60
4 °C. There could be only one circulation
period during winter.
Order 3 : In these lakes, temperature of bottom
water is very much similar to that of surface
water. Circulation could practically be continuous throughout the year.
5.2
Classifi cation of Lakes on the
basis of their Origin
Lakes are geologically transitory. They are usually born out of catastrophes occurring in nature
and die quietly (Hutchinson 1957 ). Thus, a lake
lives through youthful stage of maturity and
senescence, and death occurs when its concave
basin is fi nally fi lled up.
Classifi cation of lakes on the basis of their origin is given below.
5.2.1 Glacial Lakes
Glaciers deepen and widen the valleys when they
glide down. When the huge mass of ice melts, it
leaves piles of moraine, which blocks valleys
and, thereby, dams streams and rivers. Thus, the
scraping action of glaciers leads to the formation
of lakes. Such lakes are generally found in the
north temperate regions of the world.
5.2.2 Ice-Scour Lakes
When huge sheets of ice move over relatively
fl at surfaces of hard, jointed or fractured rocks,
scours or hollow basins are formed. Later,
these hollow basins are fi lled with water resulting in lakes.
5.2.3 Tectonic Lakes
Lakes formed by movements of earth’s crust (tectonic plates) are called tectonic lakes. When a
portion of the earth’s surface subsides in relation
to its surroundings or, conversely, when a portion
of the earth’s surface is lifted, a lake is formed.
The area and depth of water in the newly formed
lake will depend on the drainage pattern from the
surrounding catchment, which, in turn, depends
on the amount of rainfall and the size of the area
from where water drains into the lake.
5.2.4 Volcanic Lakes
Lakes which are formed due to volcanic eruptions are called ‘crater lakes’. They are formed
when a series of minor eruptions take place fairly
close to each other. In instances where the volcano was big and had erupted long ago, the fl oor
of the huge crater of such volcanoes is relatively
fl at; and water accumulates in some of the deeper
zones, resulting in the formation of lakes. Further,
volcanic activity could also form a lake when the
ash or lava from an eruption blocks natural
drainage.
5.2.5 Riverine Lakes
River-formed lakes, i.e. the lakes formed by the
action of rivers, are commonly called riverine or
‘oxbow’ lakes. Bank erosion is quite fast in fastfl owing tortuous river. At one point of time, the
river breaks through the continually eroded narrow isthmus between two successive curves. This
may leave a loop of the river to one side of the
new watercourse. This isolated portion may
retain enough of water to form an oxbow lake.
5.3
Classifi cation of Lakes
on the basis of Circulation
and Mixing
On the basis of circulation and mixing, the lakes
could be of the following kinds (Hutchinson
1957 ):
5.3.1 Monomictic Lakes
Lakes in which there is one only one mixing are
called monomictic lakes
5 Lakes in the Landscape, Their Classifi cation, Origin, Evolution
4 °C. There could be only one circulation
period during winter.
Order 3 : In these lakes, temperature of bottom
water is very much similar to that of surface
water. Circulation could practically be continuous throughout the year.
5.2
Classifi cation of Lakes on the
basis of their Origin
Lakes are geologically transitory. They are usually born out of catastrophes occurring in nature
and die quietly (Hutchinson 1957 ). Thus, a lake
lives through youthful stage of maturity and
senescence, and death occurs when its concave
basin is fi nally fi lled up.
Classifi cation of lakes on the basis of their origin is given below.
5.2.1 Glacial Lakes
Glaciers deepen and widen the valleys when they
glide down. When the huge mass of ice melts, it
leaves piles of moraine, which blocks valleys
and, thereby, dams streams and rivers. Thus, the
scraping action of glaciers leads to the formation
of lakes. Such lakes are generally found in the
north temperate regions of the world.
5.2.2 Ice-Scour Lakes
When huge sheets of ice move over relatively
fl at surfaces of hard, jointed or fractured rocks,
scours or hollow basins are formed. Later,
these hollow basins are fi lled with water resulting in lakes.
5.2.3 Tectonic Lakes
Lakes formed by movements of earth’s crust (tectonic plates) are called tectonic lakes. When a
portion of the earth’s surface subsides in relation
to its surroundings or, conversely, when a portion
of the earth’s surface is lifted, a lake is formed.
The area and depth of water in the newly formed
lake will depend on the drainage pattern from the
surrounding catchment, which, in turn, depends
on the amount of rainfall and the size of the area
from where water drains into the lake.
5.2.4 Volcanic Lakes
Lakes which are formed due to volcanic eruptions are called ‘crater lakes’. They are formed
when a series of minor eruptions take place fairly
close to each other. In instances where the volcano was big and had erupted long ago, the fl oor
of the huge crater of such volcanoes is relatively
fl at; and water accumulates in some of the deeper
zones, resulting in the formation of lakes. Further,
volcanic activity could also form a lake when the
ash or lava from an eruption blocks natural
drainage.
5.2.5 Riverine Lakes
River-formed lakes, i.e. the lakes formed by the
action of rivers, are commonly called riverine or
‘oxbow’ lakes. Bank erosion is quite fast in fastfl owing tortuous river. At one point of time, the
river breaks through the continually eroded narrow isthmus between two successive curves. This
may leave a loop of the river to one side of the
new watercourse. This isolated portion may
retain enough of water to form an oxbow lake.
5.3
Classifi cation of Lakes
on the basis of Circulation
and Mixing
On the basis of circulation and mixing, the lakes
could be of the following kinds (Hutchinson
1957 ):
5.3.1 Monomictic Lakes
Lakes in which there is one only one mixing are
called monomictic lakes
5 Lakes in the Landscape, Their Classifi cation, Origin, Evolution