Download The Lakeland Finland

THE GEOLOGY OF THE LAKELAND FINLAND
AREA
Jari Nenonen and Anne Portaankorva
Geological Survey of Finland
2009
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TABLE OF CONTENTS
1. FINLAND’S GEOLOGICAL HISTORY ……………………………………………….. 3
2. BEDROCK GEOLOGY OF FINLAND AND THE NEED-PROJECT’S REGION…… 4
3. THE BEDROCK OF THE NEED-PROJECT’S REGION ……………………………... 9
4. SURFICIAL DEPOSITS IN THE NEED-PROJECT REGION ……………………….. 13
4.1. Glacial deposits ……………………………………………………………………. 18
4.1.1. Basal till ....…………………………………………………………….…... 18
4.1.2. Ablation moraine – hummocky moraine ………………………………….. 19
4.2. Glaciofluvial deposits ….…………………………………………………………... 20
4.2.1. Eskers ……………………………………………………………………... 20
4.2.2. Ice-marginal formations …………………………………………………... 21
4.3. Aeolian deposits ………………………………………………………………….... 23
4.4. Peat deposits ……………………………………………………………………….. 24
5. EVOLUTION OF THE LAKES ……………………………………………………….. 24
6. GEOLOGICAL SITES IN NATURE TOURISM ……………………………… …….. 29
7. LITERATURE …………………………………………………………..……………... 31
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1. FINLAND’S GEOLOGICAL HISTORY
A special feature in Finnish geology is the very old bedrock and the much younger surficial deposits lying
on top of it. Finland’s geological history is extremely long. The history of bedrock goes up to 3,5 – 3,7
Ga ago when the old Archaean basement was developed(Fig. 1). The oldest stone in Finland and in the
whole of the EU is Siurua gneiss (3,5 Ga years old) near the town of Pudasjärvi in northern Finland (Fig.
2).
Surficial deposits have developed during the last two million years, during the so called ice age. Glaciers
eroded the bedrock beneath them and deposited loosened material upon it as quaternary deposits.
Bedrock, together with quaternary deposits and landforms, builds up the variable landscape complex
which can be seen today.
Figure 1. Two scales illustrating the historical development of Finnish geology by Tapani Tervo and Harri
Kutvonen, GTK.
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2. BEDROCK GEOLOGY OF FINLAND AND THE NEED-PROJECT’S REGION
THE ARCHEAN BASEMENT
The bedrock of Eastern and Northern Finland consists of ancient rocks dating back to more than 2500
million years, the detailed origins of which are not accurately known. Their development would seem,
however, to have been controlled by events in which large quantities of the earth’s crust melted and then
crystallized slowly to form various granitoids and gneisses (Fig. 3). These were interspersed with
sequences of schists, depicted in a darker shade on the map, which represent the remnants of rocks that
had once been deposited at the surface, mostly from thick, widely distributed lava flows. This Archean
area is, in effect, an ancient continent that served as a starting point for the second stage in the
development of the Finnish bedrock (Map 1).
Figure 2. The Siurua gneiss (age 3,5-3,7 Ga)
Map 1. The Archean basement
Figure 3. Gneiss
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THE KARELIDIC BEDROCK
The creation of the Archean bedrock was followed by more than 500 million years of erosion and
deposition that caused clay, sand and gravel to accumulate on top of the ancient continent and at its edges.
These gave rise in time to the quartzites, conglomerates, mica schists, mica gneisses and granulites of the
Karelidic belt (Fig. 4, 5).
During this period the earth’s crust was broken up by numerous rift valleys bounded by fault zones. The
faults were filled with molten rock, or magma, some of which crystallized deep in the crust, while some
was discharged at the surface to form sequences of volcanic rocks. These are marked in dark green on map
2. Then, about 2000 million years ago, the ancient continent split in two and the blocks drifted apart
causing the fault to develop into an ocean. It is not known what happened to the western block.
Figure 4. Ripple marks in quartzite
Map 2. The Karelidic bedrock
Figure 5.Granulite
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THE SVECOFENNIAN BEDROCK
Already about 1920 million years ago, the present area of Eastern Finland was an ancient continental land
mass covered by sedimentary rocks, with an ocean to the west of it. As a result of movements of the
tectonic plates, a number of arcs of volcanic islands arose that were thrust eastwards by flows taking place
within the earth, colliding with each other and eventually with the old Archean basement. By the time this
collision phase had come to an end around 1870 million years ago, the area of Finland was occupied by a
range of high mountains( Map 3).
