They owe their formation to tectonic movements, subsidences of the surface.
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Frequent pools of water lie between the collieries, indicating subsidences of the earth caused by mining.
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The hill is very fragile in places due to springs, underground streams, ancient tunnels and aqueducts, which have caused several subsidences in the past.
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Soil removal from the area to be surface-mined alters or destroys many natural soil characteristics, and reduces its biodiversity and productivity for agriculture. Soil structure may be disturbed by pulverization or aggregate breakdown. Mine collapses (or mine subsidences) have the potential to produce major effects above ground, which are especially devastating in developed areas. German underground coal- mining (especially in North Rhine-Westphalia) has damaged thousands of houses, and the coal-mining industries have set aside large sums in funding for future subsidence damages as part of their insurance and state-subsidy schemes.
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Somewhat weaker but more common are high-pressure areas caused by atmospheric subsidence, that is, areas where large masses of cooler, drier air descend from an elevation of 8 to 15 km after the lower temperatures have precipitated out the water vapor. Many of the features of Highs may be understood in context of middle- or meso-scale and relatively enduring dynamics of a planet's atmospheric circulation. For example, massive atmospheric subsidences occur as part of the descending branches of Ferrel cells and Hadley cells. Hadley cells help form the subtropical ridge, steer tropical waves and tropical cyclones across the ocean and is strongest during the summer.
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Lamač Gate is located in the north- western part of Bratislava to the east of the Devín Gate. Both gates are predisposed tectonic erosion subsidences where parts of the city of Bratislava are located. Lamač Gate forms the continuation of the Záhorie Lowland but it does not connect all the way to the Danubian Lowland. It consists of the mouth of the gate close to the Záhorie Lowland, central part (called the Lamač- Dúbravka part) is the largest and highest part of the gate, it then significantly narrows down between the massifs of Kamzík and Staré Grunty until it finally widens again in the area of the Red Bridge valley at Patrónka.
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Because the deposits thin towards the north, and there are few signs of volcanic necks within the Ochil Hills themselves, it is thought that the eruptive centres were south of the fault, however these are buried deep beneath the Carboniferous rocks including coal measures which are found beneath the low-lying carse lands to the south. To put this in perspective, the prominent hill Dumyat which defines the western extremity of the Ochil Hills has a height of 418 metres. The nearest colliery, Manor Powis, approximately 2 km south of the fault, was approximately the same depth, in carse land that is scarcely above sea level, and was mining coal from Carboniferous strata at least many hundreds of metres above the top of the Devonian deposits. The Ochil Fault was active from the earliest part of the Carboniferous period, allowing the marine swamps in which the coal-producing vegetation flourished to be periodically overlain by layers of sand, forming sandstone, or silt, forming shale, in a number of cyclic subsidences.
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After a further, short stretch southward, the wall suddenly turns right, always flanking the street, that now changes its name into Viale delle Mura Gianicolensi. At the corner there is a quite battered plate, in memory of the works of restoration: “PIUS IX PONTIFEX MAXIMUS PROPUGNACULUM INNOCENTIO X P M EXTRUCTUM ANGULIS PRORUENTIS LABE[…] FATISCENS NOVA MOLITIONE A FUNDAMENTIS RESTITUTUS IUSSIT ANNO MDCCCLXI IOSEPHO FERRARI PREF. AER.” Next to the plate, a plaque “S.P.Q.R. MDCCCXLIX” remembers the events of 1849. Furthermore, the entire stretch of wall from here up to Porta San Pancrazio is a sequence of signs, more or less visible, of restorations (patchings, traces of subsidences and collapses), that evidently lasted at least until 1861, according to the just mentioned plate of Pope Pius IX. All along this first stretch, up to the crossing with Via Fratelli Bonnet, the inner side of the wall encircles the area of Villa Sciarra and is only partially visible since, in some places, it is covered by an embankment giving a modern example of the ancient agger, probably similar to the one next to the Servian Wall.
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