SINKHOLE FORMATION Lake Jackson Florida, US Katie Reynolds and Anjuli Jackson

Karst Topography H2O + CO2 → H2CO3 Formed in limestone, dolomite Shaped by dissolution of layers of soluble carbonate bed rock Mildly acidic water: H2O + CO2 → H2CO3 Soaks up water like a sponge Little remaining surface water Characterised by: Sinkholes Caves Underground drainage systems 20% of Earth’s dry land surface is Karst

Karst scenery, China

SINKHOLES in Florida Almost 75% of continental US has the right geology for sinkholes Floridian Geology Limestone Sinkholes Three general forms occur in Florida Collapse Solution Subsidence LAKE JACKSON Lake Jackson

Lake Formation Dissolution of uppermost soluble rock Fresh water percolates through fractures Drain water and rain water focussed in depression Debris plugs outflow to form lake Stage 3 Stage 1 Stage 2

LAKE JACKSON Two active sinkholes in the bottom of the lake are remnant features of these karst processes – Lime Sink in the northern portion Porter Hole Sink in the southern area.

LAKE JACKSON The lake is in a closed 27,000-acre drainage basin. Water flows into the lake constantly Water can only leave through evaporation or leakage through sinkholes in the bottom of the lake. Sinkholes open and drain portions of the lake approx. every 25 years since 1800s Low Water Table Low Rainfall/Drought Conditions September 1999 Lake Jackson and all its inhabitants drained down 8ft diameter sinkhole within a few short days

Aerial Photo of Lake Jackson Sinkhole, 1999 “It was spectacular” said Jess Van Dyke, a regional biologist for the State of Florida who was on the scene when it happened. He saw “animals trying to scramble out, a whirlpool or gators, birds and bass went down the hole.”

Sediment being scraped off bottom of lake bed by earthmoving equipment Issues Lake drains into Floridian Aquifer, a source of drinking water Pollution contained in stormwater runoff enters lake Interstate-10 Urban/Suburban development sediment fertiliser Oil Gasoline Sediment being scraped off bottom of lake bed by earthmoving equipment Treat runoff before it enters lake 5 stormwater treatment facilities Removal of sediment from bottom of lake during natural drydown More cost effective than hydraulic dredging Solutions

Lake Jackson Since 1999 Lake slowly refilled due to: regular, wet weather patterns Inflow exceeding drainage In 1957 attempts were made to plug the Lime sink with debris with little success Today: Lake managers believe the natural cycle is best