13.2 Tectonic geomorphology and active faulting

Tectonic geomorphology explores how Earth's surface changes due to tectonic forces and erosion. It's crucial for understanding landscape evolution, revealing how mountains form, rivers change course, and landforms develop over time.

Active faulting plays a key role in shaping topography. Fault scarps, offset streams, and unique drainage patterns are telltale signs of tectonic activity. These features help geologists piece together Earth's dynamic history and predict future changes.

Tectonic Geomorphology: Landscape Evolution

Defining Tectonic Geomorphology

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• Tectonic geomorphology studies interaction between tectonic and surface processes shaping Earth's landscape over time
• Integrates concepts from structural geology, geophysics, and geomorphology to understand tectonic influence on landform development
• Provides insights into rates and patterns of crustal deformation, crucial for assessing seismic hazards and long-term landscape evolution
• Allows reconstruction of past tectonic events and prediction of future landscape changes by analyzing geomorphic features and their relationships
• Essential for understanding dynamic nature of Earth's surface and its response to endogenic and exogenic processes
• Employs various techniques to quantify landscape evolution
  • Remote sensing
  • Field observations
  • Geochronology
  • Numerical modeling

Significance in Landscape Evolution

• Reveals interaction between internal and external Earth processes
• Helps identify areas of active tectonism and potential seismic hazards
• Enables reconstruction of past tectonic events (uplift history of mountain ranges)
• Aids in understanding long-term landscape development and erosion patterns
• Provides insights into sediment transport and deposition in tectonically active regions
• Supports natural resource exploration by revealing structural controls on mineral deposits
• Informs land-use planning and infrastructure development in tectonically active areas

Active Faulting Indicators

Topographic Features

• Fault scarps form steep, linear breaks in topography from vertical displacement along fault plane
  • Indicate recent or ongoing tectonic activity
  • Height and morphology can reveal fault slip history
• Triangular facets develop as triangular-shaped hillslopes at mountain front bases due to normal faulting and erosion
  • Size and steepness relate to fault activity and erosion rates
• Shutter ridges create elongated hills from lateral movement of strike-slip faults
  • Can block or deflect drainage patterns (Carrizo Plain, California)
• Pressure ridges and sag ponds form along strike-slip faults due to local geometry variations
  • Pressure ridges: compressional features (uplifted areas)
  • Sag ponds: extensional features (depressions often filled with water)

Drainage System Indicators

• Offset streams exhibit abrupt changes in course or channel morphology crossing active fault lines
  • Often show lateral displacement (Wallace Creek, San Andreas Fault)
• Tectonic uplift creates knickpoints in river profiles
  • Abrupt changes in channel gradient propagate upstream over time
• Linear valleys and aligned drainage patterns indicate active faults
  • Erosion exploits zones of structural weakness
• Wind gaps and water gaps develop where rivers cut through uplifting terrain
  • Wind gaps: abandoned river courses
  • Water gaps: active river courses through uplifted areas

Active Faulting: Shaping Topography

Regional Landform Development

• Active faulting creates and maintains relief in landscapes
  • Offsets rock units
  • Creates zones of weakness for preferential erosion
• Fault systems control development of major landforms
  • Mountain ranges (Sierra Nevada)
  • Basins (Basin and Range Province)
  • Valleys (Rift valleys like East African Rift)
• Interaction between fault-driven uplift and erosional processes determines mountainous terrain morphology
• Fault activity leads to sedimentary basin formation through subsidence
  • Affects sedimentation patterns and landscape evolution (San Joaquin Valley, California)

Drainage Network Influence

• Active faulting influences drainage patterns and river network development
  • Creates topographic barriers
  • Changes base levels
  • Alters channel gradients
• Faults can cause river capture or diversion (Gunnison River capture, Colorado)
• Creates localized zones of high erosion rates
  • Leads to development of unique geomorphic features (wind gaps, water gaps)
• Influences sediment transport and deposition patterns in fault-bounded basins
• Can cause drainage reversals or formation of endorheic basins in tectonically active regions

Fault Type, Slip Rate, and Landforms

Fault Types and Associated Landforms

• Normal faults create asymmetric mountain ranges with steep fault scarps and tilted fault blocks
  • Example: Wasatch Range, Utah
• Reverse faults produce more symmetrical mountain ranges with thrust-related folding
  • Example: San Gabriel Mountains, California
• Strike-slip faults generate characteristic features
  • Offset drainages
  • Shutter ridges
  • Pull-apart basins (Dead Sea Basin)
  • Degree of offset related to fault's slip rate and age

Slip Rate and Landscape Evolution

• Slip rates on active faults control rate of landscape change
  • Higher slip rates generally produce more pronounced and rapidly evolving geomorphic features
• Interplay between fault slip rate and erosion rate determines dominant landscape evolution process
  • Tectonic uplift vs. surface erosion
• Variations in slip rate along a fault lead to differential uplift or subsidence
  • Creates complex topographic patterns
  • Influences drainage network development
• Persistence and preservation of fault-related landforms depend on balance between tectonic activity and surface processes
  • Slip rate vs. erosion and deposition rates
• Fault slip rates can be estimated using offset geomorphic markers and dating techniques
  • Allows quantification of long-term landscape evolution rates