Lineament Analysis - Rock Fractures
The following is reproduced by permission of the United States Army Corps of Engineers, from a 2004 report
on Lineament Analysis in South Florida.
Studies of lineaments (photolinears) discernable on aerial photographs have revealed that these linears are
abundant natural, and are systematically oriented in four principal groups of external stresses in the WNW,
NNW, NNE, and ENE directions. Fractures are formed predominately by terrestrial or earth tides due to
gravitational effects of the moon and sun, tectonic forces, diagenetic, or weathering processes (Blanchet,
Numerous investigations have shown that most of the fractures and faults identified as photolinears are
vertical or near-vertical zones of fracture concentrations (Kaiser, 1950; Blanchet, 1957; Lattman, 1958;
Lattman and Matzke, 1961; Lattman and Parizek, 1964).
The following paragraphs present excerpts of a good summary on fracture-trace mapping principles by Diodato
Photolinear analysis is a type of remote sensing analysis wherein investigators map linear features (photolinears)
observable on aerial photographs or other remotely-sensed images. The use of photolinears for ground-water
well siting was pioneered by Lattman and Parizek (1964). For linear features of geologic origin, lineaments
are defined as those photolinear features greater than one mile in length, whereas fracture traces are the
same type of feature having a total length of less than one mile. The width of these zones of fracture
concentration can vary from a few to tens of meters. In general, longer lineaments tend to have wider surface
expressions of the zone of fracture and wider zones of fracture concentration at greater depths. Because the
fracture trace is the surface expression of the vertical zone of fracture concentration, Parizek has suggested
the "fracture zone trace" might be a more appropriate descriptive term (Parizek and Diodato, 1995).
Zones of fracture concentration in soluble rocks such as carbonates and evaporates can lead to enhanced
dissolution of these rocks due to accelerated chemical and physical weathering. In the case of rocks prone to
karstification, White (1999) has determined that the development of karst conduits begin when fracture
apertures reach about one centimeter.
In south Florida, linear features (photolinears) are detected and identified based primarily upon
indicators such as aligned solution depressions, surface ponds, vegetation, and variations in soil tone (Trainer
and Ellison, 1967, Parizek, 1975). Doline (sinkhole) development can be expected to follow orientation of
photolinears, as these represent areas of higher permeability and porosity.
In 1973, the U.S. GEOLOGICAL SURVEY completed the Water-Resources Investigations Report, I-73,
GEOHYDROLOGY OF THE CROSSFLORIDA BARGE CANAL AREA WITH SPECIAL REFERENCE TO THE OCALA VICINITY (Prepared in
cooperation with: U.S. DEPARTMENT OF THE ARMY CORPS OF ENGINEERS). The Foundation is indebted to the author,
Glen L. Faulkner, for illustrating the importance of understanding the geological influences upon ground
water flows in an aquifer system. The two figures 17 and 22 from the report are included to underline the
relationship between potentiometric flows and conduit flows along fracture sets and fault lines which are
Mapping the fracture lineaments in the Ocala vicinity aids in determining principal directions and routes
of ground-water in the Floridan Aquifer. The writer and others have observed that most caverns and solution
channels in the limestone are oriented along near-vertical fractures having trends of fracture systems mapped
at the surface. The logical inference is that water moving through the aquifer tends to follow the line of
least resistance or greatest permeability, which in this case is along the fractures. In general, the greatest
solution of limestone at shallow depths below the water table takes place where the greatest amount of water
moves through. Thus cavities are developed as the walls of fractures are dissolved away by recently recharged
ground water with a high carbon dioxide (CO2) content. Refer to the I – 73 report p43.
The fault system, (as also is the case with Crystal River/Kings Bay, see NOTE below), apparently
controls the rectilinear course of the Oklawaha River, and it lowered the geologic section east of Ocala and
Silver Springs. Poorly permeable strata in the Hawthorn are preserved in the structurally lowered river valley,
but were removed by erosion from the higher areas to the west. Therefore, the Floridan Aquifer is confined in
the down-faulted area, and is more or less unconfined in the structurally high area to the west.
Structural dip of the strata in the Barge Canal area, even though very low, is thought to play an important
role in the occurrence of Rainbow Springs. The Springs issue from points at or near the contact between the
lower member of the Ocala Limestone and the underlying Avon Park Limestone just off the crest of the Ocala
Uplift down the northeast flank of the structure. Although faulting may be significant among the reasons for
the springs’ occurrence (fig. 17), the writer believes that the permeability of the upper part of the
Avon Park is sufficiently low to produce a barrier at the base of the highly permeable Ocala Limestone. Thus,
as the contact between the Avon Park and Ocala approaches the surface up the northeast flank of the Ocala
Uplift, the large volume of ground water moving southward through the highly permeable Ocala Limestone
[Foundation's emphasis], is too great to be conducted by the less permeable Avon Park as the
overlying Ocala wedges out and the flow is discharged at the surface. On the other hand, faulting is
one of the most important geologic factors causing Silver Springs. [Foundation's Emphasis]
Apparent downfaulting east of the springs has placed poorly permeable beds of the Hawthorn Formation in
position as a barrier to eastward flow in the Floridan Aquifer, thus maintaining a high enough potentiometric
surface at the spring site to cause overflow from open limestone caverns and sinkholes. The geohydrologic
relationships at the two springs sites are illustrated in part in section X-X’, Refer to Figure 10 in
the I – 73 report, p46.
