Springs and Their Classification | Geology Optional Notes for UPSC PDF Download

11.7 Springs and Their Classification

• Definition of Springs

  Springs are natural formations where water from deeper subsurface flows on the earth's surface, creating visible flow. The flow is influenced by the position of hydraulic head in a confined aquifer and the elevation of the land surface.

• Formation of Springs

  For a spring to form, the water head must be above the land surface. Springs can also form above the unconfined aquifer if the water table intersects the ground. It is important to note that water supplied by capillary action is not classified as a spring.

• Types of Springs

  • Artisan Springs

    Artisan springs are formed due to pressure within a confined aquifer and are also known as arising or ascending springs. The water in these springs can be deep-seated or shallow, with shallow water mainly contributed by precipitation and deep-seated water having a more complex origin, possibly magmatic or sedimentogenic.

• Classifications of Springs

  • Based on Temperature

    Springs are classified into warm springs and hot springs based on their water temperature. Warm springs have an average temperature of 37°C in cold climates, while hot springs have temperatures higher than the ambient atmospheric temperature. Boiling springs have water temperatures close to boiling point and are also known as thermal springs.

    • Cool Springs

      Cool springs have very cold water temperatures and may be influenced by factors like a sandy bottom or the presence of gas or vapor emissions.

    • Geysers

      Geysers are hot springs that emit steam and hot water, often associated with well-defined openings under pressure. Famous locations of geysers include New Zealand, Yellowstone Park, and Iceland.

Hydrology

Classification of Springs

• Classification Based on Flow

  • Perennial Springs: Flow throughout the year.
  • Intermittent Springs: Active during specific seasons.
  • Periodic Springs: Flow for a specific period.
  • Ebbing and Flowing Springs: Occur along seashores due to density differences.

• Classification Based on Geomorphologic Control

  • Mound and Knoll Springs: Found on mounds in arid climates.
  • Pool Springs: Large basin-like structures with water filling.

• Classification Based on Source of Water

  • Volcanic Springs: Associated with volcanic activities.
  • Fissure Springs: Formed along tectonic lines with fractures.

Spring types can be classified based on flow patterns, geomorphological features, and water sources. Perennial springs flow consistently, intermittent springs are active seasonally, periodic springs flow for a specific time, and ebbing and flowing springs vary with tides. Geomorphologic classifications include mound and knoll springs on wind-built mounds and pool springs with basin-like structures. Springs can also be categorized based on their water sources, such as volcanic springs linked to volcanic activity and fissure springs along tectonic lines.

Shallow Water Spring

• Definition and Classification

  Shallow water springs are supported by meteoritic water sustained by the hydrostatic head of an aquifer, originating at a relatively shallow depth. They can be classified into four classes:

  • Spring in Porous Rocks

    These springs form when the water table reaches or is above the ground level. Gravity plays a significant role in their flow. Examples include dimple springs, valley springs, channel springs, and border springs.

  • Spring in Porous Rock Overlying Impervious Rocks

    When porous rock overlies an impervious bed, water migrates to the surface due to gravity. These are known as contact springs and can be categorized based on the attitude and surface at the contact into horizontal, incline, and irregular types.

  • Spring in Porous Rock Between Impervious Rocks

    This type of spring occurs in porous rock sandwiched between impervious rocks. The movement of water to the surface is influenced by the geological structure.

  • Spring in Impervious Rock

    These springs are found in impervious rock formations where water is brought to the surface due to changes in the slope of the land surface.

• Examples and Explanations

  For instance, dimple springs form in depressions on hills where the water table intersects with the surface. Valley springs emerge due to abrupt slope changes between flood plains and valleys. Channel springs develop in depressions caused by channel deepening processes. Border springs arise from gradients in flat alluvial slopes.

• Hydrology
  • Horizontal Impervious Media: Found in horizontal springs, with three subclasses:
    • Gravity Springs: Porous material over an impervious bed, forming a mound where water moves by gravity along the contact line.
    • Hardpan Springs: These have a small underlying impervious bed that forces water to rise by gravity in the porous media above. They are common in perched aquifers above the normal water table.
    • Mesa Springs: In this type, the overlying material is hard but porous, containing water that percolates down and moves along the contact line between formations.
  • Incline Category: Impervious bed with an inclined angle, where water in the porous media is above this surface. Water migrates along the incline surface due to gravity and seeps at the contact point of both media at the lower side. Springs in this category may be termed gravity spring, cuesta spring, or hardpan springs.
  • Spring in Porous Rock Between Impervious Rocks: Sustained by porous media between two impervious rocks.

Horizontal springs have subclasses that include gravity springs, hardpan springs, and mesa springs. Gravity springs feature porous material over an impervious bed, allowing water to move by gravity. Hardpan springs have a small underlying impervious bed that forces water to rise by gravity in the porous media above. Mesa springs involve hard, porous overlying material containing water that percolates down.

In the incline category, water in the porous media is above the inclined surface, migrating along the incline due to gravity and seeping at the contact point. Springs in this category may be termed gravity spring, cuesta spring, or hardpan springs. Additionally, springs sustained by porous media between impervious rocks are also observed.

Understanding Aquifer Springs

• Artesian Springs

  • Artesian Dip Spring

    These springs occur when a pervious bed dips in a way that the upper part receives water to sustain the spring in the lower end. They are commonly found in sedimentary layered rocks and intertrappean beds in lava formations.

  • Siphon Artesian Spring

    In folded structures, siphon artesian springs are located. The porous media acts as an inverted siphon, recharging from the flanks and resulting in springs on the lower side of the structure.

  • Unbedded Artesian Spring

    These springs are found in formations with irregular bedding. The porous medium receives recharge at the top end, sustaining a spring on the lower side of the unconsolidated deposits.

  • Fracture Artesian Springs

    In fracture artesian springs, porous media lies between impervious layers, allowing water flow through fractures in the overlying impervious rocks due to hydraulic pressure.

• Spring in Impervious Rocks

  • Tubular Springs

    Vertical springs where water moves vertically. This type is further divided into three categories based on their characteristics.

  • Fracture Springs

    These springs occur in rocks with secondary permeability or capillary-sized pore spaces, allowing water flow through vertical or horizontal openings.

Hydrology Concepts

• Solution Springs

  Solution springs are found in regions where aquifers are enlarged due to the dissolution of rocks by circulating water. These springs require specific formations to exist.

  Good formations for sustaining solution springs include limestone, calcareous rocks, sandstone, and salts.

  For example, limestone formations are known to sustain solution springs due to their chemical composition.

• Lave Tubular Springs

  Lave tubular springs are situated in volcanic formations where caverns and tunnels are created through igneous intrusion processes.

  Tube-like features are formed from the rapid cooling of lava at the surface, which facilitates the flow of water.

  One example is the formation of tube-like structures in volcanic regions such as Hawaii, where lava tubes sustain the flow of water.

• Fracture Springs

  Fracture springs emerge from sheet-like or plate-like geological features such as joints, bedding plains, faults, and columnar joints.

  The water intensity in fracture springs is influenced by the quantity of fractures present in the rock formations.

  For instance, areas with extensive fractures like columnar joints have a high potential for fractured rock springs.