pastoralists to move their herds to use the plentiful winter grasses that grow in the
joints of the limestone; these grasses are active because the microclimatic heating
in the joints is greater in the winter than in the lowland surroundings.
Urban areas are at some risk because large sinkholes sometimes open under the
weight of human surface modification. Parts of Florida offer many examples of
this phenomenon. Even after a building or road has been in existence for many
years, the mass of the construction can collapse the roofs of cavities, especially
in times of drought when the water table is low. Florida’s houses, roads, and car
dealerships have been swallowed from time to time.
The relatively free flow of surface water into the groundwater makes ground-
water quite susceptible to contamination from the surface. This pollution can
spread many times more quickly than in other bedrock structures and becomes a
potential hazard as water is tapped from wells and springs. Because of such diffi-
culties, karst areas are frequently thinly settled compared to their surroundings.196 Karst