The
River
Alyn, a major tributary of the Dee, flows over an area
of limestone rock near Mold. Limestone can be dissolved by
rainwater,
which create caves underground!
There
are
three cave systems near and beneath the River Alyn, close to
Loggerheads
Country
Park.
The
Disappearing
River For many
months
of the year the River Alyn seems to
dry up. So where does the water go? Watch
the
video below to find out!
The
dry
river bed of the Alyn
Video:
Where
does the river go? by Ian Adams,
UCET
The Underground World In
the limestone
rock near and beneath the River Alyn, the water has
eaten the rock away
to create a network of caves. Some of these have been
explored by
caving groups - and there are probably many more
waiting to be
discovered deep
beneath the ground!
Map
showing
the course of the River Alyn and the two
nearby caves Map overlay: Cris
Ebbs
and Marc Carney
Ogof
Hesp
Alyn (Cave
of
the Dry Alyn) This
cave is 2 km long, the longest in the
area, and was discovered in 1973.
Click
the
photo to enter the cave!
Ogof
Hen
Ffynnonau (Poacher's
Cave) This
cave is almost 1 km long, and has
some fascinating features,
including a gigantic stalagmite
base and
many fossils in the walls.
Click
the
photo to enter the cave!
Play
the
Video to
take
a trip down another
nearby
cave
HOW WERE THE CAVES
FORMED?
The
caves formed because the limestone rock in the area can
be dissolved by
water. Most cave systems in the world are found in
areas of
limestone. Limestone is a rock that is formed at the
bottom of oceans
from the
skeletons of small sea creatures.
A
map
showing where limestone can be found in North
Wales
An
animation
showing how a cave can be formed in limestone
The
caves
near the River Alyn were actually formed in ground that
was
completely
filled with
water: the rock was dissolved by the water to create
tube-like passages
(O-shaped). They are different from caves created
by water
running through rock as streams or rivers, as shown in
the animation
above - those caves are more V-shaped.
HOW WERE THE ALYN CAVES
DISCOVERED? From
the beginning of the twentieth century, water levels in
the area
dropped because a tunnel was built to drain water from
the many mines
in the area - this is the Milwr Tunnel, which runs for
10 miles to the
sea at Bagillt, and was begun in 1897.
When the water levels fell, the caves near the Alyn
drained of water
and could then be explored - but after heavy rain they
can completely
fill with water again!
The
Milwr
Tunnel, which drains the whole area
below ground. Today it still
carries 23 million gallons per day to
the sea, rising to 36 million
gallons in wet weather.
Click
HERE to find out
much more about
the Milwr tunnel.
Powell's
Lode
Cavern, a gigantic cave discovered while
building the Milwr Tunnel
-
no-one knows how deep it is!
It
is
the highest natural underground
chamber in Britain.
Limestone
Caves
The websites below are just a few of
those worth visiting to find out about the
spectacular world of
limestone caves.