Chapter 9: Hydrologic Cycle and Weathering

99% of Earth’s moisture is in

oceans, lakes, rivers, glacial ice, or rocks beneath the surface

hydrosphere

• oceans = 97.2%

• nonocean = 2.8%

  • glaciers = 2.15%

  • groundwater = 0.62%

1% of Earth’s moisture is

involved in a continuous sequence of movement and change called the hydrologic cycle

3 primary movement types

1.) Surface to air

2.) Air to surface

3.) Beneath the surface - runoff

surface to air movement

• ocean evaporation

• vapor remains in air for a short time

air to surface movement

• precipitation - 78% falls on oceans, 22% falls on land

• precipitation is the same as evaporation over long time scales

beneath the surface movement - runoff

• water collects in lakes and rivers and either penetrates the ground or runs off if sloped

• becomes part of underground water supply

• reemerges as springs or becomes part of rivers and streams

residence time

the average amount of time water spends within a specific reservoir, such as a lake, ocean, or atmosphere, before it moves to another reservoir

4 principal parts of the oceans

1.) Pacific → largest, occupies 1/3 of total Earth surface area

2.) Atlantic → less than half the size of the Pacific

3.) Indian → slightly smaller than Atlantic

4.) Arctic → small and shallow

smaller bodies of water

seas, gulfs, and bays

chemical composition of oceans

sodium and chlorine → salinity (affects density)

increasing acidity of oceans

• CO₂ absorbed by ocean water creates carbonic acid

• affects the ability of microscopic creatures to build shells and exoskeletons

temperature of oceans

• decreases with increasing latitude

• ranges from near 80ºF to near 28ºF

density of oceans

• high temp = low density

• high salinity = high density

currents of oceans

subtropical gyres develop from surface wind patterns

causes of tide

• gravitational attraction of moon (lunar tides) and sun (solar tides)

• more gravitational force on the side of Earth facing the moon

• more centripetal force on opposite side to keep Earth in orbit

• 2 bulges form on opposite sides of the planet

tides - 2 cycles every 24 hours

• flood / high tide

• ebb / low tide

tides - monthly tidal cycles

• spring tides

• neap tides

tidal range

difference in high and low tides

the cryosphere

permanent ice - the second greatest storage of water

• ice on land and in/on water

• approximately 10% of Earth’s surface is ice

permanent ice

• largest ice pack covers most of the Arctic ocean surface

• several large ice shelves attached to Antarctica

• large ice floes form off Antarctica

• permafrost

permafrost

permanently frozen ground ice

more than 50% of the world’s underground water is found

within 800 meters of the surface

underground water quantity depends on 2 things

1.) Porosity

2.) Permeability

porosity

the percentage of the total volume of the material that consists of voids (pore spaces or cracks) that can fill with water

permeability

the ability to transmit underground water (as opposed to just hold it), determined by the size of pores and by their degree of interconnectedness

aquiclude

an impermeable rock layer that is so dense as to exclude water

aquifer

a permeable subsurface rock layer that can store, transmit, and supply water

zone of aeration

the topmost hydrologic zone within the ground, which contains a fluctuating amount of moisture (soil water) in the pore spaces of the soil (or soil and rock)

zone of saturation

the second hydrologic zone below the surface of the ground, whose uppermost boundary is the water table - the pore spaces and cracks in the bedrock and the regolith of this zone are fully saturated

groundwater flows the same way that

surface water flows (based on topography)

waterless zone

at some depth below the surface, the overlying pressure on the rock is so great that there are effectively no pore spaces, and so the rock here cannot hold or transmit groundwater

groundwater mining

• accumulation of groundwater is slow, but human use is rapid

• ex. Ogallala aquifer

Ogallala aquifer

• water table drops with increased use

• numerous wells, unsustainable situation

lakes

bodies of water surrounded by land

• saline/freshwater lakes

• ephemeral lakes (only contain water sporadically)

• most are relatively short-lived

2 conditions required for lake formation

1.) Natural basin with restricted outlet

2.) Sufficient water to keep basin filled

3 examples of human alteration of natural lakes

1.) Irrigation

2.) Water diversion projects

3.) Reservoirs

reservoirs

artificial lakes used for hydroelectric power, municipal water, and stable agriculture

swamps and marshes

• flattish places periodically submerged

• shallow enough for plant growth

• swamps grow trees

• marshes grow grasses and rushes

rivers and streams

• streams are smaller than rivers

• geographers call all running water streams

• allow for drainage of land surface water towards oceans

• drainage basins/watersheds