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Open File Report:
Seismic Reflection
Surveys |
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Lowry & Magnolia Lakes |
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Lowry Lake
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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. |
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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