Geology Reference
In-Depth Information
Fig. 1. Location of Gibraltar, St. Michaels cave and other features described in the text. Figure adapted from Mattey
et al. (2008).
below sea level suggesting that initial phases of
dissolution may have taken place by mixing near
the freshwater-seawater interface via processes
similar to flank margin cave formation (Mylroie
& Carew 1988; Romanov & Dreybrodt 2006).
Wave-cut platforms (90 and 130 m asl) are a promi-
nent feature of the geomorphology of Gibraltar
(Rodriguez-Vidal et al. 2004) recording higher
stands of sea level in the past, and although the
age and development history of Gibraltar caves
are not yet well understood, solution voids and
their subsequent decoration by speleothem depo-
sition may be controlled by neotectonic uplift in
conjunction with sea level fluctuations between
glacial and interglacial periods (Rodriguez-Vidal
et al. 2004).
OSM has a number of natural entrances as well
as artificial high and low level tunnels used for
tourist
natural chimney ventilation (Wigley & Brown
1976; Atkinson et al. 1983) between high- and
low-level entrances and is known to show seasonal
reversals in flow direction. In winter, warm cave
air flows upwards drawing cool outside air into the
lower entrances whereas in summer cave air flows
out of lower entrances, drawing atmosphere
into upper entrances. Before modern development
for tourism the natural entrances would all
have been at a higher level and chimney ventilation
may not have been as strong a feature as it is
at the present time. The NSM cave system has no
known natural entrances and remained unconnected
to OSM until the link was made in 1942 with
the lowest part of main show cavern. Season-
ally reversing chimney ventilation can also be
detected though the 1 m 2 trapdoor link between
OSM and NSM, although sealing this connection
for
access.
The
showcave
develops
strong
one
month
in
August
2006
was
found
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