ancient culture in lake saimaa area
According to our best knowledge, the first people arrived to the Saimaa area from east and south east approx. 11,000 years ago. The scenery was quite different in that time: the people settled in dense birch forests that had first arrived to the areas liberated from ice. Pine spread here only little later, followed by noble deciduous trees approx. 8,000 years ago. Spruce is kind of a newcomer in our nature and started to spread here from east, not sooner than at the end of the Stone Age. Not much is known of the early inhabitants but, based on archeological findings, they had tools made of flintstone, same kind as in Kunda culture in ancient Estonia. Apart from few single exceptions, no remnants made from other materials than stone or burnt bone have been preserved in our acidic soil. For the same reason,the ancient dwelling sites are not found easily in the terrain. However, ancient ground depressions have showed that the people lived in timber huts, partly dug in the ground. It is known, based on the development history of Saimaa, that the ancient habitats were chosen the same way as a modern Finn would choose a place for a summer cabin. The habitations were founded on sunny beaches under hills. The best habitats were used for hundreds, perhaps thousands of years.
Article image: Rovastinoja reconstructed Stone Age dwelling, desinger Risto Järvisalo.
SALPAUSSELKÄ ICE-MARGINAL FORMATIONS
In the final stages of the Ice Age about 12,800 years ago a cold climate period took place, known as Younger Dryas. During the cool period the receding of the melting ice sheet slowed down and, at some points, stopped completely. The First and Second Salpausselkä ice-marginal formations, which can be seen even from space, were formed 12,300–12,100 and 11,800–11,600 years ago when the edge of the glacier stayed stagnant. The melting ice transported rock material and deposited it as till, gravel and sand. At Salpausselkä’s, boulder-rich ice-marginal moraine is distinctive at the proximal side, the distal side being characterized by delta-forming sand and gravel. As a remnant from the labour of the glacier, two large-scale banks lie on the Saimaa area, interspersed by here and there meandering regions of eskers and kettle terrains. The great Baltic Ice Lake had formed from the glacial melt waters. The melting process transported the finest material to open waters, which then deposited and formed layers of varved clay.
1. Ground moraine
The flowing ice eroded boulders and smithereens out of the bedrock. When the ice melted away, the rocky material was deposited as dense ground moraine which covers most of the bedrock in Finland, typically as a layer few meters thick.
2. Ice-marginal moraine
Ice-marginal moraine was deposited when the Salpausselkä’s were formed. It typically consists of sandy and rocky till, placed by the glacier at its edge.
3. Sand and gravel
The melt waters of the glacier transported and sorted material the same way as rivers do, forming gentle-sloping sandy deltas at the distal side of the Salpausselkä’s. Eskers consist of gravel and sand, deposited in melt water tunnels inside the glacier. Today, delta and esker territories are important sources of sand and gravel.
4. Varved clay (glacial clay)
The melt waters of the ice sheet transported the finest material far out to the open waters. When it accumulated, deposits of varved clay were formed. The continuous layers (or varves) are connected to seasonal variation: dark thin layers were formed in wintertimes when the melting was slow and pale thicker layers in summertimes when the melting accelerated.
5. Post-glacial clay
Clays which were deposited after the glacier was melted are called post-glacial. They have no layered structure and they contain more organic matter than glacial clay.
Peat is a soil type which consists of incompletely degraded organic material which accumulates in marsh areas. The first peat lands in Finland started to form locally quite soon after the land was set free from ice and the low-lying territories were uncovered from water.
CONTINENTAL ICE SHEET AND IMATRA STATE HOTEL
During the last two million years, cyclic glaciations have dominated especially the northern hemisphere of our planet. The last of them, Veiksel glaciation, begun in Europe when the climate cooled approx. 118,000 years ago and the continental ice sheet started to grow in Scandinavia. The glacier had extended to its maximum, to Middle Europe approx. 25,000 years ago. In that time, the ice covered the whole Finland’s area as two-kilometers thick bed. The maximum thickness of the glacier is expressed in the adjacent pillar on a scale of 1:500. At the feet of the ice pillar, on the same scale, is a model of the Statehotel which is located by Imatrankoski rapids. The Statehotel, originally Grand Hotel Cascade, has been built in 1903 and it is a graceful historical attraction. It represents jugend style, typical for its time and it has been designed by architect Usko Nyström.
