Page 213 - Fundamentals of Geomorphology

196 PROCESS AND FORM

Papua New Guinea and Mount Api in Sarawak, consists semi-arid areas. Smaller-scale versions are known from
of bare, net-like, saw-topped ridges with almost verti- the Nahanni limestone karst region of the Mackenzie
cal sides that stand up to 120 m high. The spectacular Mountains, Canada (Brook and Ford 1978). Here, the
ridges rise above forest-covered corridors and depres- labyrinth karst is stunning, with individual streets longer
sions. They seem to have formed by limestone solution than 1 km and deeper than 50 m (Plate 8.6).
without having previously been buried.
Coastal karren
Ruiniform karst Around coasts and lakes, limestone or dolomite outcrops

This is an assemblage of exceptionally wide grikes and often display a distinctive solutional topography, with
degrading clints that have been exposed by soil erosion features including intertidal and subtidal notches (also
(Plate 8.5).The clints stick out like ‘miniature city blocks called nips; Plate 8.7) and a dense formation of pits,
in a ruined townscape’ (Ford and Williams 1989, 391). pans, micropits, and spikes (Plate 8.8). Boring and graz-
Ruiniform karst is found in the French Causses, where ing organisms may help to form coastal karren, as may
deforestation and soil erosion have occurred. On high
crests, ruiniform karst is transitional to limestone tors.

Corridor karst

In places, grikes grow large to form a topography of
aligned or criss-crossing corridors. The large grikes are
called bogaz, corridors, zanjones, and streets. Grike-wall
recession produces square-shaped or box valleys and large
closed depressions called platea. Corridor karst land-
scapesarecalledlabyrinth karst,corridor karst,orgiant
grikeland.Itislarge-scaleclint-and-griketerrainbutmay
have a complex history of development. Grikelands form
under tropical and temperate rainforest and in arid and

Plate 8.6 View of Nahanni labyrinth karst, showing
Plate 8.5 A ruiniform assemblage (residual clint blocks) in intersecting networks of karst streets interspersed with
flat-lying limestones near Padua, Italy. karst platea.
(Photograph by Derek C. Ford ) (Photograph by George A. Brook)