E

geo

I. Stress & Strain

Key Vocabulary:

  • Stress – The force applied to a rock.

  • Strain – The rock's response to stress (change in shape or volume).

  • Compression – Squeezing stress.

  • Tension – Pulling apart stress.

  • Shear – Stress that causes rocks to slide past each other.

Types of Deformation:

  • Elastic – Temporary deformation; rock returns to original shape.

  • Ductile – Permanent bending or flowing.

  • Brittle – Permanent breaking or fracturing.

What determines if a rock will deform ductile or brittle?

  • Temperature – Higher temps = more ductile.

  • Pressure – Higher pressure = more ductile.

  • Rate of Stress – Slow = ductile; Fast = brittle.

II. Folds

Definition: Bends in rock layers caused by compressional stress and ductile deformation.

Types of Folds:

  • Anticline – Upward arching fold.

  • Syncline – Downward trough-like fold.

  • Tight Fold – Fold with a small angle between limbs.

  • Overturned Fold – One limb is tilted beyond vertical.

  • Recumbent Fold – Fold is lying on its side; horizontal orientation.

III. Faults

Definition: Breaks in rock where movement has occurred, caused by brittle deformation.

Anatomy of a Fault:

  • Hanging Wall – Rock above the fault plane.

  • Footwall – Rock below the fault plane.

Types of Faults:

  • Strike-Slip Fault – Horizontal movement (caused by shear stress); found at transform boundaries.

  • Reverse Fault – Hanging wall moves up (caused by compression); found at convergent boundaries.

  • Normal Fault – Hanging wall moves down (caused by tension); found at divergent boundaries.

Special Features:

  • Horst – Block of rock uplifted between normal faults.

  • Rift Valley – Block of rock that sinks between normal faults.

IV. Mountain Building (Orogeny)

Definition: Formation of mountains through tectonic processes.

By Plate Boundary Type:

  • Convergent: Oceanic-Continental

    • Forms volcanic mountains.

    • Ex: Andes Mountains

  • Convergent: Oceanic-Oceanic

    • Forms volcanic island arcs.

    • Ex: Japan, Aleutian Islands

  • Convergent: Continental-Continental

    • Forms non-volcanic mountains.

    • Ex: Himalayas

  • Divergent

    • Forms fault-block mountains.

    • Ex: Basin and Range Province, Western U.S.

Isostasy:

  • The balance between Earth's crust and mantle.

  • The crust “floats” on the denser mantle like an iceberg in water.