Understanding Earth’s Hydrosphere: Oceans, Rivers, and Glaciers
The Hydrosphere: Earth’s Waters
The hydrosphere encompasses all of Earth’s water.
Approximately 70% of the Earth’s surface is covered by seawater, primarily in oceans and seas.
The remaining water is found in inland rivers, lakes, groundwater, and glaciers.
Marine Waters
Marine waters differ from inland waters due to their salinity. The average salinity of the oceans is 35%. Oceans are large bodies of saltwater.
Major Oceans
- Pacific Ocean: The oldest and largest ocean, characterized by its great depth and numerous island groups.
- Atlantic Ocean: Features a submarine ridge in its central part.
- Indian Ocean: Contains underwater ridges emerging from the Falkland Islands, Lakshadweep, and Seychelles.
- Arctic and Antarctic Oceans: Unlike other oceans, they have lower temperatures and salinity, and the presence of ice.
Seas
Seas are less extensive than oceans and may or may not be connected to them.
Types of Seas
- Open Seas: Have extensive communication with the oceans.
- Enclosed Seas: Have limited or no communication with the oceans.
- Island Seas: Located between the coasts of continents and island groups.
- Mediterranean Seas: Almost completely surrounded by continents and communicate with oceans through straits.
Sea Ice
Sea ice is found in the Arctic and Antarctic regions. It forms a thin layer over the sea during winter.
Movements of Water
There are three primary types of water movements:
- Waves: Oscillating movements of sea surface waters caused by wind action.
- Tides: Periodic rise and fall of sea level caused by the gravitational attraction of the sun and moon.
- Ocean Currents: Displacement of ocean surface waters that maintain a consistent direction.
Rivers
A river is a stream of fresh water that moves over land along a slope. The channel through which the river flows is called the bed, and the deepest part is the thalweg. The flow of river water is measured in cubic meters per second, and this flow can vary throughout the year, a variation known as the regime.
River Regimes
- Regular Regime: Exhibits little to no variation in flow.
- Irregular Regime: Can be influenced by snowmelt (increasing flow during thawing) or rainfall (with winter or summer precipitation).
- Mixed Regime: Exhibits a double peak in flow.
When a river reaches a sea or lake, it drains. If the waters drain into an open sea, it is called exorheic drainage. If the waters drain into enclosed seas or lakes, it is endorheic drainage. Water can also be lost through evaporation or infiltration.
Lakes
Lakes are bodies of water of varying volume and surface area located in a depression.
Types of Lakes
- Tectonic Lakes: Usually have elongated shapes and considerable depth.
- Glacial Lakes: Formed when erosive forces disappear and the resulting depressions are filled with glacier water.
- Tectonic-Glacial Lakes: A combination of tectonic and glacial processes.
- Volcanic Lakes: In some cases, the crater is blocked by hardened lava, resulting in water accumulation from rain or snow.
- Relict Lakes: Remnants of ancient seas.
- Artificial Lakes: Man-made reservoirs.
Subterranean Waters
Subterranean waters originate from rainwater, snowmelt, and infiltration into permeable ground. When they encounter impermeable layers, they move along the gradient.
Glaciers
Glaciers originate from successive accumulation, compaction, and freezing of snow.
Types of Glaciers
- Continental Glaciers: Cover large areas of land, such as Antarctica.
- Sea Glaciers: Include ice barriers, icebergs, and pack ice (frozen sea surface).
River Basins
A river basin is the area covered by the main drainage system, including tributaries and the land between them. It encompasses all rivers joining the main drainage channel. The river at the mouth of the basin gives its name to the basin.