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Glacially sculptured landscapes of Fennoscandia

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Glacially sculptured landscapes of Fennoscandia

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Current and historical trends in Fennoscandian landscapes

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Current and historical trends in Fennoscandian landscapes

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In the history of Fennoscandia, there have been several periods of glaciations and deglaciations/interglacial periods. Weichselian ice sheet covered the area for 15 000 years. As a result of this history of ice ages, Fennoscandia is a classic example of glacially sculptured landscape.

Current Fennoscandian landscapes exhibits drastic variotion in relief and altitudes, featuring both lowlands in southwestern Finland and southern Sweden, as well as mountainous areas on the Norwegian-Swedish border.

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One of the special features of the Fennoscandian landscape is the glaciation-induced erosion. Glacial erosion has resulted in some of the most spectacular landscapes in the region, such as fjords and valleys with U-shaped crossection. Another characteristic of the region are the deep, narrow, longitudinal piedmont lakes, such as the Lake Tornetrask in Sweden. Being situated in soft bed rock, they were easily cleaned and shaped by the glaciers.

In low-lying areas, solid rock surfaces posses lineages parallel to the movement of the ice.

Drumlinoids are drumlin-shaped rocks located parallel to the direction of the glacier´s movement.

Glacier cirques are most often east-facing on the lee side. This is because of deposition of snow by the western wind. Cirques are a product of the early stage of the glaciation

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Drumlins of Fennoscancia. Especially Finland is well-known for its abundant drumlins. Reference: Seppälä 2005.

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The most decisive geomorphic factor in Fennoscandia has been accumulation of soil and rock by glaciers. In Finland, a vast number of drumlins are found inside the Salpausselkä ice-marginal formation.

The last Weichselian glaciation both modified deposits formed by earlier glaciations and deposited new till and glacioflvial sediment layers. Glacially drifted till is the most common deposit in Fennoscandia, covering 95 % of the area in Sweden. After the last glaciation period, a large part of it got hidden under younger deposits.

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Eskers found in Fennoscandia. Notice the Salpausselkä region in southern Finland. Reference: Seppälä 2005

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Proglacial channels were formed parallel to the margin of the ice. They are the predominant trait of the fell region´s landscape, and sometimes they have formed the channel of the present-day rivers.

Running water released from melting ice caps grinded mineral materials into finer particles. Fast-flowing melting waters carried this debri and produced valley trains and sandurs, or outwash plains. On the ice caps themselves, glacier rivers emerged to form a drainage in the weak zones of the ice. Eskers are another type of landscape created by running water released by the melting ice caps. They are especially abundant on the Precambrian Shied area of Fennoscandia. As they were oriented toward the glacial flow, they serve as an indication of the position of the ice divide. Mid-valley eskers often cross the present lakes, which is easily visible on the geomorphological map of Finland. Largest eskers can be hundreds of kilometers long and reach heights of 100 meters.

Crossing eskers in northern Finland are problematic, as some  of these are covered with till, meaning they were deposited by different stages of deglaciation and survived the glacial flow or were formed in meltwater conduits at different levels in the ice sheet.

Basal moraine features are a result of active movement of the ice slobes. Kettle holes, on the other hand, were formed by the  ice sheet lobes imbeded in sediments as it gradually melted. They are a common feature of eskers. Some of them are as deep as 60-70 meters in Southern Finland.

Some of the lakes in Fennoscandia appear in seemingly unlikely places. They were born as lakes dammed by the ice caps. There are several of them on the eastern side of the Caledonian Mountain range. Their shorelines have been eroded by storms and changes in water level of these lakes.

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Baltic ice lake, Yoldia sea, Ancylus lake and Litorina sea depicted in a graph. Reference: Seppälä 2005

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At its peak, the glacier covered the area of the Baltic sea completely. At the end of the last age, the melting waters released by the glacier accumulated into a pool deeper than the rest of the area. The water couldn´t escape into Atlantic ocean because of the land bridge between Denmark and Sweden. As the ice caps still harboured a great deal of water, the oceanic water surface was some 100 meters lower than today. As a result, the Baltic ice lake, an initial phase of the Baltic sea, was formed.

As the melting of the glacier preceeded, the ice lake made contact with the ocean through central Sweden, receiving saline water for the first time. In addition, the water surface rose. This phase is known as Yoldia sea.

The connection with Atlantic ocean was fairly short-lived, being closed by landrise caused by the gradual straightening of the terrain earlier battered by the glacier.  Once again, the Baltic sea became a lake, the Ancylus-lake (named after a genus of fresh-water snails common in the region at the time).

The Baltic sea was yet again connected with the ocean as the glaciers melted in Eurasia and North America. Rising sea level created a new passage for the sealine water to enter the Baltic basin. The Litorina sea was formed around 8500 years ago.

Over time, the percentage of salt in the water has reduced due to reduction of salt water currents through the Danish straits and increasing rainfall. Today, the Baltic sea is a brackish water basin with a salt level ranging from 10 ppt in the south and 1-3 ppt (parts per thousand) in the north.

The different stages of the Baltic sea have had a considerable effect on the spreading of several aquatic species, such as seals (Phocidae) and whales (Cetacea). There is evidence of sea-like circumstances in a Baltic sea in the subfossil-record: the bones of marine species, such as tuna (Thynnus thynnus), the orca (Orcinus orca) and the extinct great auk (Alca impennis), have been found in Gotland. In the fish stock, the changes from lake to sea and to lake again have affected the community greatly. For instance, during the Ancylus-phase, the whitefishes (Coregonus sp.) and cyprinids were probably common, but their populations suffered a major reduction in size as the salt percentage of the water rose. During the Litorina-phase, marine species like the Atlantic cod (Gadus morrhua) and flounders (such as Platichtys flesus) became more abundant, along with the previously mentioned charismatic megafauna.

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Samples of a few avian and fish species inhabiting the current Baltic sea exhibited in LUOMUS. Reference: Kasperi Keränen

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Some species, such as flounders (bottom right) have been more common in the Baltic sea during the sea phases, whereas others, like cyprinids, have faired better during the lake phases. These changes in the fish stock and the changes in the water chemistry behind them have certainly effected both invertebrate prey of the fishes themseves and other vertebrate species preying on the fishes, such as razorbills and cormorants (up left)

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Seppälä (2005). Physical Geography of Fennoscandia. Oxford University Press.
Ukkonen,P., Mannermaa, K.(2017). Jääkauden jälkeläiset-Suomen nisäkkäiden ja lintujen varhainen historia. Museoviraston julkaisuja 8. Museovirasto, Helsinki

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This rather small kettle hole in Seurasaari is one of noteworthy geological sites in Helsinki. Reference: Kasperi Keränen