Arguing Causes of Faults & Folds—Sponge Fault Model

The faults and folds in rocks provide evidence that the rocks are subjected to compressional, tensional, and/or shear stress.

Students begin this activity by experimenting with Silly Putty™  to identify different stresses that rocks can experience, and examining the relationship between stress type and strain. This lays the foundation for students to understand that the structure (strain) we see in rocks provides evidence for they type of stress that caused it. Students apply this idea by examining images of faults and folds to determine how the structures formed. Additional evidence is collected through experimentation with sponge models. Students summarize their ideas and evidence for each image in a short written paragraph or in alternative presentation format. Sponge models are particularly useful because they allow students to interact physically with the models to consider the forces necessary to create these features as well as visualizing deformation in 3-D. Sponge models can be constructed using inexpensive materials obtained from a dollar store or any home improvement store.

Objectives:

Students will be able to:

  • Use foam models to demonstrate the forces and relative motions of a block of rock to form of anticlines and synclines.
  • Use foam models to demonstrate the forces and relative motions acting on blocks of rock to form normal, reverse and strike-slip faults.
  • Use evidence to support or refute the claim made in an argument. 


Level: Novice

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In a normal fault, the block above the fault moves down relative to the block below the fault. This fault motion is caused by tensional forces and results in extension. Other names: normal-slip fault, tensional fault or gravity fault. Examples: Sierra Nevada/Owens Valley; Basin & Range faults.

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In a reverse fault, the block above the fault moves up relative to the block below the fault. This fault motion is caused by compressional forces and results in shortening. A reverse fault is called a thrust fault if the dip of the fault plane is small. Other names: thrust fault, reverse-slip fault or compressional fault]. Examples: Rocky Mountains, Himalayas.

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In a strike-slip fault, the movement of blocks along a fault is horizontal. The fault motion of a strike-slip fault is caused by shearing forces. Other names: transcurrent fault, lateral fault, tear fault or wrench fault. Examples: San Andreas Fault, California; Anatolian Fault, Turkey.

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