Geology

To the west of Vuus, Salpauselkä runs through the whole of Southern Finland and dives into the waves of the Baltic Sea at the tip of Hankoniemi. The marginal formation corresponding to the Salpausselkä continues in a discontinuous and less developed form into Sweden, northern Norway and further into Russia, from where it curves through North Karelia back to the edge of Vuoksi, this time on the east bank of the river. Although there are large gaps in the ring, the chain of formations consisting of sorted soil types and moraine encloses the whole of Fennoscandia and shows exactly the extent of the ancient continental glacier more than 12 years ago. Vuoksi pierces a small but important gap in the ring in terms of Eastern Finland. 000 years ago, it broke its way into the lowest point of the sand-dominated part of the edge formation and since then has regulated the development of the lake landscape of Saimaa and the whole of Eastern Finland, paced by the slow uplift and tilting of the land. Vuoksi has also influenced the development of the natural landscape of Karjalankannas and Laatoka.

Imatra is therefore located at the intersection of major geological formations. People have lived in the ever-changing water labyrinth of the Salpausselkä dam and Saimaa flowing through Vuoksi for thousands of years. Vuoksi's stem has been moved up and down. They have been traded, spread to the fishy lakes and left an innumerable number of settlements and most of Finland's famous rock paintings at the foot of the ancient shores.

Stone Age people functioned in the geological environment, perhaps unknowingly adapting to its changes, just like us. The sites of Imatra's georoute tell about the history of local nature and the inanimate framework of living in a time perspective that may require some getting used to from those living in a quarter economy.

Imatra bedrock

The foundation of the Vuoksi riverside landscape, the ancient bedrock with its stone species and the structures visible in them, is a window into the landscape's past. The main rock types in the area are mica gneiss and various granite rocks. Both of them have their own birth history.

A mountain rose from the sea

The formation of the mica gneisses of Imatra and their related rock species began at the bottom of the ancient sea more than 1 million years ago. Clay, calcareous silt and carbon-rich mud were transported from the continental area, which gradually settled on the sea floor in thick layers. Sand was deposited on the shores of the islands and in the estuaries. There are also indications of volcanic activity in the area of ​​present-day Salo-Issaka.

The layering phase was followed by a seismically active phase, during which a collision zone of the slabs of the stone circle developed in the area. The ancient sea closed, and a mountain range rose at the point of impact about 1885 million years ago. The large broken zones of the southern Saimaa bedrock, which can be seen in the current landscape in the direction of the lake basins and also in the course of the old rapids bed of Imatra, probably originate from those times.

During mountain folding, marine sediments were pushed into the roots of the mountains rising into the collision seam. Internal heat and high pressure caused the rock masses to recrystallize. The minerals of the rock species reveal that the mica gneiss formed from ancient marine deposits had a transformation temperature of about 650–700 degrees and a pressure of about four kilobars. There used to be about 15 kilometers of stone on top of the current rock surface.

The rock melt crystallized into granite

Vuoksenlaakso's granitic rocks are younger than mica gneisses. Hundreds of cubic kilometers of granitic rock melt crystallized deep in the mountain's root parts slowly into coarse-grained granite, so-called pegmatite granite. In addition, rock melt penetrated into the cracks and weak zones of mica gneisses. As a result, common mixed rock types, or migmatites, were formed in the area. The period of wear that followed the folding of the mountain and is still ongoing has revealed the mica gneisses formed deep in the earth's crust and the granitic rocks crystallized from rock melt in the current earth surface section. The hallmarks of mica gneiss rocks are the overall gray tone and the oriented and often striped appearance. Pegmatite granite rocks are reddish in color due to the feldspar they contain, have a coarse-grained structure and are also often speckled with dark red garnet crystals. Garnet is a semi-precious stone. Sufficiently intact crystals are commonly used as raw material for bevelled jewelry.

The bedrock of Imatra was formed near the equator

When it was born, the rock block of the Imatra area was located near the equator at approximately the same latitude as present-day Egypt. If analogies for the birth conditions of stones are sought from the present-day Earth, then geological environments similar to the early stages of development of Vuoksi's bedrock could be found in the sea areas surrounding Japan or in the Indonesian archipelago. In the case of Imatra, only primitive cyanobacteria witnessed the course of events. When the stone species of Imatra were born, they represented the highest level of life development. The stones of Vuoksi got their current appearance under conditions that prevail under the Alps, for example, at a depth of about 15 kilometers.

