Lakes

Definition: Open-surfaced stagnant water that fills a depression that is closed from every                       

                  side.

I.                   Basins formed by endogene (internal) forces

1.)    Trench lakes:

-  Faulting, breaking and divergent tectonic activity is characteristic to their formation.

      -  Shape: prolonged, long, they are very deep.

      -  The deepest lakes of the world belong to this group: Lake Baykal, Lake

          Tanganyika, Lake Nyasza

            -  the largest lake system formed by tectonic processes is located in the East- African

               trench (e.g. Albert, Nyasza, Kivu, Turkana /previously Rudolf/)

            - the trench system continues int he so-called Sirian trench and the Dead Sea is also

               here (this is a salted lake and it has the water table that is located at the lowest of all

               lakes in the world)

            - Among the Hungarian lakest he Balaton and Lake Velencei belongs here, but the

               degree of faulting was much smaller here.The deepest point of the Balaton is the

               Tihanyi fountain where the deepness is 11 m.

2.)    Lakes formed by hindrance (elgátolás) 

         The process is created by landslide (hegycsuszamlás) or slope (lejtő). E.g. Lake 

         Gyilkos (formed in 1837, the Békás stream was hindered)

3.)    Volcanic lakes (crater lakes)

          They formed in the craters of non-operating volcanoes and by the accumulated

          lakes of calderas. E.g.: Lake St. Anne àthe crater lake of Csomád

II.                Basins formed by exogene (external) forces

1.)    Glacial lakes (formed by ice)

A.)  lakes formed by the inland ice cover (belföldi jégtakaró)

           - Based on the movement of the ice and the quality of rocks on the wavy

             surface lakes can be formed. The broken-down pieces of the withdrawing

             (visszahúzódó) ice cover (àdead ice) after melting filled up the forming

             basins. E.g. the lakes of the Finnish and Canadian lake district

           - There are lakes which are located at the border of the earlier inland ice

             cover. They are in the depressions caused by the difference of level

             between covered and uncovered ancient shields. E.g.:  Lage Great Bear,

             Lake Slave, Lake Winnipeg, Lake Lagoda & Lage Onyega

           - lakes hindered by a moraine

             The moraine accumulated by ice obturate (elrekeszt) lakes. E.g.: the lakes

             of the eastern part of the German-Polish plain.

      

B.)  Lakes formed by glaciers (gleccserek)

         - tarn (kártó vagy tengerszem)

              The basins of these lakes are located in mountains, in large height. In the

              corries, which contain glacier ice, ice can accumulate and after melting

              small-surfaced, cold ponds are formed. E.g. in the high regions of the

              Alps and the Carpathians; lakes of the Higher Tatra

       - fjord lakes

             In the Ice Age the snow line was much lower than nowadays. Glaciers

             came down deeply into the valleys. Due to the warming following the

             Ice Age and the formation of today’s climatic situation the glaciers end

             higher. In the left glacier valleys, behind the accumulated moraine basins    

             formed. E.g.: lakes forming ont he northern and southern slopes of the

             Alps: Lake Garda, Lago Maggiore. It is not totally true for Lakes Boden

             And Geneva, because in their formation mountain formation also had rule.

2.)    Basins formed by rivers

                         The characteristic form of oldalazó szakaszjelleg is the ox-bow lake.

                          E.g.: lakes near River Tisza, Lake Szelidi

3.)    Lakes formed by wind

A.)  lakes formed by blowdown (kifúvás), hindrance (elgátolás)

Wind forms ponds (tavacskák) by blowdown according to the

dominant direction of wind.

4.)    Carstic lakes   

A.)  doline lakes: basins formed because of the watertightal material (vízzáró

                            anyag) of the carstic depressions. E.g.: Lake Vörös on the

                            Aggteleki-karszt

B.)  At the limestone areas obstacles (gátak) form due to the aggregation of

limestone (mészkőkicsapódás) and these form lakes. E.g.: Plitvicei lakes

      5.) Lakes formed by fauna & flora             

               A.) The atoll, which consists of coral limestone, sorrounds the lagoon and it losts

                     the connection with the sea.

               B.) Lakes obturated by beaver (hód által elrekesztett tó)

III.             Lakes formed by cosmic effect

                Lakes can be formed by meteor impacts, but there are few lakes of this type

                E.g.: Lake Titicaca (in the Andes)

IV.             Antropogene (formed by man) artificial lakes

                 Artificial lakes – can be formed with energetic, fishery and agricultural

                 purpose.

                 Reservoirs can be mountaineous (Rakacai reservoir) or síkvidéki (Lake Nasser,

                 Lake Tisza)

Degradation of lakes:

Reasons: - running out of water (climatic reason)

- cease of its basin

                     

1.)    by drainage

2.)    by filling up: - alluvium (hordalék) à E.g.: Lake Pannon

was filled up by alluvium (it was at the present location of

The Carpathian basin) à it formed the Great Plain (at Szeged the deposit /üledék/ is 6000 m thick)

-          by the flora  à eutrophication

The stages of filling up on the basis of vegetation:

- swamp (fertő): vegetation appears on the surface of the lake in spots (foltokban)

- marsh (mocsár): there is more vegetation on the surface than visible water table

- moorland (láp): water table is not visible, only the vegetation  

                                               

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