From p 60 of the I-73 report, referring to Figure
22: Ground water moves downgradient from the potentiometric highs toward the saddle and to the
peninsular coasts along flow paths approximately perpendicular to the equipotential lines [Foundation's
emphasis]. Ground-water drainage basins in the upper part of the aquifer may be outlined on the map by
drawing lines along potentiometric divides. Thus, it is possible to demonstrate the spatial relationship of
the canal route to the ground-water flow pattern and to delineate the drainage areas of Rainbow and Silver
Springs. The mapped potentiometric surfacean imaginary surface defined by the level to which water in an aquifer would rise in a well due to the natural pressure in the rocks. is assumed to represent that part of the aquifer supplying the springs. A knowledge of the size
and shape of the drainage areas of the two springs is essential to the quantitative analysis of aquifer
characteristics along critical reaches of the canal.
The general configuration of the potentiometric surface changes little from one(dry/wet) season to
the other, even though the surface is several feet higher and gradients tend to be somewhat steeper in the
high-water period. The most interesting change is in an area northwest of Ocala where the ground-water
drainage divide between Silver and Rainbow Springs appears to shift several miles westward during the change
from the low- to the high-water period.
In addition to showing general directions and preferential routes of ground-water flow, the maps of the potentiometric surfacean imaginary surface defined by the level to which water in an aquifer would rise in a well due to the natural pressure in the rocks. help to demonstrate important geohydrologic relationships in the area. For instance, the
configuration of the potentiometric surface tends to confirm routes of concentrated groundwater flow
suggested by the fracture trace maps [Foundation's emphasis] , thickness of cover map,
and top-of-rock map (figs. 15, 18, and 19 of the I-73 report). Conversely, the geologic maps are
useful interpretive tools in estimating the potentiometric surfacean imaginary surface defined by the level to which water in an aquifer would rise in a well due to the natural pressure in the rocks. in areas of sparse water-level control, and for interpreting the anomalies on the potentiometric
surface. The foregoing relationships are discussed later in this report.
[See I - 73 pp 68/9 and Vernon, R.O., 195l, Geology of Citrus and Levy Counties, Florida: Florida
Geological Survey Bulletin 33, 256 p].
"Here's the figure that inserts at page 48 in the R.O. Vernon bulletin, it looks
to be a much smaller scale than in the Faulkner report, so it shows all of Citrus County and regions to the
south. Again, these are only the major lineament features interpreted to be bedrock fractures or jointing,
and joint spacings can be much closer together, although there are probably dominant fractures that act as
significant conduits for groundwater movement." Comment by David DeWitt P.G. ,Southwest Florida Water
It is clear from the late R.O. Vernon's paper of 1951, (Figure
40, and page 242) that a convergence of potentiometric (piezometricA measure of pressure of water, especially in an aquifer. Shows altitude at which water would have stood in a tightly cased well relative to a given sea level. See also potentiometric surface.)
flows from the north and the south tending towards the Gulf Coast, occurs in Citrus County. The fracture sets
converging in Citrus County, in essence, assist these convergent flows. This is particularly and uniquely the
case where the springs serving Crystal River/Kings Bay are concerned.
With regard to the source of fresh water to Crystal River/Kings Bay, it is more than likely that the NNE
to SSW fracture set shown in Figure
17, which runs from Ocala, extends all the way to Hunter Spring run to feed the spring group in that
region of Kings Bay. (It is thought that the shown early termination of this fracture might well coincide with
the lack of aerial photographs referred to by Vernon on page 47 of his 1951 paper, and being obscured by the
overburden of the Brookesville Ridge). This would be the case if that fracture set were to bear the same
characteristic length as those other orthogonals depicted on the Figure 11 mapping on which the Figure 17 is
The fracture sets and equipotential lines (piezometric lines) pre-date the formation of Lake Rousseau by
many centuries. Potentiometric flow from the high to the north of the Lake Rousseau would appear to merge with
the flow originating to the east and south of the Rainbow River in the area of northeast Citrus County. This
would also appear to strengthen the ground water stream along the fracture set passing through that area
leading southwestward to the Hunter Spring / Three Sisters Spring group.
The angular transitions of the general flow line of Crystal River would appear to follow the fracture sets
along its path, as predicated by Vernon. Flowing NNW from its origin with the springs in the south region of
Kings Bay, turning more westerly as it is joined by flows from Hunter Spring run, then more northerly as
joined by the fracture set running parallel to and set to the west of the initial Kings Bay direction, and on
out to the Gulf.
On page 111, of the I-73 report, Dr Faulkner writes: "Additional geological information should be
gathered by examination of good sets of lithologic samples available from test holes and wells. Various remote
sensing methods, such as aerial infrared and color photography, should be investigated and utilized where
possible to aid in the delineation of certain stratigraphic and structural characteristics of the area, the
knowledge of which may help to further define routes of preferential ground-water flow, and thereby
aid in preventing pollution of water in the aquifer. [Foundation's emphasis]"
Click for a discussion of Karst features.