22. Earthquakes usually occur on plate boundaries
Large-magnitude earthquakes are generated along subduction zones
Transcurrent faults on transform boundaries cause moderate to strong earthquakes
Spreading plate boundaries produce moderate earthquakes
Some earthquakes occur in the centers of continents, away from plate boundaries
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

23. Earthquakes Along the San Andreas Fault San Francisco Earthquake, 1906
700 lives lost
$30 billion damage
Generated by movement on San Andreas Fault
This portion of the San Andreas has not moved since 1906
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

24. Earthquakes Along the San Andreas Fault
Loma Prieta Quake, 1989
62 lives lost
$6 billion damage
Occurred on fault near the San Andreas
Did not fully relieve strain on San Andreas
Southern California: likelihood of very large earthquake within 30 years is 50%
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

25. Earthquakes
Seismic Sea Waves Tsunami: train of sea waves triggered by an earthquake (or other seafloor disturbance) traveling over the ocean surface
Banda Aceh, Indonesia, before and after 2004 tsunami
Kalutara Beach, Sri Lanka, before and during 2004 tsunami
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.

26. Landforms and Rock Structure
Exposed Batholiths and Monadnocks
Batholiths: huge bodies of intrusive igneous rock
Form hilly or mountainous uplands
Monadnock: a mountain that rises out of a surrounding plain and that develops because it consists of more resistant rock than the bedrock of the surrounding region
Visualizing Physical Geography Copyright © 2008 John Wiley and Sons Publishers Inc.