The landscape
in Krabi Province in southern Thailand is characterized by steep, limestone
headland cliffs along its shoreline and by limestone (karst) towers both
offshore from the headlands and inland along its alluvial plains. The coastal
karst towers rise directly out of the shallow waters of Phang Nga Bay or
emerge from mangrove-fringed tidal flats whereas the inland karst towers
are surrounded by Quaternary alluvial and colluvial deposits.
The tower
karst in Krabi is developed in massive Permian limestone and dolomitic
limestone of the Ratburi Group. These folded carbonate beds strike northeast-southwest
and dip gently to moderately to the northwest and southeast.
Two varieties
of tower karst are prominent in the Krabi region, peak forest karst (isolated
peaks) and peak cluster karst (group of peaks with a common rocky base).
In the peak forest karst the most common peak shapes are tall, vertical-sided,
cylindrical-shaped towers (Turm karst) and moderately steep-sided, cone-shaped
towers (Kegel karst). The peak forest towers have maximum elevations that
range from about 60 to 210 meters above mean sea level. The peak cluster
karst exhibits cone- and cylindrical-shaped peaks on broad masses of limestone.
Some of these masses are elongated along the northeast-southwest direction
of strike of the Ratburi Limestone and often have vertical cliff faces
along their margins. The maximum elevations of the peak cluster towers
range from about 240 to 400 meters above mean sea level.
In some locations
the cylindrical- and cone-shaped towers occur adjacent to each other. This
morphology supports the argument that peak shape of tower karst is controlled
mainly by lithologic factors (e.g., massiveness of beds and porosity) rather
than climatic factors. The evolution of the cylindrical-shaped towers is
also maintained by spalling of tower walls.
The lower
maximum elevations of the peak forest karst and its relative spatial proximity
to the peak cluster karst suggest that the peak forest evolved from the
peak cluster as a later stage of karst landform development. However, late
Quaternary sea level changes have also influenced karst development in
the Krabi region by exerting controls on fluvial erosion-deposition cycles,
water tables, and supply of allogenic surface waters.