MITIHANI POPOTE EXAMINATION SERIES KARST REGIONS & UNDERGROUND WATER (With answers)

KARST REGIONS & UNDERGROUND WATER

1. Explain the surface and subsurface features found in Karst/Limestone region

   Karst landscapes develop on soluble rocks (primarily limestone) and display distinctive surface and subsurface features:

   Surface Features:

   • Lapies/Karren: Small grooves and ridges on exposed limestone surfaces
   • Dolines: Circular depressions (10-100m diameter) formed by dissolution
   • Uvalas: Larger depressions formed by merging dolines
   • Poljes: Large flat-floored depressions (km-scale) with steep sides
   • Dry valleys: Former river valleys left dry as drainage went underground
   • Limestone pavements: Flat exposures of limestone with clints (blocks) and grikes (gaps)
   • Disappearing streams: Surface streams that vanish into swallow holes

   Subsurface Features:

   • Caves/Caverns: Underground chambers formed by dissolution
   • Stalactites: Icicle-shaped deposits hanging from cave ceilings
   • Stalagmites: Upward-growing deposits from cave floors
   • Pillars/Columns: When stalactites and stalagmites join
   • Flowstones: Sheet-like deposits formed by flowing water
   • Sinkholes: Collapse features when cave roofs give way
   • Underground rivers: Subterranean drainage systems

   [Diagram showing cross-section of karst landscape with surface and subsurface features]

   Formation process: Carbonation (CO₂ + H₂O + CaCO₃ → Ca(HCO₃)₂) dissolves limestone along joints and bedding planes, gradually enlarging openings.

2. Discuss the features of water action in Karst regions

   Water action in karst regions creates unique hydrological and geomorphological features:

   Surface Water Features:

   • Intermittent streams: Flow only during wet periods
   • Swallow holes (ponors): Points where surface water enters underground
   • Resurgences: Where underground water reappears at surface
   • Estavelles: Features that alternate between swallow holes and springs

   Underground Water Action:

   • Solution channels: Networks of enlarged joints forming underground drainage
   • Phreatic zones: Where all cavities are water-filled
   • Vadose zones: Where water percolates downward through air-filled cavities
   • Underground waterfalls: Where water drops between cave levels

   Chemical Deposition Features:

   • Speleothems: Various cave formations created by calcite deposition
   • Rimstone dams: Calcite barriers forming pools in caves
   • Helictites: Twisted stalactites defying gravity

   [Diagram showing karst hydrology with recharge, flow, and discharge areas]

   Unique characteristics: Karst systems often have rapid water transmission (hours-days) compared to porous aquifers (years), making them vulnerable to contamination.

3. Explain how underground water can be polluted and measures to avoid pollution

   Sources of Groundwater Pollution:

   Pollution Source	Contaminants	Impact
   Agricultural runoff	Nitrates, pesticides, herbicides	Eutrophication, health risks
   Industrial waste	Heavy metals, solvents, chemicals	Toxicity, carcinogenic effects
   Landfills	Leachate with organic compounds	Oxygen depletion, toxicity
   Septic systems	Bacteria, viruses, nutrients	Waterborne diseases
   Road salts	Chlorides	Salinization, corrosion
   Mining activities	Acid mine drainage, metals	Acidification, toxicity

   Prevention and Protection Measures:

   • Land-use zoning: Restrict polluting activities near recharge areas
   • Proper waste disposal: Engineered landfills with liners
   • Agricultural best practices:
     • Controlled fertilizer application
     • Buffer zones along watercourses
     • Integrated pest management
   • Monitoring wells: Early detection of contaminants
   • Artificial recharge: Using clean surface water to replenish aquifers
   • Public education: Proper chemical disposal and water conservation

   Remediation techniques: Pump-and-treat, bioremediation, air sparging, permeable reactive barriers

4. Explain the origins/types of underground water (classify underground water)

   Groundwater can be classified based on origin and geological occurrence:

   By Origin:

   • Meteoric water: Derived from precipitation infiltrating through soil
   • Connate water: Trapped in sedimentary rocks during deposition
   • Juvenile water: Magmatic origin from volcanic activity
   • Comate water: Ancient water isolated from hydrologic cycle

   By Geological Occurrence:

   Type	Description	Examples
   Unconfined aquifer	Water table aquifer with permeable layer above	Alluvial aquifers
   Confined aquifer	Bounded above and below by impermeable layers	Artesian aquifers
   Perched aquifer	Localized water table above main aquifer	Lens-shaped deposits
   Fractured aquifer	Water in rock fractures rather than pores	Basalt, granite aquifers
   Karst aquifer	Solution channels in carbonate rocks	Limestone regions

   [Diagram showing different aquifer types in cross-section]

   Water table variations: Depth fluctuates seasonally and with pumping, typically following surface topography but more subdued.

5. Explain the geological structures of springs formation (types of springs)

   Springs form where groundwater emerges at the surface, with different types based on geological controls:

   Spring Type	Formation Mechanism	Characteristics
   Contact spring	Permeable rock overlies impermeable layer	Emerges at contact boundary
   Fracture spring	Water follows rock fractures to surface	Often localized point source
   Fault spring	Fault plane brings aquifer to surface	May be linear along fault trace
   Karst spring	Emerges from limestone solution channels	Often large discharge (Vauclusian springs)
   Artesian spring	Pressurized aquifer intersects surface	Flows without pumping
   Depression spring	Water table intersects ground surface	Common in valleys
   Thermal spring	Heated water from deep circulation	Warmer than local groundwater

   [Diagram showing cross-section with different spring types]

   Spring discharge characteristics: Varies from constant (from deep aquifers) to highly variable (shallow systems). Mineral springs contain dissolved solids (>1000 mg/L).

6. Explain the conditions for the formation of Artesian wells and uses of artesian wells

   Conditions for Artesian Wells:

   1. Confined aquifer: Water-bearing layer between impermeable strata
   2. Recharge area: Higher elevation where aquifer is exposed
   3. Hydraulic gradient: Recharge area higher than well location
   4. Adequate permeability: Allows water to flow through aquifer
   5. Structural trap: Syncline or monocline to maintain pressure

   [Diagram showing artesian system with recharge area, confined aquifer, and flowing well]

   Types of Artesian Wells:

   • Flowing artesian: Water rises above ground surface naturally
   • Non-flowing artesian: Water rises in well but doesn't reach surface

   Uses of Artesian Wells:

   • Municipal water supply: Natural pressure reduces pumping costs
   • Irrigation: Consistent flow for agricultural use
   • Bottled water: Often marketed as "natural spring water"
   • Geothermal energy: When water is naturally heated
   • Historical significance: Early civilizations valued reliable water sources

   Famous examples: Great Artesian Basin (Australia), Dakota Aquifer (USA), London Basin (UK)

   Management challenges: Overuse can reduce pressure permanently, requiring careful monitoring of extraction rates.