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What causes sinkholes?

A sinkhole is a hole that opens up suddenly in the ground.  Natural sinkholes occur mostly because of erosion and underground water.  They start developing a long time before the hole appears. Sinkholes can also be man-made. They can happen as a result of drilling, construction, mining or even heavy traffic.  Sometimes a broken pipe can cause a sudden increase in water underground or forms a pool.  This can also cause a sinkhole.  Water can erode the ground underneath the streets and cause sinkholes, as well.  Heavy weight that presses down on soft earth can also cause a sinkhole to develop.  

Sinkholes can be dangerous.  They can be a safety concern for people and dangerous to the foundations of buildings.  They can cause toxic materials to enter and pollute the groundwater.  The biggest problem is that they can appear suddenly with no warning, and they can wind up causing a lot of damage.