Dartmoor

Dartmoor is an upland area in southern Devon, England. The moorland and surrounding land has been protected by National Park status since 1951. Dartmoor National Park covers .

The granite which forms the uplands dates from the Carboniferous Period of geological history. The landscape consists of moorland capped with many exposed granite hilltops known as tors, providing habitats for Dartmoor wildlife. The highest point is High Willhays, above sea level. The entire area is rich in antiquities and archaeology.

Dartmoor National Park is managed by the Dartmoor National Park Authority, whose 22 members are drawn from Devon County Council, local district councils and Government.

Parts of Dartmoor have been used as military firing ranges for over 200 years. The public is granted extensive land access rights on Dartmoor (including restricted access to the firing ranges) and it is a popular tourist destination.

Physical geography

Geology

Dartmoor includes the largest area of granite in Britain, with about at the surface, though most of it is under superficial peat deposits. The granite (or more specifically adamellite) was intruded at depth as a pluton into the surrounding sedimentary rocks during the Carboniferous period, probably about 309 million years ago. It is generally accepted that the present surface is not far below the original top of the pluton; evidence for this includes partly digested shale xenoliths, contamination of the granite and the existence of two patches of altered sedimentary rock on top of the granite.
A considerable gravity anomaly is associated with the Dartmoor pluton as with other such plutons. Measurement of the anomaly has helped to determine the likely shape and extent of the rock mass at depth.

Tors

Dartmoor is known for its tors – hills topped with outcrops of bedrock, which in granite country such as this are usually rounded boulder-like formations. More than 160 of the hills of Dartmoor have the word ''tor'' in their name but quite a number do not. However, this does not appear to relate to whether or not there is an outcrop of rock on their summit. The tors are the focus of an annual event known as the Ten Tors Challenge, when around 2400 people aged between 14 and 19 walk for distances of 56, 72 or 88 km (35, 45 or 55 mi) between ten tors on many differing routes.

The highest points on Dartmoor are on the northern moor: High Willhays, , () and Yes Tor, , () The highest points on the southern moor are Ryder's Hill, , (), Snowdon , (), and an unnamed point, at (), between Langcombe Hill and Shell Top. The best-known tor on Dartmoor is Haytor (called Hey Tor by William Crossing), , (). For a more complete list see List of Dartmoor tors and hills.

Rivers

The high ground of Dartmoor forms the catchment area for many of Devon's rivers. As well as shaping the landscape, these have traditionally provided a source of power for moor industries such as tin mining and quarrying.

The moor takes its name from the River Dart, which starts as the East Dart and West Dart and then becomes a single river at Dartmeet. It leaves the moor at Buckfastleigh, flowing through Totnes below where it opens up into a long ria, reaching the sea at Dartmouth. Other rivers flowing from Dartmoor include the Teign, the Taw, the Tavy, the Avon, and the Lyd.

Some of the rivers in Dartmoor have been dammed to create reservoirs for drinking water, including the River Avon and the South Teign River (Fernworthy Reservoir).

Bogs

Much more rain falls on Dartmoor than in the surrounding lowlands. As much of the national park is covered in thick layers of peat (decaying vegetation), the rain is usually absorbed quickly and distributed slowly, so the moor is rarely dry. In areas where water accumulates, dangerous bogs or mires can result. Some of these, topped with bright green moss, are known to locals as "feather beds" or "quakers", because they can shift (or 'quake') beneath a person's feet. Quakers result from sphagnum moss growing over the water that accumulates in the hollows in the granite.

The vegetation of the bogs depends on the type and location. Blanket bog, which forms on the highest land where the rainfall exceeds a year, consists mainly of cotton-grass (''Eriophorum'' species), sedges (''Carex'' and ''Rhynchospora''), ''Bog Asphodel'' and ''Common Tormentil'', with ''Sphagnum'' thriving in the wettest patches. The valley bogs have lush growth of rushes, with sphagnum, cross-leaved heath, sundews and several other species.

Some of the bogs on Dartmoor have achieved notoriety. Fox Tor Mires was supposedly the inspiration for Great Grimpen Mire in Conan Doyle's novel ''The Hound of the Baskervilles'', although there is a waymarked footpath across it. Sabine Baring-Gould, in his ''Book of Dartmoor'' (1900) related the story of a man who was making his way through Aune Mire at the head of the River Avon when he came upon a top-hat brim down on the surface of the mire. He kicked it, whereupon a voice called out: "What be you a-doin' to my 'at?" The man replied, "Be there now a chap under'n?" "Ees, I reckon," was the reply, "and a hoss under me likewise."

Climate

Along with the rest of South West England, Dartmoor has a temperate climate which is generally wetter and milder than locations at similar height in the rest of England. At Princetown, near the centre of the moor at a height of , January and February are the coldest months with mean minimum temperatures around . July and August are the warmest months with mean daily maxima not reaching . Compared with Teignmouth, which is on the coast about to the east, the average maximum and minimum temperatures are and lower respectively, and frost is at least five times as frequent.Webb 2006, p. 30 On the highest ground, in the north of the moor, the growing season is less than 175 days – this contrasts with some 300 days along most of the south coast of the county.

Rainfall tends to be associated with Atlantic depressions or with convection. In summer, convection caused by solar surface heating sometimes forms shower clouds and a large proportion of rainfall falls from showers and thunderstorms at this time of year. The wettest months are November and December and on the highest parts of the moor the average annual total rainfall is over . This compares with less than in the lower land to the east around the Exe Estuary, which is in the rain shadow of the moor. Due to the influence of the Gulf Stream snowfall is not common, though due to its high altitude it is more vulnerable to snowfall than surrounding regions.Webb 2006, p. 31

Between 1961 and 1990 Met Office data shows that there was an average of 20 days when snow fell on the moor, and over 40 days a year with hail, which is as high as anywhere else in the country. This results when cold polar maritime air that has travelled over a large expanse of warmer ocean is forced to rise over high country.

When average temperatures at Princetown between 1961 and 2000 are compared, the average annual temperature in the decade 1990–2000 was up by and the late winter temperature increased by .Webb 2006, pp. 32–33

Wildlife

Because of Dartmoor's height and granite geology, it experiences strong winds and has acidic soils. In consequence it has been subject to very little intensive farming, and all these factors combine to form the basis of the important ecosystems found here. The landscape is one of granite with peat bogs overlying it. While the moors topped with granite tors are the most iconic part of Dartmoor's landscape, only about half of Dartmoor is actually moorland. Equally important for wildlife are the blanket bogs, upland heaths and the oak woodlands which are all of global importance. Dartmoor is a Special Area of Conservation (SAC) with four habitats (''Northern Atlantic wet heaths with Erica tetralix''; ''European dry heaths''; ''Blanket bog''s and ''Old sessile oak woods with Ilex and Blechnum in the British Isles'') being listed as primary reasons for the selection of Dartmoor as a SAC. In addition the area has a population of the southern damselfly which is also a primary reason for its selection along with populations of Atlantic salmon and otter being qualifying reasons.

Wistman's Wood is one of the old sessile oak woods which contribute to the listing of Dartmoor as a SAC and is possibly a surviving fragment from the earliest Neolithic woodland clearances. It is home to exceptional epiphytic mosses, liverworts and lichens. Nearly 50 species of moss and liverwort are found in the wood along with 120 types of lichen