The processes of folding that gave rise to these mountains, had caused the volcanic islands and their
related sedimentary rocks to be piled up against the ancient continental mass in the east. This meant that
some of the sedimentary rocks were thrust down deep into the earth’s crust, where they melted and then
slowly crystallized to form various plutonic rocks (Fig. 6, 7).
Figure 6. The Nattanen granite tor formations
Map 3. The Svecofennian bedrock
Figure 7. Koli quartzite polished by continental ice
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YOUNGER FORMATIONS
The folding that created the range of mountains was followed by a long period of erosion, so that only a
few isolated features of the Finnish bedrock have been preserved from that time. These rapakivi granite
areas are indicated in red on the map 4 (Fig. 8), while the yellow areas show the presence of sandstones
and argillites dating back 1400-600 million years. The events that gave rise to the Caledonides in Norway
about 400-450 million years ago also caused a bed of younger sedimentary rocks to thrust into the northwestern parts of the Enontekiö region of Finland. A number of kimberlite pipes of igneous origin that
contain diamonds, have been discovered in Northern and Eastern Finland (Fig.9) , and the hills of Iivaara
and Sokli are formed by alkaline igneous rocks aged 370-360 million years.
Figure 8. The Rapakivi granite, GTK.
Map 4. Young bedrock formations.
Figure 9. Diamonds and side minerals. GTK
Development of Finnish bedrock presented on same time scale.
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NEED-region
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3. THE BEDROCK OF THE NEED-PROJECT’S REGION
In the area under study, the bedrock is divided into three bedrock units of different ages. The northernmost
is the Archean gneiss area (age 3200-2700 Ma), in the center is theEarly Prorerozoic schist and plutonic
rock area (age 1900-1800 Ma) and in the south the Middle Proterozoic rapakivi area (age 1650-1570 Ma)
(Map 5) (Vaasjoki ym. 2005).
The northernmost, Archean area, belongs to Finland’s oldest bedrock area. Typical types of rocks in that
area are gneisses with greenstone periods.
The Archean mountain folding was followed by hundreds of millions of years of erosion, which involved
strong faulting and volcanism. The bedrock were splitting strongly, forming sedimentation basements and
there was also active volcanism at that time.
At the end of the splitting phase major climate changes occurred, the most significant being the increase in
the amount of oxygen ca 2100 million years ago to the current level (Karhu 1993).
About 2400 million years ago the mountain ridge was eroded into a flat peneplain. Thick sediments were
deposited on top of it about 2200 - 1970 million years ago. Sedimentation was associated with several
periods of volcanism which resulted in diabase veins cutting the Archean basement and the sediments
about 2450 - 1970 million years ago (Fig. 10) (Vaasjoki ym. 2005).
The long sedimentation phase was followed by the folding of the Svecokarelian mountains about 1900 –
1800 million years ago. The sediments were folded and metamorphosed as crystalline schists like
quartzite, phyllite and mica schist. Primary structures like ripple marks in the Koli quartzites can still be
seen in the rocks (Fig 11).
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Map 5. The bedrock of the NEED region, GTK.
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Figure 10. A series of illustrations showing the development of eastern Finland and the Koli area’s
bedrock. T. Tervo, GTK
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Figure 11. Quartzite with ripple marks. A. Portaankorva, GTK.
Tectonic movements in the earth crust’s ended about 1800 million years ago, and was followed by a long
phase of erosion. In the southernmost part of the area fine grained rapakivi rocks can be found. This
rapakivi bedrock is aged about 1640 – 1635 million years. (Simonen & Tyrväinen 1981)
During the Precambrian eon many meteorites crashed in to the earth. The big meterorite crater, Paasselkä,
can be seen today as a rounded lake in the eastern part of the area (Fig. 12) (Kuivasaari ym. 2000).
Figure 12. Paasselkä, meteorite crater. A. Portaankorva.
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Tectonic movements created fault and fracture zones in the bedrock. The Kolvanauuro and Korkiakoski
gorges are situated in these kind of fault zones (Fig 13, 14). Later the ice age and melting waters cleaned
the loosened stone and earth material out from the gorges and made them clearer. The fractured outlook of
the bedrock is clearly visible in the mosaic like landscape of Saimaa – Pielinen lake. Erosion is active all
the time and different kinds of erosion forms can be seen in the area, e.g. boulder fields and caves
(Kuvaanniemi cave).
