Page 226 - Fundamentals of Geomorphology

KARST LANDSCAPES 209

a
() SUBTERRANEAN KARST FORMS
Waters from streams sinking into limestone flow through
a karst drainage system – a network of fissures and
conduits that carry water and erosion products to springs,
where they are reunited with the surface drainage sys-
() tem. In flowing through the karst drainage system, the
b
water and its load abrade and corrode the rock, helping to
produce cavern systems.These subterranean landforms
contain a rich variety of erosional and depositional forms.

Erosional forms in caves
()
c
Caves are natural cavities in bedrock. They function as
conduits for water flowing from a sink or a percolation
point to a spring or to a seepage point (Figure 8.17). To
form, caves need an initial cavity or cavities that channel
the flow of rock-dissolving water. The origin of these
cavities is debatable, with three main views taken:
Figure 8.16 Proposed sequence of events leading to
‘bollard’ rock formation in quartzitic sandstone, 1 The kinetic view sees tiny capillaries in the rock
north-central Thailand. (a) Polygonal cracks develop in a determining the nature of flow – laminar or turbu-
case-hardened surface that act as avenues of weathering. lent. In capillaries large enough to permit turbulence,
(b) Weathering deepens the cracks, forming a convex
surface on each polygonal block. (c) Further weathering ahelicalflowacceleratessolutionofthecapillarywalls
removes the edges of the polygonal blocks and deepens and and positive feedback does the rest to form a principal
widens the cracks. cave conduit.
Source: Adapted from Robinson and Williams (1992) and 2 The inheritance or inception horizon view envi-
Doerr (2000) sions a pre-existing small cavity or chain of vugs,

Plate 8.15 Kukenan Tepui, Venezuela.
(Photograph by Stefan Doerr)