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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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Blue Pond
Clay County, Florida

Introduction | Subsurface Characterization

Subsurface Characterization

Blue Pond
Blue Pond. Black lines show profile locations.
Blue Pond appears to be a single large depression, (see B-B' and C-C' below). Many lakes surveyed in this area all appear to have this characteristic (i.e. single basin, single sink), whereas others occur as a complex of depressions. The steep sides of these lakes infer they are young and in the active subsidence or collapse phase (Kindinger and others, 1998). At depth, a strong subsurface reflective horizon at about 30 m below lake level (C-C') is interpreted to be the karst surface. However, interpretations of gamma log profiles to the south (see Section A Index Map and gamma log profile A-A') put the top of the Ocala Limestone at nearly 60 meters below the lake surface.

Johnson (1986) a report that the top of the Marks Head Formation at this depth in a well approximately 4.8 km (3 miles) north of the lake. The Marks Head Formation is part of the Hawthorn Group and is characterized as interbedded dolomite, sand and clay. This horizon is collapsed throughout most of the lake as shown in yellow in the bathymetry map below.

Profile B-B'
Profile B-B'

Profile C-C'
Profile C-C'

The subsurface collapse has created general surface subsidence, as well as slumping of the overburden into the depression (B-B'). Smaller areas of surface collapse are evident at the lake bottom (green line, C-C'). The smaller collapse structures may be a result of accommodation during subsidence, or solution features created by water movement. These surface breaches probably provide pathways for aquifer recharge from the surface waters. The areas of surface collapse have been mapped in red in the contour plot (A-A') below. The bathymetric profile to the bottom of the contour plot (A-A') shows the relationship between the lake bottom, the surface features and the subsurface collapse. Most of the profiles from the survey are obscured by acoustic noise, which masks returns from structure within the depression. The noise and multiples appear to be related to the shape of the seismic lake which produces ringing in the acoustic return. This signature is relatively common (Type 1) and can be compared with similar seismic returns seen in other lakes in the study area.

Depth to lake bottom.
Above: Depth to Lake Bottom

Bathymetric Profile
Above: Bathymetric Profile A-A'

Coastal & Marine Geology Program > Center for Coastal & Regional Marine Studies > Geologic Characterization of Lakes and Rivers of Northeast Florida > OFR 00-180 U. S. Department of the Interior | U.S. Geological Survey
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Updated May 06, 2013 @ 09:24 AM (JSS)