crown and sink holes

• Crown holes and sinkholes are becoming more common due to increased rainfall. 
• Crownholes:

  • Crownholes form due to subsurface human activity
  • Heavy rainfall gets into the voids and enlarges them 
  • More of the void dissolves due to water and increases in size 
  • Eventually the roof collapses
• Sinkholes:

  • Form due to natural dissolution of the bed rock 
  • Mainly happens in limestone and chalk but salt and gypsum are also at risk 
• Sinkholes:

  • Acidic water enters joints and enlarge them 
  • Letting more water in
  • Forming underground caves 
  • Rock dissolving causes soil to be dragged down making a funnel shape impression 
  • Depression collects rainwater which infiltrates through the soil and percolates into the rock 
• Sinkholes:

  • Clay presence may cause pond formation 
  • Increase in water due to rainfall increases overlying weight 
  • Drought lowers the water table which doesn’t support the weight of the roof