Imatra under the continental glacier

The solid bedrock is covered in a perforated veil by soil consisting of loose soil types. Imatra's soil has been created during the last 20 years as a result of the erosive and depositional processes caused by the continental glacier and the coastal shifting, river erosion and swamping that followed the melting of the glacier.

The thick mass of ice that once covered Finland and the rest of Fennoscandia slowly flowed towards the edges of the continental glacier. Ice flowed from the accumulation area located in the middle of the continental glacier to the melting area of ​​the marginal zone even when the edge of the continental glacier stayed in the same place or even retreated.

Glacial ice and the rock material transported in its bottom part consumed its rock base. As a result of grinding, ridged silo rocks were created, which are common on the shores of Saimaa. The grooves show exactly the direction of the ice. In the last phase, the ice masses flowed from northwest to southeast on Imatra.

Local melting and refreezing of ice occurred in the steep rock areas at the base of the continental glacier caused by pressure fluctuations. The water frozen in the rock crevices dislodged and Louhi large pieces from the rock elevations. They were carried away by the flowing ice, mixed with the rest of the rock and later deposited as a moraine when the ice melted. The bouldery nature of the surface moraine is especially characteristic of the formations of the northern parts of Imatra.

The continental glacier shaped the landscape

The edge of the melting continental glacier reached the coast of Southern Finland about 13 years ago, and the Imatra area began to be exposed from under the ice. The melt waters flowed in torrents like glacial rivers. They transported and sorted the aggregate and deposited sand and gravel in the tunnel beds, in the grooves of the edge of the ice and on the edge of the glacier. In today's landscape, the deposits are visible as ridge humps (100), the most representative of which is Mellonmäki, known as a viewpoint. When Mellonmäki was born, it was a small island on the edge of the Baltic ice lake. The common De Geer moraines (1) in the Imatra agglomeration are also from the same period, which are therefore about 2–12 years old. They are low moraine ramparts parallel to the ice edge, born next to a glacier that ended in deep water, and often occur in flocks of dozens of ridges. There are also individual large boulders along the stream. Some of them have probably fallen to their current location from the melting icebergs that have flown over. At that time, the water depth was around 800–12 meters in large areas.

An arc was formed at the edge of the continental glacier in the Saimaa area, which stretched from Joensuu via Imatra to Lahti. The arch delimited the part of the glacier known as the Järvi-Suomi flow tongue. Kieleke had managed to retreat about 50 kilometers to the northwest of Imatra, when the climate got colder again. As a result, the ice masses rolled again to the northern parts of Imatra, where the edge of the continental glacier remained for a couple of centuries. At that time, between 12 and 300 years ago, the melting waters deposited an almost continuous chain of estuaries (12) on the edge of the Järvi-Suomi ice shelf, consisting of different types of land, whose flat legal areas rise to a height of more than a hundred meters. It corresponds to the level of the Baltic Ice Lake at that time. When the estuarine deposits were formed, the alternately advancing and alternately receding ice edge pushed moraine wedges between the gravel layers and also pushed a number of large and rocky marginal moraine ramparts in front of it (100). This formation consists of the first Salpauselkä diagonally cutting the northern parts of Imatra.

Saimaa and Vuoksi

Although the continental glacier stopped shaping the landscape of Imatra about 12 years ago, its indirect effect on the development of nature has continued with land uplift until today. The rise of the earth's crust buried under the kilometer-thick mass of ice towards the pre-glacial position and the related tilting of the earth's surface to the southeast have partly regulated the area's coastal shift. This is the single most important phenomenon that has affected the landscape of Imatra since the melting of the ice. Today, the ground rises in Imatra by about 000 millimeters per year.

On the southeast side of Salpauselkä, the shifting of the shoreline is related to the stages of the Baltic Sea, and in the northwest, shoreline movements are part of Saimaa's history. At its lowest point, the level of Saimaa in Imatra has been twenty meters lower than the current level. At that time, it was about eight kilometers from Lammassaari to the nearest beach. The other extreme is represented by the Suur-Saimaa phase before the eruption of Vuoksi about noin 5 700 vuotta years ago. At that time, the surface of the lake was several meters higher than it is today, and Lammassaari was much smaller than it is today. The birth of Vuoksi changed the development direction of Saimaa and started a phase of river erosion in Imatra, the traces of which dominate the landscape in the entire area of ​​the Vuoksi riverbed.