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Volcanoes

Machovy lomy

A group of abandoned quarries among Chuchelna village, town of Semily and electricity transformation station Na Rovném is named after original owners Machovy lomy. Exactly in this area, 5 million years ago, lava from Kozákov flew into the Paleojizera river valley. There is an unexcavated cone of basaltic rock in the southern quarry near the villa of the owners. A compact basanite forms only the crust of the cone, which is filled with reddish volcanic breccia.

Basaltic jointing

Columnar jointing

Such a volcanic form is called root-less crater.

Root-less crater

Root-less crater

It is product of steam explosion through a lava flow. The steam comes from water-saturated sediments rapidly covered by hot lava flow. Resulting chimney goes through the lava and it is filled with quenched lava clasts. A bigger quarry on the northern side of the plateau has two parts. The bigger part exposes the upper part of the lava including autoclastic breccia on the top. A large quarry scarp exposes fantastic colonnade of columnar-jointed basanite. In fact, there are two colonnades, but these do not reflect two lava flows. Two colonnades form in a single lava body as a result of two cooling fronts – one from the top and the second one from the bottom. A smaller part of this quarry exposes the base of the lava flow. There are sediments of the Paleojizera River preserved beneath the lava. The sediments contain also hyaloclastites derived from quenching of the lava front. High effusive rate covered soon the entire valley and its sediments with lava. Later, river started to cut a new valley slightly to the north.

Excursion at the root-less crater

Excursion at the root-less crater

GPS position

N 50° 38.785', E 15° 18.470'
[GPX]

[MAPY.CZ]

Contact

Geopark UNESCO Český ráj
Jiří Vlasák
e-mail:vlasak@geopark-ceskyraj.cz
http://www.geopark-ceskyraj.cz