The Đavolja Varoš earth columns (earth features, earth pillars) of unsorted volcanic clastics, high between 2 m and 15 m and wide from 0.5 m to 3 m, topped with large andesite caprocks, are geological forms of indeterminate origin. Each reference to this location of peculiar landforms describes it briefly as erosion of volcanic rocks.
Inadequate scientific argumentation of the evolution of earth pillars in Đavolja Varoš may be due to the overlooking of geological processes that controlled the hoodoo formation.
Earth pillars are erosional features, or forms sculptured by erosion. Their distinctiveness is the product of erosive forces at work, almost invariably the rapid rain-wash of slopes unprotected by vegetation. Which type of rock material is eroding, not the form of erosion is the matter of consideration for understanding the creation of any type of hoodoos, including that of Đavolja Varoš.
A distinctive character of the Đavolja Varoš earth pillars is the rock deposit in which they are curved; rock material is volcanic, and the nature and arrangement of deposit are characteristic of glacial deposits (!). There are not many locations of volcanic rocks shaped into earth pillars: a few in Cappadocia (The Gőreme National Park was added to the UNESCO World Heritage List in 1985)., Central massif in France (Puy-de-Dôme), Valles Kaldera near Santa Fe, Mexico, Crater Lake in Oregon, U.S.A., etc. There are no volcanic rock pillars in Europe comparable to those of Đavolja Varoš. Moreover, Đavolja Varoš hoodoos differ from any other in the derivation of primary deposits curved by erosion. Most columns in volcanic rocks consist of complex layers of friable material covered with harder rocks, like those in Cappadocia. In Đavolja Varoš, however, the deposit consists of volcanic rock debris, in places characterized by inverse grading of coarse fragments like that of moraines. Similar deposits have formed in the areas of calc-alkalic volcanism. Such an area is Lece complex of late Miocene calc-alkalic rocks that include Đavolja Varoš. Many exposures of these deposits, one of which is a cutting of the Kuršumlija-Prolom Banja road, show the primary structure and inverse block gradation.
The volcaniclastic debris flows and even the generation of debris avalanche deposits may result from strong eruptions of acidic to intermediate lava. An explosive volcanic activity may consist of the ejection of abundant pyroclastic material followed by effusion of coherent lava mass. The large mass of volcanic products is unstable and may collapse due to different events or sink to deeper levels. The type of volcanic rock mass movement may vary from the landslide or en masse transport to the mudflow that looks like the torrent from a dam failure or a large flood. In some instances, the debris flows are agents of redeposition; these are relatively slow flows of loose saturated material, sufficiently dense to carry very large blocks of solidified lava. During the flow, fine-grained material 'expels' the coarsest rock fragments that accumulate in the uppermost layer of a deposit.
The described formation of earth pillars is the instance of Đavolja Varoš. Its hoodoo columns consist of unresisting volcaniclastic material dominantly of volcanic dust, sand and small pumice fragments, and subordinately of coarse cm- to dm-size coherent volcanic rock. Largest blocks (even more than half-metre in diameter), accumulated in the upper part of primary deposit, are at present the caprocks that have protected volcaniclastic material from erosion. Erosion probably evolved in the absence of vegetation, but no erosive process could have created the hoodoos without the debris flow deposit in inverse grading of coarse fragments formed through previous evolution of the Lece volcanic rock complex.