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Coastal & Marine Geology Program > Center for Coastal & Regional Marine Studies > Geologic Characterization of Lakes and Rivers of Northeast Florida > OFR 00-180

Subsurface Characterization of Selected Water Bodies in the St Johns River Water Management District, Northeast Florida

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Introduction
Methods
Regional Geology
Karst Development & Characterization
Sinkhole Lake Evolution & Effect of Urbanization
Identification of Karst Features from Seismic Patterns
Summary
Acknowledgements
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Lake Trout and Lake Pike
Lake County, Florida

Introduction | Subsurface Characterization

Subsurface Characterization

Lakes Trout and Pike
Lake Trout and Lake Pike. Black likes show profile locations.
Seismic profiles from Trout Lake and Pike Lake show a hard bottom reflection, possibly well sorted sands, infilling a deeper karst surface (type 1, A-A', below). The strong bottom reflection leads to multiples seen throughout the data that obscure some of the record. The record is also partially obscured in areas where the lake bottom nears the surface. The acoustic characteristics and their interpretation in the two lakes are similar. The subsurface is characterized by numerous small low-angle reflections with high angle reflections dipping toward their center (A-A', B-B', C-C', type 4). Concentric reflections extend to depth in the profile. These features may represent solution pipes or small subsidence into the karst subsurface, which is in close proximity to the surface in this area. This condition has a high potential for increased leakage. A distribution plot of these features (red line) shows how they tend to define the areas of deeper water in the lakes (blue line).

Seismic Proflie A-A'
Profile A-A'

Seismic Proflie B-B'
Profile B-B'

Seismic Proflie C-C'
Profile C-C'

Subsurface features of Lakes Trout and Pike
Trout and Pike Lakes Distribution of Features
(noted from seismic profiles)

The areas of subsidence seen within the lakes are well constrained and do not have the appearance of large subsidence or collapse sinkholes seen in other lakes. These localized areas of subsidence may lie directly over centers of active karst development. The competent overburden restricts lateral growth of the unstable region, confining dissolution, yet creating a direct conduit for fluid migration from the surficial waters to the Floridan aquifer. Discrete reflections at 18 m (B-B', green line) and 24 m (C-C', green line) may represent a karst surface on top of the Ocala Limestone. Interpretations of a gamma log acquired from a well located approximately 1 mile to the south of the lakes (Index Map G, well L-0677) show the top of the Ocala Limestone to be around 50 m (15 ft) NGVD, or about 10 m (30 ft) below lake level. The reflection seen in the profiles (green dashed line) may be associated with this surface. Differential dissolution in the Ocala Limestone could lead to subsequent subsidence in the overlying sediments of the Hawthorn Group and the undifferentiated fill.

Coastal & Marine Geology Program > Center for Coastal & Regional Marine Studies > Geologic Characterization of Lakes and Rivers of Northeast Florida > OFR 00-180

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Updated December 05, 2016 @ 11:25 AM (JSS)