Geology Reference
In-Depth Information
The nomenclature devised by Joe Jennings (1971, 1985)
brings some sense of order to a multilingual lexicon
of confused and inconsistent usage. The basic forms
are divided according to the degree of cover by soil
and vegetation - bare ('free karren'), partly covered
('half-free karren'), and covered ('covered karren') (Bögli
1960). The bare forms are divided into those produced
by surface wetting and those produced by concentrated
surface runoff. Derek Ford and Paul Williams (1989,
376-7) offered a purely morphological classification of
karren types because current understanding of karren-
forming processes is too immature to build useful genetic
classifications. However, their scheme, although using
morphology as the basis for the major divisions, uses
genetic factors for subdivisions. Jennings's classification
underpins the following discussion, but a few types
mentioned by Ford and Williams, and their 'polygenetic'
class, are included (Table 8.2).
Bare forms
Bare forms produced by surface wetting comprise
pits
,
ripples
,
flutes
,
bevels
, and
runnels
, all of which are
etched into bare limestone by rain hitting and flowing
over the naked rock surface or dripping or seeping on
to it. They are small landforms, the smallest,
micropits
and
microrills
, being at most 1 cm wide and deep, and
the largest,
solution flutes
(
Rillenkarren
), averaging
about 1.0-2.5 m wide and 15 m long. The small-
est features are called
microkarren
. Solutional features
of a few micrometers can be discerned under an elec-
tron microscope. Exposed karst rocks may develop relief
Table 8.2 Small limestone landforms produced by solution
Form
Comment
Bare limestone forms (surface wetting)
Micropits and etched surfaces
Small pits produced by rain falling on gently sloping or flat bare rocks
Microrills
Rills no deeper or wider than about 1.0 mm and not longer than a few
centimetres. Called
Rillenstein
when formed on stones and blocks
Solution ripples or fluted scallops
Shallow, ripple-like flutes formed on steep to vertical surfaces by flowing
water normal to the direction of water flow. Prominent as a component of
cockling patterns (a mixture of scallops, fluted scallops, or ripples) on
steep and bare slopes
Solution flutes (
Rillenkarren
)
Longitudinal hollows that start at the slope crest and run down the maximum
slope of fairly steep to vertical rock surfaces. They are of uniform fingertip
width and depth, with sharp ribs between neighbouring flutes. May occur
with rippling to give the rock a netted appearance
Solution bevels (
Ausgleichsflächen
)
Very smooth, flat or nearly so, forming tiny treads backed by steeper, fluted
rises. A rare variant is the solution funnel step or heelprint (
Trittkarren
or
Trichterkarren
)
Solution runnels (
Rinnenkarren
)
Solution hollows, which result from Hortonian overland flow, running down
the maximum slope of the rock, larger than solution flutes and increasing
in depth and width down their length owing to increased water flow. Thick
ribs between neighbouring runnels may be sharp and carry solution flutes
Decantation runnels
Forms related to solution runnels and including meandering runnels
(
Mäanderkarren
) and wall solution runnels (
Wandkarren
). Produced by the
dripping of acidulated water from an upslope point source. Channels
reduce in size downslope
Decantation flutings
Packed channels, which often reduce in width downslope, produced by
acidulated water released from a diffuse upslope source
Continued
