From ice sea to lake Horn­bor­ga­sjön – Around 13,000 years ago the ice had mel­ted and lake Horn­bor­ga­sjön was a shal­low bay in the sal­ty Väs­ter­ha­vet sea. As the weight of the ice was remo­ved, the land slowly began to rise. Soon the bay beca­me iso­la­ted from the sea and Horn­bor­ga­sjön beca­me an inland lake.

Over the thousands of years that have pas­sed sin­ce then, the cli­ma­te has alter­na­ted from warm and dry to cold and wet. The size of Horn­bor­ga­sjön has swel­led and shrunk. But over time the lake has become shal­lo­wer and shallower.

You can still see tra­ces of the mas­si­ve inland ice she­et in the lands­cape today. Insi­de and bene­ath the ice, mighty rivers raged. The­se rivers in the ice left behind eskers – win­ding ridges of sto­nes, gra­vel and sand. Near Horn­bor­ga­sjön you can see ridges of this type at Väs­storp­så­sen and Ore. Their steep slo­pes are due to the fact that they lie abo­ve the hig­hest point of the sho­re­li­ne, so they were never ero­ded by sea waves. Becau­se of their shape they are known as hog­back ridges. In some loca­tions ice lakes were for­med as the ice mel­ted. The­se lakes could be drai­ned very sud­den­ly when the water bro­ke out and flooded the lands­cape with gre­at vio­lence. The Horn­bor­ga­ån river val­ley was cre­a­ted as a result of the drai­ning of such ice lakes to the east.

 Thanks to the tab­le mountains, lake Horn­bor­ga­sjön lies in a bowl-sha­ped depres­sion. This allows ther­mal updraughts to deve­lop here, as the trap­ped air is hea­ted and starts to rise. Birds often take advan­tage of the­se ther­mals to climb to hig­her alti­tu­des. This saves a gre­at deal of ener­gy for cra­nes and birds of prey.

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Horn­bor­ga­sjön is a natu­re reser­ve.