Lecture on Water and Landforms by Water

Introduction

• Focus on fresh water on the planet.
• Review of previous discussions on water.
• Exploration of landforms created by fresh water and ocean water.
• Importance of water for survival and ecosystems.
• Extra credit opportunity: Watch Planet Earth videos on freshwater and caves.

Importance of Water

• Essential for survival of all living organisms.
• How we use and treat water impacts our survival and the environment.
• Fresh water is only 1% of the Earth's water.

Hydrologic Cycle

• Evaporation: Mostly from oceans, water turns to vapor leaving minerals behind.
• Condensation: Vapor condenses to form clouds, needing condensation nuclei.
• Precipitation: Water rains down, absorbed into the ground (infiltration).
• Groundwater: Water stored in the subsurface, in soil and aquifers.
• Infiltration: Water absorbing into soil and regolith is crucial for the hydrologic cycle.
• Evapotranspiration: Total water vapor from evaporation and transpiration.

Water Distribution

• 70% of the Earth’s surface is water; 97% is saltwater, 2% frozen, 1% accessible freshwater.
• Examples of freshwater: Great Lakes, Amazon River (largest by volume and length).

Groundwater and Aquifers

• Groundwater: Subsurface water stored in soil and aquifers.
• Infiltration: Essential for groundwater replenishment; impacted by human activities (e.g., cement reduces infiltration).
• Water Table: Upper limit of an aquifer where there’s more water than soil.
• Aquifers: Underground rivers, concentration of water held by impermeable rock layers (occludes).
• Cone of Depression: Land sinks due to over-withdrawal of groundwater.
• Hot Springs: Result from geothermal heating of groundwater (e.g., Yellowstone).
• Karst Topography: Formed by erosion of limestone by carbonic acid, leading to caves and underground water storage.

Rivers and Drainage Systems

• Drainage Basin: Area drained by a river system, e.g., Mississippi River Basin.
• Drainage Patterns: Determined by topography, rock type (dendritic, trellis, annular, radial patterns).
• Stream Channels: Formed by water flow from high to low elevation.
• Floodplains: Areas prone to flooding, important for nutrient-rich soil.
• River Meanders: Curves in a river; oxbow lakes form from abandoned meanders.
• Velocities and Gradients: Affect the shape and depth of river channels.
• Age of Rivers: Young (V-shaped), Middle-aged (meanders), Old (wide meanders, oxbow lakes).

Water Issues and Human Impact

• Overdrawing Groundwater: Leads to depletion and land depression.
• Agricultural Practices: Water-intensive crops (e.g., almonds) in dry areas deplete water sources.
• Urban Sprawl: Cement reduces infiltration, increasing run-off into oceans.
• Pollution: Agricultural run-off creates dead zones (e.g., Gulf of Mexico).
• Sustainable Practices: Crop rotation, using permeable materials for urban development.

Global Water Distribution

• North America: Rich in freshwater resources (Mississippi, Great Lakes).
• South America: Amazon River, largest by volume.
• Africa: Significant water sources (Niger, Congo Rivers).
• Australia: Very limited freshwater resources.
• Europe/Asia: Major rivers and aquifers.
• Canada: 60% of the world's lakes due to historical ice sheets.

Conclusion

• Next topic: How water carves out the landscape.