Figure 13. Kolvananuuro gorge .
Photos: A. Portaankorva, GTK
Figure 14. . Korkeakoski gorge and rapids.
4. SURFICIAL DEPOSITS IN THE NEED-PROJECT REGION
Finland is the daughter of the ice age. During the last 2,5 million years, several glaciations have shaped
today’s landscape.
Eastern Finland’s quaternary deposits were deposited during the late- Weichselian glaciation. The
Scandinavian ice sheet reached its maximum size about 20 000 years ago (Lunkka 2007), then as a result
of global warming, the glacier began to melt, and its edge reached the southern coast of Finland about 13
100 years ago (Donner 1995). (Fig. 15)
During the melting phase, the continental ice sheet was divided into ice lobes which in turn again
diminished into smaller, independently operating sub lobes. During the last glaciation there were two ice
lobes, Lake-Finland and the North Karelian lobes. The situation of these ice lobes can easily be seen in the
form of the Salpausselkä end formations. (Punkari 1978).
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According to striations and the direction of the elongated landforms e.g. drumlins, the continental ice
flowed from northwest to southeast, but during the melting phase directions of theflow vary. In the eastern
and northern parts of the area the flow was directed from northwest to the southeast while in the
southwest parts, from west-northwest to east-northeast (Map 6).
Figure 15. Distribution of the Weichselian glaciation front margins and the ages of the ice front retreat.
T. Tervo, GTK
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Map 6. Directions of the continental ice flow in Finland.
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QUATERNARY DEPOSITS OF FINLAND
NEED-region
17
JUUKA
RANTASALMI
LEIVONMÄKI
Map 7. The Quaternary deposits of the NEED-project region
KOLI
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4.1. Glacial deposits
The area’s most common glacial deposit type is till, which is unsorted drift loosened from the bedrock and
transported by the continental ice sheet. The grain size of till varies from clay to boulders and it covers the
bedrock in variable thicknesses. Till is deposited in different kinds of landforms such ass drumlins and
hummocky moraines (Map 7).
4.1.1. Basal till
Basal till was deposited under the glacier. It is well graded and compact. Orientation of the elongated
stones in basal till is parallel to the movement of the glacier. Basal till is the predominant sediment type in
the area, and often act s as substratum for other sediments.
In areas where the continental ice sheet flowed rapidly, it has formed basal till streamlined formations,
drumlins. They are elongated ridges parallel with the direction of the continental ice flow. Drumlins were
deposited under the glaciers, often to the distal side of a bedrock obstacle and they usually occur as large
drumlin fields. (Fig 16-18).
Figure 16. Origin of the drumlins. Harri Kutvonen,GTK
Figure 17. Drumlin field .
Figure 18. Drumlin ridge. A. Portaankorva,GTK
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Drumlin fields are situated in the eastern and western part of the area.
The most significant drumlin field of the area is that of Pieksämäki parts of which reach to the western
part of the area under study. Drumlins have been deposited at the birth of Salpausselkäs and their fan-like
orientation reflects the direction of the advancing of Lake Finland ice lobe. (Glückert 1973, Mäkinen
ym.2007)
End moraines were deposited at the margin of the continental ice. They indicate the ancient front of the
ice sheet. Small end moraines , called De Geer moraines, occur in swarms indicating the position of the
front of a step-wise retreating ice sheet. Small end moraines occur in the NE corner of the area. Large end
moraines occur in the zone of Salpausselkä II. The Koitere and Pielisjärvi end moraines in the NE part of
the area are the biggest example of these (Map 7).
4.1.2. Ablation moraine – hummocky moraine
Ablation moraine is made of loose till which is coarser than basal till, often containing abundant sorted
material which is strewn with cobbles and boulders. Ablation till occurs as a thin blanket on basal till.
When in thick layers of independent forms it is called hummocky moraine (Fig. 19-22). These occur in
large fields of usually non oriented ridges or hills and the most significant hummocky moraine fields are
situated in the eastern part of the area.
Figure 19. Deposition of hummocky moraine.
J. Nenonen, GTK
Figure 20. Cross section of hummocky moraines.
Harri Kutvonen, GTK.
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Figure 21-22. Smooth shaped hummocky moraines. A. Portaankorva, GTK.
4.2. Glaciofluvial deposits
Glaciofluvial deposits are formations deposited by meltwaters either under, in, on, or at the front of
melting continental ice. The origin of the material in them is from the glacier itself or from beneath it.
