Hell Kettles 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...

 in the Darlington

Darlington (borough)

Darlington is a local government district and borough in North East England. In 2008 it had a resident population of 100,500 It borders County Durham to the north and west, North Yorkshire to the south along the line of the River Tees, and Stockton-on-Tees to the east.-Council:Traditionally part of...

 district of County Durham

County Durham

County Durham is a ceremonial county and unitary district in north east England. The county town is Durham. The largest settlement in the ceremonial county is the town of Darlington...

, England

England

England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

. It was designated for its biological interest as the only site in County Durham where there is a body of water fed by springs

Spring (hydrosphere)

A spring—also known as a rising or resurgence—is a component of the hydrosphere. Specifically, it is any natural situation where water flows to the surface of the earth from underground...

.

Location

The site, which lies on the floodplain

Floodplain

A floodplain, or flood plain, is a flat or nearly flat land adjacent a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge...

 of the River Tees

River Tees

The River Tees is in Northern England. It rises on the eastern slope of Cross Fell in the North Pennines, and flows eastwards for 85 miles to reach the North Sea between Hartlepool and Redcar.-Geography:...

, to the south of Darlington, is situated alongside the A167

A167 road

The A167 is a road in North East England. Most of its route was formerly the A1 as most of it is the original route of the Great North Road until the A1 was re-routed with the opening of the A1 in the 1960s....

, about 1 mile south of the junction of that road with the A66

A66 road

The A66 is a major road in northern England which in part follows the course of the Roman road from Scotch Corner to Penrith. It runs from east of Middlesbrough in the ceremonial county of North Yorkshire to Workington in Cumbria...

.

Origin

The Kettles are two pools that are the end result of catastrophic subsidence in 1179: the Permian rocks underlying the area include substantial thicknesses of evaporite

Evaporite

Evaporite is a name for a water-soluble mineral sediment that result from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporate deposits, marine which can also be described as ocean deposits, and non-marine which are found in standing bodies of...

s—gypsum

Gypsum

Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...

 and gypsiferous mudstone

Mudstone

Mudstone is a fine grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.0625 mm with individual grains too small to be distinguished without a microscope. With increased pressure over time the platey clay minerals may become aligned, with the...

—and subsidence resulting from subterranean dissolution of these beds is a frequent occurrence, though the scale of the Hell Kettles subsidence is exceptional. Surface runoff

Surface runoff

Surface runoff is the water flow that occurs when soil is infiltrated to full capacity and excess water from rain, meltwater, or other sources flows over the land. This is a major component of the water cycle. Runoff that occurs on surfaces before reaching a channel is also called a nonpoint source...

 and seepage from calcareous

Calcareous

Calcareous is an adjective meaning mostly or partly composed of calcium carbonate, in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.-In zoology:...

 springs

Spring (hydrosphere)

A spring—also known as a rising or resurgence—is a component of the hydrosphere. Specifically, it is any natural situation where water flows to the surface of the earth from underground...

 has created the two pools, one of which is the only body of spring-fed open water in County Durham: there were originally four subsidence depressions, but one filled in and two are now linked in a pond aptly named 'Double Kettle'.

The name "hell-kettle" is often applied to ponds that are popularly believed to be bottomless; these particular ponds are mentioned in Holinshed

Raphael Holinshed

Raphael Holinshed was an English chronicler, whose work, commonly known as Holinshed's Chronicles, was one of the major sources used by William Shakespeare for a number of his plays....

's Chronicles:

and, it has been suggested, may have inspired the scene in Lewis Carroll

Lewis Carroll

Charles Lutwidge Dodgson , better known by the pseudonym Lewis Carroll , was an English author, mathematician, logician, Anglican deacon and photographer. His most famous writings are Alice's Adventures in Wonderland and its sequel Through the Looking-Glass, as well as the poems "The Hunting of the...

's Alice's Adventures in Wonderland

Alice's Adventures in Wonderland

Alice's Adventures in Wonderland is an 1865 novel written by English author Charles Lutwidge Dodgson under the pseudonym Lewis Carroll. It tells of a girl named Alice who falls down a rabbit hole into a fantasy world populated by peculiar, anthropomorphic creatures...

in which Alice tumbles down a rabbit hole.

Ecology

Despite their proximity, the two pools differ ecologically. 'Double Kettle' is fed by surface runoff and its water is turbid, supporting only an impoverished surface vegetation of pondweeds, including the alien Canadian pondweed, Elodea canadensis; it is fringed mainly by common reed, Phragmites australis, with some saw-sedge and common club-rush, Scirpus lacustris.

To the south, the smaller 'Croft Kettle' is fed by calcareous subterranean springs and its clear water supports a luxuriant growth of stoneworts; its fringing swamp is dominated by saw-sedge, Cladium mariscus

Cladium mariscus

Cladium mariscus is a species of flowering plant in the sedge family known by the common name Saw-sedge or Sawtooth Sedge. It is native of temperate Europe and Asia where it grows in base-rich boggy areas and lakesides. It can be up to 2.5 metres tall, and has leaves with hard serrated edges....

, creating a vegetation type similar to that of the fens of East Anglia

East Anglia

East Anglia is a traditional name for a region of eastern England, named after an ancient Anglo-Saxon kingdom, the Kingdom of the East Angles. The Angles took their name from their homeland Angeln, in northern Germany. East Anglia initially consisted of Norfolk and Suffolk, but upon the marriage of...

 and which is found nowhere else in County Durham.

The area around the ponds is mainly damp grassland, with a rich variety of sedges, Carex spp

Carex

Carex is a genus of plants in the family Cyperaceae, commonly known as sedges. Other members of the Cyperaceae family are also called sedges, however those of genus Carex may be called "true" sedges, and it is the most species-rich genus in the family. The study of Carex is known as...

.