Otter Hole
Encyclopedia
Otter Hole is perhaps one of the best decorated caves in Britain. Located on the English Welsh border just north of Chepstow
, the cave runs from the banks of the tidal River Wye
under the Chepstow Racecourse
and onwards through various chambers, each rich with cave formations. Due to its importance as one of the finest examples of decorated caverns in Europe access is restricted, managed by the Royal Forest of Dean Caving Club on behalf of the landowner.
through a gated doorway at the foot of a bluff. This is locked as a precaution against illegal entry to the cave, both to protect the rare forms inside the cave, and also to prevent anyone wandering into the cave and being trapped accidentally as the cave floods in sync with the tide.
After a short crawl with few squeezes the passage opens out to a 'beach' where the tidal sump
blocks access. At low tide this sump drains quickly and noisily, becoming passable as a 'duck' beneath a 'figure 8' double opening. Due to the frequency of the tidal sump two trips can be offered; a 'between tide trip' lasting around 6 hours will enter just after the sump drains and leave just before it fills, or the 'overtide trip' the sump is passed just before closing giving between 9 and 15 hours caving time.
Continuing past the sump a fairly linear route takes you along the active streamway, leading eventually to a pool in which many choose to 'wash off' a little; removing some of the thick estuarine mud that could otherwise sully the delicate formations. Passing a little further through a few boulder chokes brings you through many wonderfully decorated chambers and eventually to the Hall of 30. This is the largest of the chambers which is filled with very many monumental stalagmites in a range of colours from pure white, through oranges and yellows, to pure black. The range of colours is due to the variety of minerals seeping through the bedrock and deposited in the formations. Whites are the natural Calcium Carbonate forms, while elements such as Arsenic
create the black forms.
The formations continue beyond the Hall of 30 until the passage changes character once more at the junction of Tunnels Left and Right. Camp is generally considered to be the far back of the cave, again full of wonderful formations such as Straws
, Helictite
s and Pom Poms. The return journey takes you back through the Hall of 30 and along the streamway towards the sump.
The cave is a Site of Special Scientific Interest
(SSSI), GCR number 550.
Chepstow
Chepstow is a town in Monmouthshire, Wales, adjoining the border with Gloucestershire, England. It is located on the River Wye, close to its confluence with the River Severn, and close to the western end of the Severn Bridge on the M48 motorway...
, the cave runs from the banks of the tidal River Wye
River Wye
The River Wye is the fifth-longest river in the UK and for parts of its length forms part of the border between England and Wales. It is important for nature conservation and recreation.-Description:...
under the Chepstow Racecourse
Chepstow Racecourse
Chepstow Racecourse is a thoroughbred horse racing venue located just outside the town of Chepstow in Monmouthshire, Wales, near the southern end of the Wye Valley which forms the border with England...
and onwards through various chambers, each rich with cave formations. Due to its importance as one of the finest examples of decorated caverns in Europe access is restricted, managed by the Royal Forest of Dean Caving Club on behalf of the landowner.
Description
The entrance to the cave is situated on the banks of the WyeRiver Wye
The River Wye is the fifth-longest river in the UK and for parts of its length forms part of the border between England and Wales. It is important for nature conservation and recreation.-Description:...
through a gated doorway at the foot of a bluff. This is locked as a precaution against illegal entry to the cave, both to protect the rare forms inside the cave, and also to prevent anyone wandering into the cave and being trapped accidentally as the cave floods in sync with the tide.
After a short crawl with few squeezes the passage opens out to a 'beach' where the tidal sump
Sump
A sump is a low space that collects any often-undesirable liquids such as water or chemicals. A sump can also be an infiltration basin used to manage surface runoff water and recharge underground aquifers....
blocks access. At low tide this sump drains quickly and noisily, becoming passable as a 'duck' beneath a 'figure 8' double opening. Due to the frequency of the tidal sump two trips can be offered; a 'between tide trip' lasting around 6 hours will enter just after the sump drains and leave just before it fills, or the 'overtide trip' the sump is passed just before closing giving between 9 and 15 hours caving time.
Continuing past the sump a fairly linear route takes you along the active streamway, leading eventually to a pool in which many choose to 'wash off' a little; removing some of the thick estuarine mud that could otherwise sully the delicate formations. Passing a little further through a few boulder chokes brings you through many wonderfully decorated chambers and eventually to the Hall of 30. This is the largest of the chambers which is filled with very many monumental stalagmites in a range of colours from pure white, through oranges and yellows, to pure black. The range of colours is due to the variety of minerals seeping through the bedrock and deposited in the formations. Whites are the natural Calcium Carbonate forms, while elements such as Arsenic
Arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...
create the black forms.
The formations continue beyond the Hall of 30 until the passage changes character once more at the junction of Tunnels Left and Right. Camp is generally considered to be the far back of the cave, again full of wonderful formations such as Straws
Soda straw
A soda straw is a speleothem in the form of a hollow mineral tube. They grow in places where water leaches slowly through cracks in rock, such as on the roofs of caves...
, Helictite
Helictite
A helictite is a speleothem found in limestone caves that changes its axis from the vertical at one or more stages during its growth. They have a curving or angular form that looks as if they were grown in zero gravity...
s and Pom Poms. The return journey takes you back through the Hall of 30 and along the streamway towards the sump.
Conservation
Because of the unique collection of formations at Otter Hole access is limited, with bookings for trips taken well in advance through the Otter Hole Secretary. Those taking part in trips may well be asked to participate in some of the conservation work that is carried out, such as cleaning the stals and drapes, laying tape or simply cleaning up any rubbish found. All trips are run with a warden from the Royal forest of Dean Caving Club, who are there to both guide and control impact on the area.The cave is a Site of Special Scientific Interest
Site of Special Scientific Interest
A Site of Special Scientific Interest is a conservation designation denoting a protected area in the United Kingdom. SSSIs are the basic building block of site-based nature conservation legislation and most other legal nature/geological conservation designations in Great Britain are based upon...
(SSSI), GCR number 550.