Geohydrology and Earth's Structure

Geohydrology/Hydrogeology

• Focuses on groundwater movement throughout the environment.

Structure of the Earth

• Earth is composed of various spherical layers categorized by chemical composition and mechanical properties.

Compositional (Chemical) Layers of Earth

• Layers defined by their chemical elements.

Crust

• Composed of various elements, thickness varies: 3-5 miles under oceans, ~25 miles under continents.
• Types of Crust:
  • Oceanic Crust (Basaltic):
    • Makes up 71% of the crust, consists of basalt and gabbro from volcanic activity.
    • Heaviest sedimentation near shores.
  • Continental Crust (Granitic):
    • Accounts for 29%, features a variety of rocks primarily granite, which is less dense than oceanic crust and generally thicker.

Mantle

• Comprises 82% of Earth’s volume, approximately 1,800 miles deep.
• Dominated by magnesium and iron-rich silicate rocks, with convection currents driven by heat.

Core

• Center made primarily of 85% iron and 15% nickel.
• Inner Core:
  • Solid, around 760 miles in radius, temperatures can reach up to 7,000°C.

Geological Features

• Great Rift Valley: Formed by the drifting apart of the Arabian, Indian, and African plates.
• Aleutian Islands: Arc formed due to the subduction of the North American plate under the Pacific plate.
• Ryukyu Islands: Formed by fluctuations in the Earth’s crust.

Weathering Processes

• Erosion: Removal of surface material.
• Transportation: Movement of sediments.
• Deposition: Accumulation of sediments which can form features like sand dunes.
• Weathering can be chemical, physical, or exfoliation.

Engineering Implications of Weathering

• Selecting quarries for construction materials requires assessing the impact of weathering on rock strength.
• Sites near moving dunes are challenging due to potential damage; special measures must be employed if selected.

Types of Geological Formations

• Earthquakes are caused by faults, such as the Sierra Nevada fault which triggered a significant earthquake in 1872.

Magma Characteristics

• Chemical composition affects magma type:
  • Basaltic: Low silica, high temperature.
  • Andesitic: Intermediate silica and properties.
  • Rhyolitic: High silica content with low gas levels.

Classification of Igneous Rocks

• Based on silica content and solidification process.
• Acidic Rocks: High silica (over 66%), light in color.
• Basic Rocks: Low silica (under 50%), darker and denser in color.
• Volcanic rocks: Form from lava cooling on the surface.
• Plutonic rocks: Form beneath Earth's surface, coarse-grained due to slow cooling.

Texture of Igneous Rocks

• Determined by size, shape, and arrangement of minerals.
• Equigranular Texture: Minerals are roughly the same size, commonly found in granites.

Metamorphism Processes

• Metamorphic rocks are formed under high heat, pressure, and mineral-rich fluids without melting.
• Key processes:
  • Recrystallization: Change in mineral size and shape.
  • Phase Change: New minerals formed with the same chemical formula but different structures.
  • Neocrystallization: Formation of new minerals as original minerals become unstable.
  • Pressure Solution: Partial dissolution of mineral grains requiring water.
  • Plastic Deformation: Softening and deformation of minerals under pressure.

Explore the intricate movements of groundwater and the layered composition of Earth in this quiz. Delve into the characteristics of the crust, mantle, and core, and understand the differences between oceanic and continental crusts. Test your knowledge of geohydrology and the Earth's chemical layers.