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Natural monuments Moravian

Natural Monument of Erratic Bloc in Poruba

Basic information

Erratic blocs represent boulders of various size made of exotic rocks which do not occur in our lands. They were transported to our lands by the activity of continental glacier during Middle Pleistocene some 250–800 thousand years ago. Erratic block in Poruba was declared a natural monument in 1990.

Subject of protection

The second largest erratic bloc with absolutely the longest axis in the Czech Republic. It was lifted off the creek bed in Poruba in a place called “V dolech” in 1928.


The erratic bloc in Poruba consists of granitic rock described as coarse-grained porphyritic granite. The colour of the rock is pink with black spots of dark minerals. Its structure is porphyritic with 1–2 cm long phenocrysts of pink potassium feldspars. Plagioclase, grey, yellow crushed silica and black biotite in oblong clusters can be found in the coarse-grained rock. It also contains magnetite, apatite, sphene and seldom epidote. The erratic bloc in Poruba, which was dragged here by the glacier most likely from the middle parts of Sweden, is about 320×170×120 cm in size and its weight is about 10.8t.

Porubský bludný balvan 1

Porubský bludný balvan 1

Porubský bludný balvan 2

Porubský bludný balvan 2

Porubský bludný balvan 3

Porubský bludný balvan 3

Useful information


Krajský úřad Moravskoslezského kraje, odbor životního prostředí a zemědělství 28. října 117, 702 18 Ostrava www.kr-moravskoslezsky.cz tel.: +420 595 622 297

GPS position

N 49° 49.359', E 18° 9.191'



Krajský úřad Moravskoslezského kraje
Odbor životního prostředí a zemědělství
28. října 117, Ostrava
Tel.:+420 595 622 297