THE EROSION FORMS OF THE GLACIER
During the Weichselian last glaciation maximum, the continental ice sheet extended to Middle-Europe approx. 20,000 years ago. For tens of thousands of years, the glacier eroded its base and these erosional marks are still visible in our landscape. The glaciation center was located at the Bothnian Bay, from where the ice slowly flowed towards its margins. Enormous pressure was present at the bottom of the glacier and the flowing ice mass broke and crumbled rock material from the bedrock. It has been estimated that during the last glaciation the ice eroded our bedrock as much as seven meters on average. In many areas the rock load at the bottom polished rocky hills to rôche moutonnées. The glacier grinded the fragile zones of the bedrock to gulleys and erosion valleys. Today, many of these can be seen in the landscape as longitudinal, steep-sloped lakes, showing the direction of the ice flow. Similarly, many zones of especially hard rocks have remained as hills, rising from their surroundings.
DRUMLINS AND FLUTINGS
In the areas of active ice flow, till deposited in the direction of the flow, forming longitudinal moraine ridges called drumlins and flutings. Drumlins are typically few meters tall and droplet-shaped formations that can extend up to few kilometers in length. In many cases, crescent troughs can be found in front of them. Flutings are similar formations but they are linear and smaller in height. These two kinds of moraine ridges are present as fan-like fields in many areas. Different suggestions about the exact mechanism of their formation have been proposed but it has been noticed that they often have a rocky core in their topside head. According to the generally accepted theory, the ridges have formed when the flowing glacier deposited its rocky bed load behind a strong obstacle.
Till is our most common soil type. It is unsorted or poorly sorted soil type, meaning that it contains all grain sizes from clay to big boulders in variating ratios. There is not flowing water action related to the deposition of glacial till formations (or moraines) because till is material mechanically eroded by glacier and after the glacier melted away the material was deposited in situ. Because there has not been eroding action of water the clasts are typically poorly rounded. Many of our terrain shapes are consisted of till, for instance the great ice-marginal moraines of the Salpausselkä’s and the droplet-shaped drumlins following the flow direction of the ice. Most of our bedrock is covered by ground moraine, composed of the material crumbled and deposited beneath the glacier.
During the melting phase of the continental ice sheet, boulders stocked in glacial rivers which flowed inside the ice. In some places the strong currents lasted for centuries, whetting stones to rounded esker boulders. These symphatic rock spheres can be found on esker terrains but also elsewhere, where they have been transported by the ice.
Gravel, like sand, is a well sorted soil type. Esker gravel was deposited in the glacial melt water tunnels by strong currents. It is typical that the core of the eskers in composed of coarser material than the upper parts, even boulders. This kind of structure is a result from the fact that when the eskers started to form the flow velocity was often high and was able to deliver bigger rocks. The strong current eroded the stones and, because of this eroding ability of streaming water, the esker gravel clasts are rounded. While the gravel-sized particles were deposited the finer material still drifted with the current, to be deposited in some place else with calmer flowing conditions.
Grain size: 2–20 mm
Sand is a sorted soil type whose grain size variation is relatively even. Sands are deposited at beaches and river environments because of the streaming and sorting action of water. In the Ice Age, enormous quantities of sand was deposited in melt water ravines and deltas of the glacier. The melt waters on the ice surface caved tunnels through the glacier and strong rapids transported the material the glacier had captured. When the currents calmed near the edge of the glacier, the sandy material was deposited on the riverbed. When the glacier melted down and its edge receded the sand deposits were left behind and can now be seen in the landscape as longitudinal esker formations. In front of the ice sheet, at the river outlet channels, the sand formed delta areas. Sand and gravel formations are our best ground water sources.
