Geological Processes and Uniformitarianism

Geological Processes

• Weathering, erosion, and deposition are simultaneous geological processes that reshape landscapes over time.
• Weathering breaks down large rocks into smaller pieces due to wind, water, and glaciers.
• Erosion moves broken rock fragments from one place to another, agents include wind, water, and glaciers.
• Water erosion is generally faster than wind or glacial erosion.
• Deposition accumulates eroded materials in new areas, shaping landscapes.

Uniformitarianism and Landform Analysis

• Uniformitarianism suggests that past geological processes were similar to present-day processes.
• Four principles aid in determining the order of events in landform diagrams:
  • Law of original horizontality: Layers of rock are initially horizontal.
  • Law of superposition: Younger rock layers lie above older ones.
  • Cross-cutting relations: Features that cut across other layers are younger.
  • Unconformities: Gaps in the rock record represent missing time.

Stream Valleys

• Stream valleys are depressions where streams flow.
• Erosion by flowing water creates and modifies stream valleys.
• Stream valleys progress through youth, maturity, and old age stages.
  • Youth: Steep gradient, V-shaped valley, fast flow, downward erosion.
  • Maturity: Less steep gradient, U-shaped valley, slower flow, outward erosion, floodplain.
  • Old Age: Extremely low gradient, broad, flat valley, wide, slow-moving waterway.

Base Level of Streams

• Base level is the lowest point to which a stream can erode its channel.
• Ultimate base level: Sea level.
• Local (temporary) base level: Lakes, dams, waterfalls.
• At the base level, water velocity affects erosion and deposition rates.

Bedrock Channels

• Bedrock is solid rock, often covered by alluvium (loose soil and sediments).
• Bedrock channels are erosion paths carved through bedrock.
• Stream power is the energy for erosion.
• Abrasion: Sandpaper-like erosion from particles.
• Plucking (quarrying): Large rock chunks removed by glaciers.

Alluvial Channels

• Alluvial channels are constantly changing due to water flow, erosion, and deposition.
• Alluvium: Loose sediments deposited in channels.
• Four channel types:
  • Meandering: Winding streams with loops.
  • Braided: Interwoven channels separated by sediment bars.
  • Straight and sinuous: Linear appearance with sinuous flow.
  • Anastomosing: Interconnected streams.
• Features formed: oxbow lakes, floodplains, natural levees, terraces.

Groundwater

• Most Earth's liquid freshwater is underground.
• Groundwater exists in saturated and unsaturated zones, separated by the water table.
• Aquifers: Underground water reservoirs (limestone).
• Groundwater carries sediment, forming sedimentary rock.
• Groundwater can heat up near surface magma creating geysers.
• Removing groundwater too quickly can cause sinkholes and cave formation.

Groundwater Movement

• Groundwater moves through the earth due to porosity, permeability, and gravity.
• Porosity: Amount of water soil can hold.
• Permeability: Speed of water movement.
• Gravity: Direction and rate of flow.
• Aquifers: Confined (bounded by impermeable layers) and unconfined (exiting valleys).
• Springs: Groundwater exit points (various discharge amounts). Spring water quality depends on proximity to human activity and mineral composition.