SINKHOLE FORMATION

Lake JacksonFlorida, US

Katie Reynolds and Anjuli Jackson

Karst TopographyKarst Topography 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

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, ChinaKarst scenery, China

SINKHOLES in FloridaSINKHOLES 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

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 FormationLake Formation

Stage 1 Stage 2

Stage 3

Dissolution of uppermost soluble rock

Fresh water percolates through fractures

Drain water and rain water focussed in depression

Debris plugs outflow to form lake

Dissolution of uppermost soluble rock

Fresh water percolates through fractures

Drain water and rain water focussed in depression

Debris plugs outflow to form lake

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.

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 JACKSONLAKE JACKSON

LAKE JACKSONLAKE 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

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

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.”

IssuesIssues

Sediment being scraped off bottom of lake bed by earthmoving equipment

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

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

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

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 JacksonLake 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

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