CLASSICAL THEORIES OF CAVERN DEVELOPMENT
(This Section is taken from Reeder, 1988)
For much of this century one of the most
intensive debates in the science of geomorphology has dealt with the origin of
limestone caves. Do caves form above the water table (vadose zone), below the
water table (phreatic zone), or at the plane of the water table itself? The
various theories can be classified as follows:
1. Vadose Theories – Dwerry house (1907), Greene (1908), Matson (1909), and Malott (1937)
have maintained that most cavern development takes place above the water table
where groundwater velocity is greatest. Thus, fast flowing underground streams,
which combine mechanical corrosion with carbonate solution, are responsible for
cave development. Martel (1921) believed that the importance of flow in caves
and conduits is so great that it is irrelevant to regard cavernous limestone as
possessing a water table, in the sense of a single surface below which the rock
is entirely saturated.
2. Deep Phreatic Theories – Cvijic (1893), Grund (1903), Davis (1930) and Bretz (1942) have
argued that cave initiation and most cavern enlargement occur at random depth
below the water table, often in the deep phreatic zone. The caves are enlarged
by the corrosive effects of slowly moving phreatic water. A second cycle of
cavern development may occur when the water table has been lowered by surface
denudation, thus draining the caves of ground water and permitting vadose water
and air to enter the cave. During the second cycle surface streams may enter an
existing cavern system and alter cave passages somewhat by corrosion.
3. Shallow Phreatic or Water Table
Theories – Swinnerton (1932), Rhoades and Sinacori (1941),
and Davies (1960) have supported the idea that rapidly moving water at the
water table is responsible for the solution of most caves. The elevation of the
water table fluctuates with variations in the volume of groundwater flow, and
there may be substantial cave development within a narrow zone above and below
its mean position. However, the mean position of the water table must remain
relatively constant for long periods. To explain multi-leveled cave systems a
stationary water table has often been associated with periods of landscape base
leveling followed by periods of rejuvenation with rapid down-cutting to the
next base level.
Although most speleologists would probably agree that all three of the
above theories are applicable in some instances, most would argue that the
great majority of caves are formed at or near the water table. Subterranean
stream invasion, normally classified as a vadose theory, has had few advocates
down through the years. Malott (1937) concluded that the large caverns of
southern Indiana resulted from surface streams being diverted underground and
developing caverns at or near the water table. Malott (1952) cited the Lost
River of Indiana as a good example of subterranean invasion by a surface flowing
stream. Woodward (1961) and Howard (1963), and Crawford (1978; 1987) are
prominent among others who have advocated the invasion theory of cavern
development.
In discussing the hydrology of limestone terrains Smith, Atkinson and
Drew (1976) suggest that the debate on the nature of limestone drainage has
been between two main schools of though rather than three.
One school, taking its ideas from Grund (1903), has maintained that water
circu1ation in limestones is essentially similar to that of any other fractured
rock, and that caves develop as a consequence of the circulation without
greatly influencing its pattern (see, for example, Davis, 1930; Swinnerton,
1932; Rhoades and Sinacori, 1941). On the other hand, the school following
Martel (1910) tends to rnaintain that without caves and conduits there can be
no underground circulation, or virtually none, and that the groundwater regime
of limestone terrains is thus utterly different from that of other rocks
(Trombe,1952). (Ford and Cullingford, 1976, p. 209).
They conclude that the two apparently opposing models of Grund and Martel
are but extreme cases of a spectrum of possible drainage systems and that most
limestone regions exhibit features of both schools of thought, while areas that
show either to the exclusion of the other are rare.
A major problem with the classical theories of cave origin is the minor
role assigned to the structural, stratigraphic, topographic, and hydrologic
setting. It now appears obvious that no one theory of cavern origin and
development can be applicable to all caves. Ford (Ford and Cullingford, 1976)
maintains that since no two geological situations are ever exactly the same, a
single generalized theory of speleogenesis is not possible. Although many
factors may be common to many areas their relative importance will depend on
the geological situation and therefore every area will have its own unique
speleogenetic history.
However, since there are areas with very similar geological situations,
it is believed that very generalized models of speleogenesis can be developed
for areas that have a similar structural, stratigraphic, topographic and
hydrologic setting.