Jeziorna (285 m), located in the northern part of the Kaczawskie Foothills near Nowy Kościół on the left bank of the Kaczawa Valley, stands out among the basalt elevations in the region due to the presence of a water-filled former quarry in its central part. Like many other hills, it is an example of an eroded volcanic cone, mainly composed of solidified lava from a former volcanic vent.
In the peripheral parts of the former quarry, volcanic pyroclastic deposits – breccias and volcanic tuffs – are exposed. The quarry has approximate dimensions of 100 × 100 m and wall heights of up to 30 m. The basalt exposures on its walls reveal columnar jointing, formed during the cooling of lava and the associated reduction in volume. In the walls rising above the water surface, the columns are visible in cross-section, suggesting that the axial part of the former volcanic vent, with a column arrangement resembling a vertical one, was located in the central part of the quarry. Probably due to the presence of a water reservoir in the lowest part of the former quarry, which has a fairly regular, circular outline, this feature is sometimes referred to in some popular and tourist publications as a caldera (a form created by the collapse of a volcanic cone into an emptied magma chamber), which is completely erroneous. The approach to the quarry is unmarked, and steps that have been preserved allow descent to the lake’s shore.
Description: Piotr Migoń
