The Dubí hora NNM covers a small, abandoned quarry at the foot of the north-eastern slope of Dubí hora Hill (463m) above the former monastery complex in Konojedy in the Ústecký kraj (Ústí nad Labem Region). The national nature monument was declared in 1966 on an area of 0.09ha to protect an unusual geological formation – the exposed head of a lava flow with loaf-like jointing.
Well developed columns of analcitite tephrite can be found in the wall of the abandoned quarry. The individual columns have a diameter of around 70cm and are 6-8 metres in height. The most interesting feature is the structure of the individual columns – they are all horizontally broken up at more or less regular intervals so that each one is divided into a number of individual loaf-shaped blocks. All of the edges have been rounded by weathering so that the columns look like loaves of bread stacked on top of each other. This structure is emphasized by the continued weathering, which causes the “loaves” to become more rounded as the surface layers of the rocks peel off. The weathering process has progressed at different speeds on different parts of the wall and some of the loaves have become fully detached from their columns. This is a unique feature among the Czech neovulcanites and this unusual feature is further emphasized on some of the groups of columns as they curve outwards and become narrower in their upper sections, which is probably the result of cooling of the surface of the molten lava and the concurrent movement of the fluid matter inside the flow.
The elongated and forested Dubí hora massif is the remnant of several lava flows, the cooling is the remnant of several lava flows, the cooling of which formed rocks with excellent mechanical qualities. A quarry is in operation near the summit of the hill, where blocks of nephelinic tephrite are extracted. This rock is then split or cut into paving slabs.
The flora in the monument itself is of little significance but several specially protected plant species grow in the buffer zone, including the burnt-tip orchid (Orchis ustulata) and the rock cinquefoil (Potentilla rupestris).
The fauna has not been fully researched but vital populations of sand lizards (Lacerta agilis) and slowworms (Anguis fragilis) live on the floor of the quarrry.
The locality is predominantly used for educational purposes. Professional excursions visit the site to see this interesting natural phenomenon and important vulcanological locality, where the processes of cooling of the magna (curving of the tephrite columns) and weathering of the rock (jointing of the tephrite) can be observed. The operation of the quarry does not influence the subject of the protection. Opportunist trees and bushes are regularly cleared from the quarry wall and its surroundings and fallen rocks are removed from the foot of the quarry wall.