Exercise 2
The table below describes six types of sinkholes (Waltham et al., 2005). All occur in karst aquifers. Review the table and decide which types of sinkholes would:
- allow direct recharge from sinks to the saturated zone of the karst aquifers?
- allow more rapid movement of water to the saturated zone?
- slow movement or prevent movement of water into the saturated zone?
Types of sinkholes in karst aquifers (Waltham et al., 2005).
Formation process | Host rock type | Formation speed | Typical maximum size | Engineering hazard | Other names in use | |
Solution sinkhole | Dissolutional lowering of surface | Limestone, dolomite, gypsum, salt | Stable landforms evolving over >20,000 years | Up to 1,000 m across and 100 m deep | Fissure and cave drains must exist beneath floor | Dissolution, cockpit, doline |
Collapse sinkhole | Rock roof failure into underlying cave | Limestone, dolomite, gypsum, basalt | Extremely rare, rapid failure events, into old cave | Up to 300 m across and 100 m deep | Unstable breakdown floor; failure of loaded cave roof | Cave collapse, cenote |
Caprock sinkhole | Failure of insoluble rock into cave in soluble rock below | Any rock overlying limestone, dolomite, gypsum | Rare failure events, evolve over >10,000 years | Up to 300 m across and 100 m deep | Unstable breakdown floor | Subjacent collapse, interstratal karst |
Dropout sinkhole | Soil collapse into soil void formed over bedrock fissure | Cohesive soil overlying limestone, dolomite, gypsum | In minutes, into soil void evolved over months or years | Up to 50 m across and 10 m deep | The main threat of instant failure in soil-covered karst | Subsidence, cover collapse, alluvial |
Suffosion sinkhole | Down-washing of soil into fissures in bedrock | Non-cohesive soil over limestone, dolomite, gypsum | Subsiding over months or years | Up to 50 m across and 10 m deep | Slow destructive subsidence over years | Subsidence, cover subsidence, alluvial |
Buried Sinkhole | Sinkhole in rock, soil-filled after environmental change | Rockhead depression in limestone, dolomite, gypsum | Stable features of geology, evolved over >10,000 years | Up to 300 m across and 100 m deep | Local subsidence on soft fill surrounded by stable rock | Filled, compaction, paleo |