ground water_groundwater as geological agent.pptx

Groundwater is the water that occupies the pore spaces and fractures of rocks and soils beneath the Earth’s surface, forming one of the most vital natural resources on which both ecosystems and human societies depend. Unlike surface water bodies such as rivers, lakes, or streams, groundwater is stored in subsurface zones and moves slowly through porous media, often invisible to the human eye yet playing an indispensable role in the hydrological cycle. It originates primarily from the infiltration of precipitation, where a portion of rainwater seeps into the soil, percolates downward past the root zone, and accumulates in the saturated zone below the water table. The subsurface environment is generally divided into two zones: the unsaturated zone, where pore spaces contain both air and water, and the saturated zone, where all voids are filled with water. Aquifers, the geologic formations that store and transmit groundwater, are categorized as unconfined, where water is directly recharged by surface infiltration, or confined, where impermeable layers trap water under pressure. The quality and quantity of groundwater depend on the geological characteristics of the aquifer, recharge rate, and human influences. Permeable formations like sandstone, limestone, and unconsolidated sediments tend to be good aquifers, while clay and crystalline rocks often act as aquitards or aquicludes that restrict water flow. Groundwater movement is typically slow, ranging from a few centimeters to a few meters per day, controlled by hydraulic gradient and permeability. Despite its slow flow, groundwater is essential for maintaining baseflow in rivers and streams, especially during dry seasons, and for sustaining wetlands and terrestrial ecosystems. It is also one of the primary sources of freshwater for human use, accounting for more than a third of global drinking water supplies and supporting irrigation, industry, and municipal demands. Historically, civilizations have tapped groundwater through wells and springs, and modern pumping technology has dramatically increased reliance on aquifers worldwide. However, excessive groundwater extraction leads to severe consequences such as aquifer depletion, land subsidence, saltwater intrusion in coastal areas, and reduced river flow. Pollution from agricultural chemicals, industrial effluents, and untreated sewage further threatens groundwater quality, as contaminants can persist for decades due to the slow rate of groundwater renewal. Natural geogenic contaminants, such as arsenic and fluoride, also pose serious challenges in many regions, making groundwater safety a major concern. In arid and semi-arid regions, groundwater often represents the only reliable water source, yet it is typically fossil water—recharged thousands of years ago and not easily replenished. Sustainable groundwater management therefore requires balancing withdrawal with recharge, protecting recharge zones, preventing contamination, and adopting integrat

1. Erosion and deposition by ground water Caves Sink holes Karst topography Petrification Cementation

2. CaCO 3 + H 2 CO 3 ------------> Ca 2+ + 2HCO3 - Caves Dissolution of limestones , caves develop. Caves have many shapes and sizes. A very large cave or system of inter-connected caves is called cavern .

3. Stalactites The deposits formed by the precipitation of calcium carbonate, hanging from the ceiling of the cave is called stalactites. They are also called dripstones

4. Stalagmites The deposits of calcium carbonate formed at the floor of the cave is called stalagmite . Column As the two features continue to grow, they may eventually join to form a column . Speleothems Collectively , all mineral deposits formed by water in caves are called speleothems .

5. Sinkholes If the roof of a cavern collapses, a sinkhole forms on the Earth’s surface. A sinkhole can also form as limestone dissolves from the surface downward. They are usually funnel shaped.

6. Karst topography Karst topography forms in broad regions underlain by limestone and other readily soluble rocks. The landscape is characterized by numerous sink holes and beneath the land surface a cave system. Surface streams often pour into sinkholes and disappear into caverns . The word karst is derived from a region in Croatia where this type of topography is well developed.

7. Petrification In some places, water dissolves matter already present in the substance and deposits ions of another substance (which was carried by the ground water) on equal volumes. This process is called petrification or replacement. Petrified wood is formed when the organic matter of buried wood is replaced by inorganic silica carried by ground water.

8. Cementation Ground water carries different cements like CaCO3 or silica and precipitates in the interstices between the grains of sedimentary rock, reducing the porosity. Sometimes a hard round mass called concretions develop. The concretions are also known as nodules . The nodules are grown around nucleus such as leaf, tooth, or other fossil. They range in size from fraction of an inch to many feet in diameter. Usually concretions are made of silica (SiO2), CaCO3 or iron sulphate.

9. Geodes Geodes are partially hollow, globe shaped bodies found in limestone and occasionally on other rocks. The outer shell is of silica and well-formed crystals of quartz or calcite project and grow inward towards a central cavity.