Meltwaters have washed and rounded the grains and sorted them into layers of different grain size.
4.2.2. Eskers
Eskers were deposited at the melting stage of the glacier. They were deposited in crevasses and tunnels in
the continental ice sheet. Eskers are seen on the map as long chains (Fig. 23). The orientation of the
eskers indicates the direction in which the meltwater ran. In this area the most common direction of eskers
is from northwest to southeast. The orientation is perpendicular to the orientation of marginal formations
e.g. Salpausselkä I, II.
Eskers are usually steeply sloping, continuous, smoothly winding ridges (Fig. 24). They most often consist
of sandy and gravelly material although cobble and boulder material may occur the in deep core. Eskers
form a big ground water reserve in Finland.
Figure 23. Origin of esker and kettle holes. Harri Kutvonen, GTK.
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In the region under study, eskers are found in the eastern part of Salpausselkä and in the North Karelian
marginal formations. The sandy formations connected to Salpausselkä ice marginal formations are deltas,
which were deposited in deep water in front of the melting water tunnels. Some of them have continued
sedimentation above the surface in the form of sandurs – dry land deltas. (Donner 1995)
Figure 24 . Metelinharju esker. A. Portaankorva, GTK.
The early phases of the Baltic Sea eroded the slopes of the eskers and ice marginal formations and re
deposited the material in to littoral deposits of varying raised beaches.
4.2.3. Ice-marginal formations
Ice-marginal formations are complex combinations of deltas and end moraines in which sorted sediments
dominate but till is also common.
Due to the occasionally colder climate, the retreating of the continental ice stopped during the Younger
Dryas stage about 12 250 -11 590 years ago. At that time the large Salpausselkä I, II ice marginal
formations were deposited in the front of Lake Finland ice lobe (Fig. 25, 26) (Saarnisto & Saarinen
2001).
Salpausselkä I was deposited about 12 100 – 12 300 years ago. Salpausselkä II was deposited 11 600 –
11 800 years ago 10 -25 km NW from Salpausselkä I.
The North Karelian ice lobe was situated to the north from the Lake Finland ice lobe. Due to the rapid
retreat of the ice lobe, only small and discontinuous ice marginal formations were deposited.
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Figure 25. Kylänniemi, Salpausselkä II, ice marginal formation. A. Portaankorva, GTK.
Figure 26. Origin of ice marginal formation. H. Kutvonen,GTK
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Map 8. Ice marginal formations. H. Kutvonen, GTK.
To the northeast of Salpausselkä, ice marginal formations continue into the Koitere ice marginal formation
which is part of the Rukajärvi formation on the Russian side. To the northwest from the Koitere ice
marginal formation the Pielisjärvi marginal formation is to be found. The most distinguished part of it is
the Jaamankangas ice marginal delta (Map 8).
4.3. Aeolian deposits
Dunes or drifts of aeolian sand are composed of material derived from sorted sediments of glaciofluvial or
littoral origin. Material is fine sand, redeposited by wind and forming single dunes, dune chains or large
dune fields (Fig 27, 28). Fine grained dust transported by wind has been deposited as a thin loess deposit
e.g. in North Karelia. The most significant dune areas are connected with big eskers, interlobate
formations or ice marginal formations.
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Figure 27. Origin of dunes. H. Kutvonen,GTK.
Figure 28. Fossilized dunes. A. Portaankorva, GTK.
4.4. Peat deposits
Peat deposits are formed from the humified remains of mire plants and peatlands often follow the
morphology of the ground surface. The Eastern Finland peatlands are situated near marginal and moraine
formations (Map 7). Deposition of the peat began immediately after the waning of the continental ice. The
oldest peat deposits in the area are situated in the southern parts of North Karelia. (Virtanen ym. 2003)
5. EVOLUTION OF THE LAKES
The lakes in the area were part of the Baltic Sea basin in the early post-glacial period, but were isolated
from it by land uplift (Fig 29, 30). The lakes have acomplex history, having changed in shape, size and
outlet location along with shifts in the rate of uplift from northwest to southeast. (Pajunen 2005)
The evolution of lake Saimaa was very complex. The oldest drainage channels were at the end of the lake
where the most rapid uplift took place. The water level in the lake began to rise and all the independent
lakes in the south were submerged. At the same time a new drainage channel opened up in the southwest.
