Karst: What is it?
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What is karst?
Karst is a unique landscape formed by the underground erosion of rocks such as limestone and marble that dissolve in water. Rainwater, made acidic by carbon dioxide from the atmosphere and soil, slowly infiltrates cracks in limestone and marble, dissolving the rock and enlarging the openings. If these openings become large enough for humans to enter, they are termed caves. Caves, however, form only a tiny part of most karst areas. Karst openings support unique ecosystems that include plants, bacteria, crickets, spiders, fish, and small mammals adapted to this dark but little changing environment.
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A vulnerable landscape Caves and karst develop slowly over tens of thousands of years or longer. Areas of karst landscape require careful management, as sensitive underground features can be damaged by surface activities such as road building or logging which alter the underground flow of water and air.
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WHAT KARST COMES BEFORE CAVES?
Karst is a landscape or terrain that results from the weathering of
bedrock types that are soluble in water. These
bedrock types are primarily limestone and marble, but can also include:
dolomite, gypsum and halite. The
karst landscape is characterized by both a lack of surface streams and a
subsurface network openings. Some
of these subsurface openings can be entered by humans, and are considered as
caves -- the best known features of the karst system. However, caves form only a small part of the karst ecosystem,
which includes all living and non-living components of the karst landscape.
Non-living components include soil and bedrock, along with air, water and
energy that is easily transferred between the surface and subsurface
environments. Karst sustains specialized
life forms, ranging from calcareous-loving plants growing on exposed
bedrock surfaces to unusual animals (or troglobites) living in the subsurface
beyond the twilight zone.
WHY
WE SHOULD CARE ABOUT KARST?
The
subsurface component of the karst system under natural conditions is a stable environment
that has developed over thousands of years, with consistent
temperatures and humidity all year round. Unusual fauna that develop in this
light deficient environment range from bacteria, crustaceans, spiders, fish and
small mammals. These ecosystems are very sensitive to change. Changes in water
percolation and air flow can significantly alter these stable environments
effecting both life forms and the rates of bedrock dissolution.
Karst offers opportunities for scientific study and education, allowing
us a window into past environments that may not have changed for thousands of
years. These can potentially
include undisturbed archaeological sites and well preserved animal remains.
HOW
SHOULD WE MANAGE KARST?
Most
of the present urban centres on Vancouver Island are situated away from areas
underlain by karst. However, in other parts of the world (e.g.China, Southeast
US) living on top of the karst landscape can present some special problems such
as ground subsidence, contamination of groundwater, and damage to cave
ecosystems. On Vancouver Island, the principal concern is the impact of forest
development activities on karst. These impacts can range from the intersection
of shallow caves and the re-direction of water flow during forest construction
to logging around sensitive features (e.g., cave entrances) and areas where thin
soils might be displaced into vertical solutional openings or epikarst. Methods
are presently being developed to assess both the surface and sub-surface of the
karst landscape in forested areas and to assess their likelihood for change by
external development, which is termed vulnerability. The greater the vulnerability of
the landscape the more restrictive the management practices required.
