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Karst Topography
The formation of caves and other associated
features in limestone bedrock is called karst
topography.
Limestone, a sedimentary rock made mostly of the
mineral calcite and small amounts of clay, is
relatively easy to dissolve with dilute acids,
including the weak dilute acid formed when
carbon dioxide dissolves in water.
Karst Topography
In order to understand karst topography we must
first have a basic understanding of the water
cycle, the formation of limestone (carbonate)
rocks and the geological processes that cause
limestone rocks to be near the surface.
Having limestone rocks near the surface in
Minnesota means we are talking about the
driftless area so a basic review of glacial geology
will be necessary.
Karst Topography
Once we know how things work we will take some
time to appreciate what has happened cause some
of the wonderful and beautiful structures
associated with karst topography.
Karst topography also presents unique
environmental problems. We will consider some
of these and discuss ways to deal with the
problems or potential problems.
The Water Cycle
The Water Cycle
Water travels through the cycle once in about 10
days. It doesn t matter where we start:
1.  Evaporation - Water molecules gain energy
from the sun (mostly over the oceans) and
change from liquid to gas. 2.  Warm, moist air will rise in the atmosphere
because it is less dense - it floats. As it rises the
air (including the water molecules) cool.
Cooling water vapor causes it to condense or
change into a liquid.
The Water Cycle
3.  Condensing water vapor causes clouds and
eventually precipitation in the form of rain or
snow.
4.  The precipitation collects on the ground in lakes
and rivers where it eventually runs off into the
oceans.
Detours in the Water Cycle
Not all of the water is directly involved in the main
water cycle. Water can be taken out of the cycle when it
precipitates as snow and is accumulated in snow
pack or glaciers.
Water can by pass runoff when plants and animals
release water vapor in transpiration.
Water can be added to the water cycle when snow
or ice melts or when ground water is pumped to
the surface.
Detours in the Water Cycle
Water is also taken out of the Water Cycle when it
infiltrates - soaks into the ground.
Of course, evaporation doesn t only happen over
oceans, it happens everywhere but the vast
majority of water vapor is from water
evaporating over the oceans.
A minor contribution to water vapor is when snow
and ice sublime - change directly from a solid
form to the gas form.
Groundwater
Ground water is defined as water that is under the
surface of the earth, trapped in porous rock and is
able to move through connecting openings in the
rock.
Because ground water slowly moves through the
connected openings it gets filtered, removing
many impurities and contaminants.
Soil Profile
Soil Profile
Typical soil has three main parts called horizons
A.  The top part, composed mostly of decayed
organic matter (plant and animal) B.  The middle part, composed of highly weathered
material - often clay.
C.  The bottom part, composed of slightly
weathered material. Groundwater
Groundwater
The zone of aeration is the ground where it is not
saturated with water. There is air in the spaces
between rock or soil. This does not mean there is
no water, only that more water could be trapped
here.
The zone of saturation is where the ground has no
spaces filled with air. All of the available space is
filled with water. The line between these zones is called the water
table.
Groundwater
At the bottom of the zone of aeration is the capillary
fringe. This is a place where water from the zone
of saturation rises up into the spaces by capillary
action. Water Table
Ground Water
Porosity is the measure of the amount of spaces in
the rock or soil that the water could occupy.
Permeability is the measure of how fast the water
can move between the interconnected spaces.
Large volumes of saturated and permeable rock or
soil are called aquifers. Aquifers are the source of well water.
A spring forms where the water table connects with
the ground surface.
Spring
Sink Hole
Springs are common in areas with Karst
Topography. Rivers erode into the limestone
bedrock causing deep valleys that interconnect
with the water table.
The opposite of a spring is a sink hole.
Sink holes are direct openings, almost a funnel,
where surface water can run directly to the water
table.
Sink Holes & other Karst Features Karst Topography
Winona State Geology
MN Sink Holes
Other resources:
1. Find the hand out from the Minnesota Geological
Survey titled Caves in Minnesota . Pay
particular attention to Figure 3 – Karst drainage
and Figure 4 – evolution of sinkholes.
Environmental Concerns
What unusual concerns about the environment
(pollution) are related to Karst Topography?
http://www.pca.state.mn.us/water/groundwater/
karst.html