Grain size: 0.2–2.0 mm
The melt waters from the glacier transported fine material which did not immediately sink to the bottom but drifted along with the current to the open waters before finally descending down to the bottom of the Baltic Ice Lake. Thus, the clay terrains in Finland have been deep-water stratification environments. The varved clay or glacial clay deposits consist of continuous layers of pale and dark material. The layers resemble the growth rings of trees. The pale layers have formed in summertime when the melting of the ice accelerated, while the more fine-grained layers formed in wintertime when the melting correspondingly slowed down.
Grain size: < 0.002 mm
On the river banks of Mellonlahti and Vallinkoski one can find strange light-coloured pebbles called Imatra stones. They are chalk coagulates, formed in clay deposits of Vuoksi area during the melting phase of the continental ice sheet. When porous fine-grained layers contained enough carbon dioxide and bicarbonate local oversaturation lead to concretion of calcium carbonate. As a result, strange-shaped limestone pebbles were formed. Once Imatra stones were sold as souveniers but nowadays collecting them is forbidden. The stones exhibited in this vitrine are received from the collections of the Imatra Town Museum.
Amadeus rock or garnet-cordierite-gneiss is a multicoloured, mainly greenish, gneissic rock native to Sulkava region. Gneisses are metamorphic rocks which have formed when a pre-existing rock has recrystallized under high pressure and temperature. Amadeus has originally been a part of ancient seabed that has ended up in an mountain folding event about 1,900–1,800 million years ago. During the upheaval of Earth’s crust the rock has partly melted, recrystallized and transformed into banded gneiss. On it, light granitic veins, dark gneissic bands and reddish garnet mineralizations can be seen. Because of its elegant multicoloured texture, amadeus is used in interior decoration and monuments.
Main minerals: feldspar, quartz, biotite, cordierite, garnet
This plagioclase porfyrite is a metamorphic volcanic rock. Volcanites are composed of solidified and crystallized lava, dismantled on ground surface or near it. From Finland’s ancient bedrock, these kinds of surface rocks have eroded away ages ago, despite some fragments which have got wedged deep in the crust as a result of several plate collision events. These fragments of the old crust have gone through metamorphosis in high pressure and temperature. The light thin grains scattered in the fine matrix of this rock are plagioclase mineral.
Carbonate rocks are composed mostly of carbonate minerals, usually calcite or dolomite. They are typically formed on the seabed either by precipitation or when the remains of chalk-shelled organisms accumulate. The carbonate rocks in Finnish old bedrock have gone through metamorphosis several times because of risen pressure and temperature.
Main minerals: calcite, (dolomite)
Calcite or calcium carbonate, found from Ihalainen excavation, Lappeenranta, is bluish marble. Small-scale limestone deposits are scattered all over Finland. They have formed from chalk rich material, stratified in an ancient shallow, warm sea. Since then, the rocks have gone through several stages of metamorphosis and, in some cases, have hardened to beautiful marbles. Calcitic limestone is used for many purposes, for instance as a resource for burned chalk and cement, industry and soil improvement agent.
Main minerals: calcium carbonate
Gabbros are dark plutonic rocks, crystallized from molten magma deep in the Earth’s crust. Their alkaline composition is the same as in basaltic lavas which are dismantled especially at the middle ridges of oceans. Gabbros and other alkaline plutonic rocks are economically valuable because they apply well as a resource for building industry and they offer significant nickel-chrome and copper deposits. Gabbro is also known as ”black granite” but this term is quite misleading as their chemical and mineralogical composition differs from each other.
Main minerals: pyroxene, plagioclase, hornblende, olivine
Granite is an igneous rock, slowly crystallized from magma deep in the Earth’s crust. Due to the slow crystallization the minerals have been able to grow to rather big grains. Granites name comes from Latin word granum, meaning grain. Most of our granites have been formed approx. 1900–1800 million years ago. Granite is one of the most common rocks in our bedrock and it has been declared as our national rock. Granitic rocks naturally contain small quantities of uranium and thorium which are unstable elements and therefore emit radioactive radiation and produce radioactive gas radon. Granite is hard and tough and is well suited as a construction material.
