Origins
Lecture Lake 2 Fall 2011
BIOL/EVPP 350
Freshwater Ecosystems
Dr. Kim de Mutsert
Lake Basins
The lake basin is the bowl or depression that
contains the water
Lake basins are formed by numerous
processes, the principal being:
1.Glacial activity
2.Tectonic/Crustal movement
3.Volcanic action
4.Solution processes
5.Fluviatile/riverine processes
6.Animal/human activity
1.Lakes formed by Glacial Processes
Glaciation is a major geological process that forms lakes
Continental glaciers are slowly moving and melting ice
masses as deep as 3000 (!) meters: this weight enables
them to rework the earths surface
Glaciers create
basins for lakes by:
- dropping sediments
- leaving icebergs in
sediments
- scouring and
depressing the earths
surface
1.Lakes formed by Glacial Processes
Glacial activity has resulted in the
greatest number of lakes and
some of the largest lakes in area
Glacial lakes are found in areas of
steep terrain where scour has
been the mechanism
Lake in contact with a glacier
The lakes of Minnesota
(Land of 10,000 Lakes), the
Adirondacks in New York and
The Great Lakes are
attributable to glacial activity
Alpine Glaciation
Small mountain glaciers
advanced as recently as the
little ice age (1570-1860)
Deepening basins or
producing new ones
When filled with water, tarns
are created
Photos: Kim de Mutsert, 2006
Glacial Dams and Moraines
Piles of remnants of glacial erosive action (clay, sand,
gravel, boulders) are called moraines
Moraines can dam up valleys or rivers, thereby creating
lakes
Castle Lake, CA: cirque lake formed by glacier scour
leaving a terminal moraine at the outflow. A lateral
moraine separates a 5m deep littoral plain from a 35 m
deep bowl
Kettle ponds
Glacial till (sediments) could be mixed with large
blocks of ice
This created steep basins within the till
Northern Wisconsin Lakes
Plunging, scouring and depressing
Waterfalls of glacial meltwater have created plunge basins in
moraine deposits
Continental glaciers have scoured out large basins in bedrock
Glaciers also depress the continental surface with their weight:
the crust slowly rebounds after the glaciers melt
Hudson Bay
The Great Lakes
2. Lakes formed by Crustal Movement
Where tectonic plates meet, the surface of the Earth will
sometimes break with one plate moving downward relative
to the other
The basin created by broken crust is called a graben and
can host a lake
These lakes tend to be millions of years old and hundreds
to thousands of meters deep
Grabens are often filled with a deep lake on even deeper
sediments
The broken crust often forms cliffs on the sides of a
graben lake
Graben Formation
Grabens are
depressions
formed when
land between
two faults
subsides or tilts
as the crust
moves along
the faults
The deepest and oldest
lakes in the world are
those formed by crustal
movement (Tectonic
activity)
The deepest and oldest
lake in the world is Lake
Baikal in Siberia
composed of several
interconnected grabens
Lake Baikal is a 1741
meter deep lake on top
of more than 3000
meters of lake sediments
Rift valleys
Grabens or rift
valley lakes can
occur in groups
A large number
are found in E.
Africa
Lake Tanganyika
Origin Lakes of - Tectonic
Crustal uplifting
More complex than graben
Entire section of the crust
is uplifted
Caspian Sea: formerly part
of the ocean, cut off by
crustal uplift
Lake Okeechobee, FL:
similar origin, partially
maintained by damming with
plant material
Lake Titicaca, Peru
Tectonic Basins Uplifted sea
beds
Slow uplifting of ancient sea beds to form
shallow depressions
L. Okeechobee, FL
Origin of Lakes Tectonic
Earthquake Lakes
Reelfoot Lake, TNKY
Major earthquake (8
on Richter scale)
Caused surface to
uplift in some areas
and subside in
others
Mississippi R was
diverted into a
subsidence region
for several days
forming Reelfoot
Lake
3. Origin of Lakes - Volcanic
Crater/caldera Lakes
Volcanic activity produces
craters, also called
calderas, which in some
cases hold water
Crater lakes have a small
watershed and are
therefore oligotrophic
Example: Crater Lake, OR
Crater Lake, Oregon
Crater Lake- 589 m deep
(Mt. Mazama exploded)
Dates to about 6500 years
ago
Very low watershed to
http://geopubs.wr.usgs.gov/fact-sheet/fs092-02/
lake area ratio (Aw : A0)
Steep sides
Low nutrient soils
Unproductive
Extremely clear
www.cs.uoregon.edu/.../oregon/large/
Origin of Lakes Volcanic Lakes
Lava dams
Lava flow dams
an existing valley
Lake Kivu, Africa
Meromictic Lake,
contains high
conc of CO2
Could cause
suffocation if
overturned
4. Solution Lakes
Lake basins can be formed when subsurface
mineral deposits (like halite or limestone) dissolve
leaving a void which collapses resulting in a basin
Origin of Lakes Solution Lakes
Carbonate areas
Basin created by
dissolution of removal
by groundwater of
CaCO3 and MgCO3
rocks
Overlying ground
eventually collapses:
sinkhole
May lead to lakes or, if
there are seams of
carbonate, to a karst
landscape
Lakes of Central Florida
Origin of Lakes Solution Lakes
Salt collapse
basins
Underground
seepage dissolves
salt lenses, ground
collapses and basin
fills
Montezuma Well,
AZ
5. Origin of Lakes Fluviatile
(river-made)
Alluvial rivers leave behind bends
that become oxbow lakes
Oxbow lakes are localized to areas
in alluvial floodplains, like the lower
Mississippi valley
Example: False River, LA
6. Origin of Lakes Biological
activity
Humans
Intentional reservoirs
Incidental flooding of
basins constructed for
other purposes
Quarries
Peat diggings
Other agents
Beavers (dams)
Lakes formed by Human Activity
These may be intentional,
as in the case of
reservoirs created for
recreation, flood control,
irrigation, water supply
navigation, hydropower
Reeuwijkse plassen, peat bogs in the Netherlands
Reservoir in north Italy
Or they may be
incidental, as in the case
of flooded peat digs or
rock quarries or mining
pits
Origin of Lakes Lake Districts
Because most of the factors responsible for lake
origins or localized or regional, lakes tend to be
clustered in districts
Glacial Lakes: Minnesota, Wisconsin,
Ontario, New York, New England
Oxbow Lakes: lower Mississippi Valley
(Arkansas, Mississippi, Louisiana,
Tennessee)
Rift valleys (Africa)
Peat bogs (the Netherlands)
Even reservoirs are clustered due to
favorable geology, physiography, demand