The shore level that developed before the opening of the Vuoksi channel about 5 700 years ago, is the
highest of the ancient Great Saimaa shores. The river Vuoksi was formed when the waters of Great
Saimaa carved a channel through Salpausselkä I to lake Ladoga (Map 9). Lake Pielinen became isolated
from the Baltic Sea over 9 000 years ago (Fig. 31,32). (Saarnisto 1970, Pajunen 2005).
25
Figure 29. Rates (mm) of land uplift in Finland
Figure 30. Land uplifting phenomena. H. Kutvonen, GTK
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Figure 31. Small river potholes at the bottom of Imatra rapids. A. Portaankorva, GTK.
Figure 32. The early Great Saimaa shore levels are still clearly visible. A. Portaankorva, GTK.
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Evolution of the lakes in eastern Finland (Hannu Pajunen, GTK)
Situation 9500 years ago, formation of the Great Saimaa lake begins.
- vedenpinta kohoaa luoteeseen laskevissa järvissä
- järvet laajenevat ja vesi syvenee
- erilliset järvet yhtyvät ja suurjärvi alkaa muotoutua
Situation 6 500 years ago, maximum extent of the Great Saimaa lake.
- muinaisen Suur-Saimaan maksimivaihe
- järvi laajimmillaan ja syvimmillään
- lasku-uomat Pielavedellä ja Ristiinassa
Present time, The Great Saimaa lake is shrinking and splitting up to smaller lakes
- vedenpinta alenee kaakkoon laskevissa järvissä
- järvet pienenevät ja vesi mataloituu
-muinainen suurjärvi pilkkoutuu erillisiksi altaiksi
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Map 9. Great Saimaa and lake Päijänne in their biggest.
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6. GEOLOGICAL SITES IN NATURE TOURISM
Nature has a lot of magnificent places and sites made by geological processes and all too often we don’t
think about or know the interesting history or stories behind them.
Geological sites provide tourism entrepreneurs new opportunities to diversify their programme selection
and the sites they visit. With combining information about the history or nature/ geology of the area, with
stories and beliefs to the places visited creates interesting and attractive experiences for tourists.
Figure 33. Porosalmen stone cave, Rantasalmi.
Figure 34. Cave and old habitation near Puumala
village. A. Portaanorva, GTK.
The NEED project region includes target areas such as the Koli national park and its national landscape,
Finland's Stone centre in Juuka, the geological paths of Rantasalmi and the national park of Leivonmäki
with its nature routes (Maps 7,10). In themselves, these places are significant, interesting natural and
geological sites. Many other significant geological sites are also situated in the beautiful lake district of
Saimaa-Pielinen, e.g. the Punkaharju esker, the Salpausselkä ice-marginal formations and the Imatra
rapids. Almost none of the sites have been used to meet the needs of the regional nature tourism. They are
still a valuable unused resource for the development of tourism (Map 10).
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JUUKA
KOLI
RANTASALMI
LEIVONMÄKI
Map 10. Geological sites mapped in the region under study (Portaankorva 2009).
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7. LITERATURE
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the Fennoscandian Shield. Geological Suvey of Finland. Bulletin 371, 1-87.
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33-46.
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gradu-tutkielma. Oulun yliopisto. Geotieteiden laitos. 87 s.
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Rainio, H. 1996. Late Weichselian end moraines and deglaciation in Eastern and Central Finland.
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Scientiarum Fennica, Commentationes Physico-Mathematicae, 37. 107 s.
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Baltic ice lake levels. In: Eastern Fennoscandian Younger Dryas end moraines. Geologian
tutkimuskeskus. Opas 32. 7-23
Saarnisto, M. & Salonen, V-P. 1995. Glacial history of Finland. In: Ehlers, J., Kozarski, S., Gibbard, P.
(editos). Glacial deposits in North-East Europe. A.A.Balkema, Rotterdam, 3-10.
Saarnisto, M. & Saarinen, T. 2001. Deglaciation chronology of the Scandinavian Ice Sheet from the
Lake Onega Basin to the Salpausselkä End Moraines. Global and Planetary Change. Volume 31, Issues 14. 387-405
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kallioperä. Geologinen tutkimuslaitos. Espoo. 29 s.
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Eastern Finland. Bulletin of The Geological Society of Finland. Number 59, Part 2.
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O.T. (toim.) 2005. Precambrian geology of Finland. Key to the evolution of the Fennoscandian Shield.
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turvevarat 2000. Geologian tutkimuskeskus. Tutkimusraportti 156. Espoo. 100 s + liitteet.
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