Notes: Ch 14 Groundwater
Groundwater is a part of the water cycle. After it rains, the water either runs off or infiltrates the
ground. There’s an increase in runoff with urbanization and a decrease in infiltration
Groundwater is simply water under the ground where the soil is completely filled or saturated
with water. Rock that carry groundwater in enough quantity to supply wells are called aquifers.
Groundwater moves underground from areas where the elevation is high, like a hilltop, to places
that are lowland areas. Movement is slow and might move anywhere from less than 1mm. up to
1mi. in a day.
Where the water table meets the land surface, a spring
might bubble up or seep from the ground and flow into
a lake, stream, or the ocean.
Ground water that meets the land surface also helps
keep rivers, streams, lakes and wetlands filled with
water.
Zone of Aeration: area where the pore spaces in the rock/soil are filled with
air
Water Table: boundary between zone of saturation & zone of aeration;
wells must be dug below the water table to reach water.
Zone of Saturation: area where the pore spaces in the rock/soil are
saturated or filled completely with water.
Permeability: how quickly water can travel through a material
Porosity: the percent of a material’s volume that is pore space
Notes: Ch 14 Caves
Limestone is a common bedrock that dissolves more easily than some types of rock. The
carbonic acid found in groundwater dissolves the calcite found in limestone. Chemical
weathering changes the calcite into clay increasing the porosity of the limestone left behind.
Over time as more and more water flows through cracks in the limestone bedrock, the carbonic
acid dissovles the limestone and carries it away in solution. After thousands of years, these
cracks become larger eventually forming a network of tunnels. These caverns or caves can be
many miles long and hundreds of feet deep.
Cave Formations
When water drips from the roof of a cave, calcite is
deposited. Slender deposits called stalcitites hang like
icicles from the roof. On the cave floor beneath them, a
rounded mass called stalagmites form. When they
meet, a column is formed.
Karst Topography
They are regions characterized by caves, sinkholes, lost rivers or sinking streams, and
underground drainage.
Karst Topography forms in areas with bedrock made of calcite like limestone (or dolomite).
Development of Karst Topography
1.
2.
3.
Step 1: Groundwater dissolves limestone bedrock. Then the water table drops, leaving empty caves.
Step 2: Ground above the caves is eroded away.
Step 3: Thin rock above the cave collapses, forming a sinkhole.
Because rainwater drains through sinkholes, there are few
surface rivers in Karst regions.
Lost rivers form when the surface stream disappears
underground and flows out of a cave many miles away.