Section 13: Weathering, Karst Landscapes, and Mass Movement

SLOs: denudation and geomorphology, weathering, mass movement.


Lesson 1:

Instruction

Denudation is defined as the processes of wind and water that dissolve, dislodge, or remove surface crustal materials.  Weathering and mass movement, characterized by erosion, transportation, and deposition, are the processes of wind and water that allow for denudation.  Geomorphology, or landforms science, is predominantly the study of these features.  Most geomorphologists support the dynamic equilibrium model, emphasizing a balance between uplift and reduction processes.  As land masses are uplifted over time, so are they reduced through weathering and mass movement.  One of the best examples of uplift and reduction can be shown using any slope (an inclined surface acting as a landform boundary) on a hillside.  The theoretical hill top we are discussing has been formed by uplift over a long period of time, which is why the hill top is higher in elevation than, say, the valley below.  However, because there is a slope in between the hill top and the valley, weathering and mass movement (accompanied by the effects of heat, chemical, and kinetic energy) reduce the size of the hill top over time.  When a landform is at sea level, that landform is said to be at equilibrium in terms of energy and relief.  However, when a landform such as our theoretical hill top is far above sea level, this landform is at disequilibrium and is vulnerable to reduction processes exacerbated by the force of gravity.                   

Photos and Images
 (slope properties)  

Quiz

The California coast line, including the coast along Ventura County, is an erosional coastline.  Name three places within Ventura County where you can find erosion along the coast.  

 


Lesson 2:

Instruction

Weathering processes have the power to disintegrate and dissolve bedrock into sediments.  Physical weathering (change in size and shape) and chemical weathering (change in rock minerals) are two different types of weathering.  Both types of weathering are influenced by the kind of bedrock that is being reduced, the climate of the area near the bedrock, the orientation of slopage on a hillside, and the presence or absence of vegetation.  In Ventura County, there are many instances of weathering.     

Photos and Images

 
 (beach sand formed from erosion of the bedrock inland, Mandalay State Beach) (sediments eroded from a hillside, Los Padres National Forest) (rocks eroded away from bedrock above, Santa Susana Pass)

Quiz

Using Google Earth, find the Los Padres National Forest (in the northern section of the county).  Zoom in to find a topographic example of weathering on a hillside anywhere within the forest.  Describe the characteristics of this hillside and give a latitude/longitude for the location of this erosion example.

 


Lesson 3:

Instruction

Mass movement refers to any movement consisting of a large body of material.  This includes multiple types of slides, falls, and flows, avalanches, karst landscapes, soil creeps, sinkholes, and human induced disturbances that can result in all of the above mentioned types of movement.  In Ventura County, only a few of these mass movement classes are abundant (like slides and falls), including the human induced disturbances.          

Photos and Images
    (land slide after a rain on burnt soils from the Box Canyon fire)    (debris avalanche at La Conchita caused by El Nino conditions)  (mud slides at Rincon Parkway from agricultural runoff atop the hill)     (rock slide in the Santa Monica National Recreation Area caused by natural erosion)    

Quiz

Which of the mass movement examples shown above were influenced by human activities?  Why?      


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2006 Jessica Douglas