Groundwater forms when water infiltrates the earth's surface and collects underground. It is found in the saturated zone below the water table. Groundwater moves slowly through the pores and cracks in soil, sand, and rock. Over time, groundwater can cause erosion and dissolve limestone bedrock to form caves, sinkholes, and karst topography.

1. +
Erosion - Groundwater
…moving, transporting,
and depositing sediment.

2. +
June 27, 2013
2

3. +
Groundwater
 Water from rainfall can hit Earth’s surface and do
a number of things:
 Slowly soak into the ground: Infiltration
 Change to a gas: Evaporation
 Flow across Earth’s surface: Runoff
3
 Groundwater
 When water infiltrates earth’s surface it becomes part of the
groundwater.
 Groundwater can cause erosion

4. +
Factors affecting infiltration
June 27, 2013
4
 The intensity and duration of rainfall
 The harder and longer it rains, the less infiltration
 The water content of the soil
 Is the soil saturated, or can rainfall soak into it?
 Slope of the land
 Water will run off and not soak into a steep slope.
 Vegetation
 Vegetation can slow runoff and allow the surface
water to soak in.
 Porosity and Permeability of rock
 How easily water moves through pores (holes) in
the rock and sediment.

5. +
Groundwater
 Groundwater is the water found beneath Earth’s surface that
soaks into cracks and crevices in soil and rock.
 Once water infiltrates the ground, it collects below earth’s
surface as groundwater.
 There are 3 layers:
 Zone of aeration: layer of rock and soil above the water table
where pores in rock and soil are NOT filled with water.
 Water Table:The upper limit to the zone of saturation (like the
surface of pool water).The water table follows the shape of the
land.
 Zone of saturation: Layer of rock and soil pores are completely
filled with water (saturated).
5

6. +
Groundwater anatomy
June 27, 2013
6

7. +
June 27, 2013
7

8. +
How Groundwater Moves
 Groundwater does not move like an underground stream.
 Movement of water is very slow (mm/km per year).
 Gravity moves the water from high water table to low
water table.
8

9. +
June 27, 2013
9

10. +
How Groundwater Moves
10
 Groundwater often flows into streams, lakes, and out onto
earth’s surface as springs.
 Groundwater can even move up against gravity due to fluid
pressure under earth.

11. +
Factors influencing the storage and
movement of groundwater.
 Porosity:
 Amount of empty space or holes in sediment and rock that can
be used to store water.
 Depends on the size, shape, and packing of sediments in rock
and soil.
 The larger the sediments and the more sorted they are – the
more space to hold water.
 Permeability:
 How easily water flows through sediment and rock.
 Large pores = fast movement = highly permeable.
 Small pores = slow movement = highly impermeable.
 Clays have unconnected pores that do not allow water to travel
through it as well as sand and gravel.
June 27, 2013
11

12. +
Porosity – Low vs. High
12

13. +
Well sorted vs. Poorly sorted
Porosity
June 27, 2013
13
Large pores =
Fast movement =
More erosion.
Small pores =
Slow movement =
Less erosion.

14. +
Common Groundwater Features
 Aquitards
 Layer of soil or rock that are impermeable.
 Usually layers of clay.
 Groundwater cannot pass through.
 Aquifers:
 Layers of rock and soil that are highly permeable.
 Usually sand and gravel.
 Groundwater can pass through easily.
14

15. +
Common groundwater features
 Springs:
 Occur when the water table intersects with Earth’s surface.
15

16. +
Common groundwater features
 Wells:
 To obtain water by drilling through the water table into the zone
of saturation.
 The water table rises and falls throughout the year as conditions
change from dry to wet.
 The drier it is, the lower the water table = water levels in wells
are lower.
 The wetter it is, the higher the water table = water levels in
wells are higher.
16

17. +
Common groundwater features
17
Cone of Depression
 When too many wells are dug in the same area, the water table can also go
down.
 It creates a dip in the water table.

18. +
June 27, 2013
18

19. +
Common groundwater features
 Artesian Wells:
 A free flowing well where water rises on its own.
 Created by pressure produced when water is trapped between
two impermeable layers.
19

20. +
AQUIFER
June 27, 2013
20

21. +
Common Groundwater Features
 Carbon dioxide trapped in the soil
can dissolve into the groundwater.
 Water and carbon dioxide combine
to form carbonic acid.
 The groundwater then becomes an
acidic solution.
 The carbonic acid dissolves and
carries away rock underground.
 This process is called dissolution.
 Usually the weakest rock, such as
limestone or dolomite erodes the
fastest.
 Limestone deposits form overtime
from the shells and skeletons of
ancient marine organisms.
21

22. +
Common Groundwater Features
 In some cases, so much limestone
is dissolved and eroded away that
a cave begins to form.
 Given enough time, this process
can result in massive underground
caverns and rivers.
 Sequence of cave development:
 Groundwater fills open joints
through infiltration in the process of
dissolution.
 The cave passage grows larger
where more erosion occurs, creating
the most favorable flow route.
 As the water drains, deposition of
carbonate formations are left
behind on the cave walls.
 The water continues to flow on the
floor of the cave
 Continued deposition of carbonate
on the walls and floor create cave
formations. June 27, 2013
22

23. +
June 27, 2013
23

24. +
Cave Formations
 Caves are often lined with cave formations
 This occurs when limestone dissolved in water seeps through
cracks in the rock walls and is re-deposited as flowstone and
dripstone.
24
 Cave Formations
 Flowstone is precipitate from
flowing water.
 Dripstone is precipitate from
dripping water.
 A drop of water collects at the
end of a growing stalactite.
 As the water loses carbon
dioxide, a tiny amount of
calcium carbonate precipitates
from solution and is added to
the formation.

25. +
Cave Formations
 Stalactites:
 Icicle-like forms of dripstone hanging from
the ceiling of caves.
 Stalagmites:
 Blunt mounds projecting upward from the
cave floor as the water dripped onto the
floor of the cave.
 Columns:
 Stalactites and Stalagmites that join together.
25

26. +
Sinkholes and Karst Topography
 In some regions, underground valleys and
caves are fairly common.
 As the limestone or dolomite is dissolved by
acidic groundwater, layers of earth are
hollowed out to form caves.
 Often times, after a cave has formed, the
ground above it is weakened.
 Sinkholes are formed when the roof of a
cave collapses due to the dissolution of rock
near Earth’s surface.
 The right environment of acidic soil, usually
layers of limestone or dolomite bedrock,
and rainfall can produce a unique type of
landform called karst topography.
 Karst topography can be dangerous.The
dissolved bedrock can be weakened and
can suddenly collapse, creating a sinkhole.
26