Re: what is a fault-block mountain

Hi Travis,

Let's first look at what a fault is. A fault results when the earth's crust 
suddenly yields under unequal stress. The crust gets displaced along the 
plane of breakage, also called the fault plane.  This displacement can be 
vertical or horizontal, or a combination of both.  Faults are often of 
great extent along the earth's surface (several kilometers), and they show 
up quite clearly (for example, the San Andreas Fault).  Over time, even 
small faulting movements can add up considerably so that some faults have 
displacements of thousands of meters. 

If you get a situation where a block of crust gets elevated between two 
normal faults, you get what is called a Horst. Horsts make blocklike 
plateaus that have flat tops and steep straight sides. In regions where 
faulting takes place on a grand scale, this produces mountain masses called 
fault block mountains. 

An example of a fault block mountain is the Basin and Range of Nevada. It 
consists of a system of ranges which formed during the Tertiary as a 
consequence of the stretching of the continental crust. The Sierra Nevada 
mountains are a gigantic tilted normal fault-block structure where the 
crust was being extended or pulled apart, and Horsts and Grabens (the 
opposite of a Horst - a block has sunk between two faults) formed with the 
uplifted Horsts becoming the mountain ranges. These mountains are separated 
from the intervening valley floors by normal faults of great displacement. 


Here are some web links on the issue:

The "Geology on the Web"-Site has a geological dictionary: http://www
.geotech.org/survey/geotech/dictiona.html#sectF

This high school website has a good section of faults and faulting: http://www.blackgold.ab.ca/science/science_8_pages/unit_4/8scu4t4l1.ht
ml

There is a good graphic here at Volcano World that illustrates how a 
fault-block is uplifted: http://volcano.und.nodak.edu/vwdocs/vwlessons/lessons/Ch1CMA/Answer
_Key_Rev
iew_1.html

The Department of Geosciences at Penn State talks about types of Mountain 
Belts: http://www.ge
osc.psu.edu/~engelder/geosc20/lect30.html

And last but not least, this is a good introductory textbook, if you want 
to know more about Physical Geography and Geology:
Strahler, A. N., Strahler, A. H., 1989: Elements of Physical Geography. 4th 
Edition.


****************
Katja Bach, B.Sc. (Geography), Ph.D. (Remote Sensing)

RADARSAT International  
Richmond, British Columbia, Canada
kbach@rsi.ca   www.rsi.ca         
*****************