Section 12: Tectonics, Earthquakes, and Volcanism

SLOs: topography and orogenesis, volcanism and folding/faulting, earthquakes.


Lesson 1:

Instruction

Topography is defined as Earth's surface form.  Topography includes multiple orders of relief, or the changes in elevation of Earth's surface.  Mountain building processes, termed orogenesis, are part of the what makes the topography of Earth so diverse.  The process of mountain building is very complex and occurs over long periods of time in different stages.  The three types of orogenesis through plate movements are: oceanic-continental plate collision, oceanic-oceanic plate collision, and continental-continental plate collision.  The Transverse Ranges in Ventura County (within the Los Padres National Forest and Santa Monica National Recreation Area, for example) were created through uplift of the Pacific plate as it rubbed against the North American plate at the San Andreas Fault.  Smaller faults also run through Ventura County and cause uplift, especially throughout the mountain chain addressed above.               

Photos and Images
 (uplift in the Los Padres National Forest)     (more uplift in the Los Padres National Forest)

Quiz

The outcomes of orogenesis in our region are very prominent.  Name three specific mountains in Ventura County that have been formed by uplift.  Use Google Earth to locate the exact names, locations, and elevations of these mountains.

 


Lesson 2:

Instruction

Multiple types of crustal formation processes exist worldwide.  In the last section we discussed sea-floor spreading.  The crust that is made during this process shifts over time away from its source as either oceanic or continental crust.  However, volcanic activity also adds material to the Earth's crust as both oceanic and continental crust.  Terrain that is uplifted near subduction zones or hotspots (holes) in Earth's crust can form perfect conditions for the formation of active volcanoes.  Multiple types of crustal deformation processes also exist globally.  All rocks can be subjected to tectonic forces, gravity, and pressure from other rocks.  This stress causes tension, in which rocks are stretched, compressed, or sheared, torn, and twisted.  When rocks are strained (stressed) the physical appearance of these rocks change.  Some rocks are faulted (broken) or folded (bended).  Those that are faulted, are literally broken in two or more pieces.  These faults are considered in three categories: normal (tension stress pulling the rocks apart), reverse or thrust (compression that forces the rocks upward), and strike-slip (horizontal movement created by lateral shearing).  Those rocks that are folded come out in two main forms: anticlines and synclines.  Anticlines are dome-shaped rock arrangements, while synclines are bowl-shaped rock arrangements.           

Photos and Images

 
 (fault in the Transverse Range, Los Padres National Forest) (fold in the Transverse Range, Los Padres National Forest)

Quiz

Locate the fault in the first photograph and name the type of folding in the second photograph, above.  What causes the stress on these rocks?

 


Lesson 3:

Instruction

The majority of all earthquakes in the United States are located in or around California, as well as within the state of Alaska.  Earthquakes are the product of great friction between plate boundaries or smaller faults.  This friction is released when Earth's subterranean crust along a fault line breaks (the focus) and/or moves rapidly.  Earth's crust is a solid mass, so earthquakes can influence topography far from their epicenter, or origin.  Movements along the fault line may precede (as a foreshock) or follow (as an aftershock) before or after the main earthquake, respectively.  Earthquakes are measured by seismographs (instruments recording crustal vibrations) and categorized using the Richter scale (a logarithmic relation of magnitude and released energy).  The San Andreas fault located east of Ventura County is the most influential plate boundary and fault line within all of California.  Many earthquakes have been felt in our area because of its activity.  Since this plate boundary is so active, it is important for people living nearby to be prepared for an earthquake.                   

Photos and Images
    (transform plate boundary)      

Quiz

Your assignment is to prepare your household for an earthquake.  Store enough food and water to last for a week, buy or find your first aid kit, and make plans with your family/roommates for such an emergency.  If a serious earthquake hits our area, it is also useful to know what to do.  If you find yourself in a building during an earthquake, stay away from windows/glass and any heavy objects that may fall over.  Standing under doorways or desks is no longer the preferred option.  Earthquake rescue specialists now suggest curling up into a fetal position next to large furniture, such a couch or bed (this area is called "the triangle of life").  Also, attempt to get outside or closest to the outer walls in a structure, if possible.  This allows for a better chance of rescue.  The U.S.G.S. has a website for documentation of earthquake effects.  If you ever experience earth movements, you can go onto this site (at http://quake.usgs.gov/) to get information about the event, plus add comments on the characteristics of the quake that are very useful to seismologist.   


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2006 Jessica Douglas