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Lowry & Magnolia Lakes

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Location of seismic profiles collected from Lowery and Magnolia Lakes. Click on the numbers in red to view Figures 28, 29, and 32.
Figure 28 Figure 29 Figure 32 Lowry Lake, also located in Clay county (approximate latitude 29° 50"42"N and a longitude 81° 0' 14"), is a semicircular lake about 2 by 3 km (
Fig. 3). This lake, unlike Kingsley, has buried and implied active subsidence features (Figs. 28, 29). Figure 28 illustrates a large combined subsidence feature that includes a buried and active subsidence. This cross section shows a variety of depositional fills including cross bedding and onlapping fill. A characteristic pattern of fill and subsidence is shown in Figure 29. The plot of features observed from profiles (Fig. 30) shows two areas of concentration.

In general, when the lines cross it is an indication that the profiles have crossed different sections of one feature. This plot suggests that the profiles crossed different sections of two large (1000 m) subsidence sinkholes. One forms the northwest section of the lake and the other is in the southeast area. These may have developed independently and have coalesced over time. Lowry Lake has many of the same characteristic cover subsidence features found in Orange Lake, but at much larger scale.

A ground water monitoring well is located on the northwest shore of Lowry Lake. This is a Floridan aquifer well and is labeled as C-0439 on Figure 30. The natural gamma log (Fig. 31) of the well indicates the top of the Floridan aquifer is at -57 feet NGVD or approximately 80 milliseconds on the seismic data. The majority of resolvable data is above 40 milliseconds and so it cannot be determined if the entire confining unit is breached.

Magnolia Lake

Lake Magnolia is located one and a half kilometers southwest of Lowry Lake. Magnolia Lake is in Clay County and centered approximately at 29° 49' N and 81° 1' W. This lake is approximately one kilometer in diameter and is very similar in shape to Kingsley Lake.

The plot of the location along the profiles where the subbottom is disturbed by subsidence (Figure 30) indicates that the lake is formed by a single large subsidence feature. The features are continuous across the lake in both of the predominant traverse directions.

Figure 32 is a profile from Magnolia Lake that shows a shallow nearshore with a deepening towards a center containing a singular subsidence with onlapping fill on the northwest flank. In the central portion of the lake is an undisturbed surficial layer that is acoustically transparent and possibly high-organic "muck" or soft clayey sediments. The undisturbed surficial sediments implies that there has been little to no subsidence recently.

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