Download The ice age

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.
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.