Main minerals: alkali feldspar, plagioclase, quartz, micas
Granodiorite is a granite-like igneous rock. The main difference between these two is the fact that granodiorite contains more plagioclase than alkali feldspar, unlike granite. Granodiorites also tend to be more dark-coloured compared to granites, which is because of the black mineral hornblende.
Main minerals: plagioclase, alkali feldspar, quartz, micas, (hornblende)
Very coarse-grained igneous rocks are called pegmatites. Their grainsize varies but the coarsest-grained ones can contain crystals of several meters in size. Pegmatites typically occur as veins or lenses and their chemical composition corresponds to their surrounding rocks. Granitic pegmatites are the most common ones. Pegmatites often contain gemstones such as beryl and topaz as well as hi-tech metals, which provides economic interest for their exploitation.
Main minerals: feldspar, quartz, micas
Rapakivi is one of the few Finnish words that have been adopted to other languages as they are. The name is derived from word ”rapautua” (= weather) due to the rocks tendency to easily erode. Rapakivi granites are native to all continents and most of them have been formed in Middle-Proterozoic, 1,800–1,000 million years ago. In Finland rapakivi granites occur as wide areas and they are crystallized remnants of the magma chambers of ancient volcanoes. After millions of years of erosion, the rocks have been revealed to the surface. Rapakivi granites (1 650–1540 million years) are some of the youngest rocks of our ancient bedrock. They are relatively easy to identify from their 1–5 cm wide alkali feldspar ovoids which can have light circles of plagioclase around them. Name for that kind of rapakivi is viborgite.
Main minerals: alkali feldspar, plagioclase, quartz, micas
Tirilite is a fayalite bearing, dark-coloured and even-grained variant of rapakivi granite. Its identification by first sight might be challenging due to its unusual dark colour. The name of this rock comes after its find site, the Tirilä village of Lappeenranta.
Main minerals: alkali feldspar, plagioclase, quartz, olivine (fayalite), hornblende
Minerals are crystalline compounds found in nature. Rocks consist of mineral grains and the most common ones are quartz, feldspar and micas. The exact determination can be, however, difficult without laboratory studies. If the mineral grains in the rock are rather large, a preliminary identification can be carried out by studying the physical properties of the minerals. A geohiker who wants to learn mineral identification, can use a steel spike or knife, a magnet, non-glassed porcelain and a magnifying glass.
crystal structure and appearance
Every mineral has its own uniform crystal structure. This structure defines what kind of surface shapes are possible for the grain. The physical conditions during the crystallization define what kind of shapes the mineral can form. Sometimes the physical environment allows the mineral to form perfect crystals, expressing its charasteristic crystal structure. However, these kinds of perfect crystals are relatively rare in nature. Still, minerals can be identified by their appearance, for it can often reveal the crystal structure of the mineral. For example, flat or thin grains are usually micas.
Hardness is often a good single essence. When identifying minerals by their hardness, we can use the Mohs denary scale for hardness, in which 1 = the softest (chalk) and 10 = the hardest (diamond). A mineral upper in the scale grazes the lower ones and minerals with the same hardness graze each other. When defining the hardness, a steel spike or knife (hardness = 5,5) or an iron nail (~5) can prove useful. The tool cannot graze any material harder than itself. Minerals harder than quartz (>7) are usually gemstones.
color and scratch
The color of the mineral can be useful in the identification but generally speaking it is rather weak sign because the same mineral can occur in several colors. Scratch means the color of mineral powder and it is a significant feature especially when identifying ore minerals. The scratch can be made by grazing the mineral against non-glassed porcelain like an old fuse. Ore minerals (oxides and sulphides) give a strong-colored darkish scratch and other minerals typically a pale scratch. Thus, silicates give usually a gray or green scratch, whereas the dark ore mineral’s scratch is black, brown or red.
When considering the most common minerals, only magnetite shows strong magnetism. The magnetism is an important sign when distinguishing magnetite from other ore minerals. Pyrrhotite shows magnetism occasionally. The iron meteorites are often magnetic. Whether the mineral is magnetic or not can be noticed with a magnet.