State historical-architectural, landscape and natural museum-preserve «Izborsk»

The territory of the North-West of Russian platform, on which the famous town of Izborsk is located, has been forming during the geological history of our planet for million years undergoing different transformations. At the foundation of the platform, at the depth of 550 meters there is a crystalline foundation, laid by granites, gneisses and slates. The formation of the foundation was completed about 1 billion years ago. The surface of the foundation is not even. It is coated with a sedimentary cap, mostly represented by limestones, formed 600-350 million years B. C. (V. K. Lesnenko, 1993). The accumulation of limestones went under the influence of tectonic processes.

Limestone has been the main construction material in Izborsk for a long time (now the exploitation of all the minerals is prohibited). It is limestone that Izborsk people used to build the fortress on Zheravia hill of. The ancient stone impregnable walls have been standing resting on limestone slabs, which Zheravia hill is formed of. These walls have survived many sieges and now impress with their strength and might.

The appearance of Izborsk and its vicinities was formed as a result of the last Valdai glaciation. The Pskov region was completely covered by the glacier. Advancing, the glacier was covering every living thing, ploughing up the ground, leaving great grooves, changing courses of the rivers. The glacier left the territory of Izborsk 10-12 thousand years ago, having left vivid traces of its former presence. The glacier brought huge granite boulders, sand and when it melted, it covered the layer of limestone with them. Huge boulders can still be seen, covered with moss and lichen.

When the ice was melting the valley which was formed became a reservoir for the water from melted ice. This is why Izborsk valley is not a river valley and has a special trough-like shape. Nowadays except the glacier time forms of relief there have survived pre-glacier forms of relief as well.

There are many ravines and depressions in Izborsk vicinities. Their origin is connected with karstic processes, which are so typical of the area.

The presence of deeply bedded carbonate rocks, the great amount of rainfall and underground springs provide conditions for karst processes. These processes have formed such forms of relief which are represented by craters of various forms: conic, bowl shaped sinkholes, «blind» karst ravines and other forms.

Karstic processes have also influenced the formation of a great number of underground springs, closely connected with surface water.

All the above mentioned factors contributed to the formation of bright and mosaic relief.