Engineering Geology

E n g i n e e r i n g G e o l o g y
Figure 3.21
Limestone pavement, the Burren, Southern Ireland.
Sinkholes are characteristic features of karst terrain and may develop where solutionopened
joints intersect (Waltham and Fookes, 2003). They may lead to an integrated
system of subterranean galleries and caves. The latter are characteristic of thick massive
limestone or dolostone formations. Sinkholes vary in diameter but usually are a few
metres or tens of metres across and may descend up to 500 m in depth below the surface
(Fig. 3.22).
Caves form in competent limestone or dolostone where there is an adequate through flow
of groundwater, the flow rate and aggressiveness of groundwater being mainly responsible
for the enlargement of caves. They originate along bedding planes and tectonic fractures,
which are enlarged into networks of open fissures, favourable flow paths being enlarged
selectively into caves. It is frequently asserted that the most active dissolution occurs
at and just below the water table (Trudgill and Viles, 1998). Hence, it is here, within the
uppermost part of the phreatic zone, where caves are most likely to be developed. As such,
they are often within 100 m of the ground surface. If the amplitude of fluctuation of the
water table increases or if it suffers a notable decline, this can lead to the enlargement of
caves. Subsequently, caves may be abandoned if their groundwater is captured by preferred
routes or they may be partially or wholly filled with sediment. The size of caves
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