The ice age

What is an ice age?

 An ice age, or an glacial period, is a results of a colder climate, which cause large landareas to be covered by ice. Between these ice ages ”interglacials”, or warmer periods, occur. It is believed that we now exist in an interglacial period. The first ice age was about 2,4 million years ago, and for the last .600 000 years earth has had three ice ages; Elster, Saale and Weichsel. The last ice age, Weichsel, started about 115 000 years ago and ended about 10 000 years ago.

Ice sheet

 

 

 

 

 

 

 

 

 

 

 

 

 

Picture: Spread and thickness of the glacial ice over Scandinavia during the last ice age.

Ice ages leave tracks in the environment, as sediment deposits, rock scouring and scratching, which indicate the direction of the moving ice, and different types of moraines. Most apparent are the traces from the last ice age Weichsel.

The Kvarken archipelago

The bedrock of the Kvarken area consists mainly of rock as old as 1800-1900 million years, with segments of younger rocks. The oldest rocks are metamorphic rocks, formed out of sand and mud, as mica gneisses, vein gneisses, amphibolites, as well as kind of diatextite called Vaasa granite. They also mixed with granodioritic melts.

 Some 1800 million years ago a new heat pulse influenced bedrock development by creating granitic melts in the Eastern parts of Kvarken and pegmatites (a coarse grained granitic rock) in the western parts. A tectonically quiet time followed and lasted until 1570 million years ago when the Rapakivi magmas rose and began to crystallize in the upper parts of the crust. During Rapakivi magmatism also diabases and gabbros intruded the bedrock.

The current form of the landscape is a result of the end of the ice age about 24 000 to 10 000 years ago. Moranes – a mix of boulders, rocks, gravel, sand and silt- deposited by the ice, covered the now smoothened bedrock and the Kvarken landscape is now dominated by charectaristic moraine formations. On the Finnish side of the archipelago ridges of De Geer and Ribbed moraines, deposited in the direction of the efge of the ice cap, are common. On the Swedish side, on the other hand, the landscae is dominated by drumlins which are consistent with the course of the ice. Other examples of traces of the last ice age that can be seen in the Kvarken archipelago are scratchings in rocks and cobble fields, also called ”the devil´s fields.

 The land upflift together with the force of the waves have later caused further changes in the landscape, as well as changed the conditions of vegetation and other living creatures.