The influence of natural factors, heavy downpours, mudflows, severe drought, and the impact of human activity form sinkholes – massive ground failures.
Most often, sinkholes formation happens in the place of old mines, gutters, and other underground utilities. But natural failures occur due to extreme rainfall, downpours, and mudflows. Rains disturb the level of groundwater over time, moisture washes away the loose ground, covering the already “washed” holes in the limestone. Almost always, natural sinkholes are formed on the limestone layer. It is well dissolved by acidic groundwaters that make millions of holes in the limestone column, and after a long time, some holes become big or small karst caves. Underwater rivers flow in some of them.
Soils or sand covering the limestone layer, perfectly masking the small holes in the limestone layer. And at one point, a large karst failure is formed in a place where there are no visible causes.
Most often, ground failures occur in warm and humid climates, where the process of dissolution and leaching of non-solid rocks by underground and surface waters is most rapid.
However, sometimes karst is also observed in deserts, where such phenomena are most likely inherited from prehistoric humid climate, which became dry long ago.
Karst failures occur regularly and everywhere. But the most famous sinkholes are located in Russian Solikamsk and American Florida.
All karst relief forms are divided into the surface, transitional, and underground.
If karst rocks go directly to the earth’s surface, it is open or bare karst. If they are blocked from above by non-karst deposits, it is covered karst.
Bare karst is found in mountain areas and covered karst in the plains. There is also closed karst, which is noted in areas where karst rocks have great power, and they contain a lot of different impurities.
After the soluble part of these rocks is completely leached, a crust of weathering is formed and it is called terra-rossa (red soil). Further development of karst under this bark goes the usual way. This karst called closed.
The danger of sinkhole is that this widespread hidden process, which prevented the construction and operation of buildings and engineering structures, as well as the rational use of agricultural land. Sinkholes cause significant damage to the population and economy. The main types of the danger of sinkholes include precipitation and earth surface failures; deformation of structures up to their destruction; loss of water from reservoirs through water-soluble rocks; karst water breakthroughs into mountain workings and tunnels; pollution of underground waters;
A vertical failure, pit, cave, or natural well filled with water and located below sea level are officially called blue holes. They belong to sinkholes. These are cavities in the soil, which appear due to the removal of leached and dissolved rock through underground channels. It may also occur through the collapse of the earth cavity vault or by washing out or subsidence of cover sediments.
But after the global cataclysms and the onset or end of the next ice age, the water level in the World Ocean rises, and this funnel inevitably floods – so in the middle of the reservoir, a hole that is noticeably different in color appears. Usually, they are contrasting blue compared to the lighter spectrum of the rest of the water mass, but there are exceptions, such as the black hole Andros. Also, sometimes blue holes are formed not in the sea or ocean, but on land.
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