A cone of depression forms when:

1. A stream flows into a sinkhole
   
2. Water in the zone of aeration is replaced by water from the zone of saturation
   
3. A spring forms where a perched water table intersects the surface
   
4. Water is withdrawn from a well faster than it can be replaced
   

Choose the correct answer from the options given below:

Correct option is B

Introduction:

• A cone of depression occurs when water is removed from an underground aquifer by a well at a faster rate than it can be replenished by the surrounding groundwater.
• This results in a lowering of the water table around the well, forming a depression that resembles the shape of a cone.
• This phenomenon is particularly common in areas where groundwater extraction exceeds the natural recharge rate of the aquifer.

Information Booster:

• Aquifers are underground layers of rock or sediment that store water. The upper surface of this stored groundwater is called the water table.
• The water table is typically level or gently sloped but can fluctuate depending on rainfall, extraction, and other factors.
• Water Withdrawal: When a well pumps water out of an aquifer, it creates a flow of water toward the well.
• If the pumping rate exceeds the natural replenishment rate (recharge) of the aquifer, the water level near the well decreases.
• This causes the water table to drop in the immediate vicinity, forming a cone-shaped depression around the well.
• Rate of Extraction vs. Recharge: For a cone of depression to form, the rate of water withdrawal must be faster than the natural rate at which groundwater replenishes the aquifer.
• This imbalance can occur in areas where water extraction is high, such as agricultural irrigation or urban water supply systems, and where groundwater recharge (from rain or nearby bodies of water) is slow.
• Shape and Size of the Cone: The depression formed will have a conical shape, with the deepest part at the well itself.
• The size and depth of the cone depend on the volume of water being extracted and the characteristics of the aquifer.
• For example, if a well is pumping water too quickly, the cone of depression may widen and deepen as the surrounding groundwater flows into the well faster.

Additional knowledge:

• A stream flows into a sinkhole: This describes a different geological process, often related to karst topography, and does not create a cone of depression.
• Water in the zone of aeration is replaced by water from the zone of saturation: This statement describes how water naturally moves through the ground, but it is not the event that creates a cone of depression.
• A spring forms where a perched water table intersects the surface: This describes the formation of a spring, which is a natural discharge of groundwater, not a result of human-induced over-pumping.

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