Somerset Levels - Geography

Geography

The Levels and Moors are a largely flat area, with the "Moors" referring to the inland plains, and the "Levels" being a coastal sand and clay barrier, roughly west of the M5 motorway. There are some slightly raised parts, called "burtles", as well as higher ridges and hills. The Levels are about 6 metres (20 ft) above mean sea level (O.D.). The general elevation of the inland Moors is 3 to 3.7 metres (10 to 12 ft) O.D. and with peak tides of 7.6 to 7.9 metres (25 to 26 ft) O.D. recorded at Bridgwater and Burnham-on-Sea, respectively, the Moors lie below peak tides. Large areas of peat were laid down in the Moors, particularly in the Brue Valley, during the Quaternary period after the ice sheets melted. The area's topography consists of two basins mainly surrounded by hills, the runoff from which forms rivers that originally meandered across the plain but have now been controlled by embanking and clyses (the local name for a sluice). The area is prone to winter floods of fresh water and occasional salt water inundations. The worst in recorded history was the Bristol Channel floods of 1607, which resulted in the drowning of an estimated 2,000 or more people, houses and villages swept away, an estimated 200 square miles (518 km2) of farmland inundated, and livestock destroyed. Another severe flood occurred in 1872–1873, when over 107 square miles (277 km2) were underwater from October to March.

Although underlain by much older Triassic age formations that protrude to form what would once have been islands—such as Athelney, Brent Knoll, Burrow Mump and Glastonbury Tor—the lowland landscape was formed only during the last 10,000 years, following the end of the last ice age. Glastonbury Tor is composed of Upper Lias Sand. The Poldens and the Isle of Wedmore are composed of Blue Lias and Marl, while the Mendips are largely Carboniferous limestone. Although sea level changes since the Pliocene led to changes in sea level and the laying down of vegetation, the peak of the peat formation took place in swamp conditions around 6,000 years ago, although in some areas it continued into medieval times.

It is a mainly agricultural region, typically with open fields of permanent grass surrounded by ditches with willow trees. Access to individual areas of the Moors and Levels, especially for cattle, was provided by means of "droves", i.e. green lanes, leading off the public highways. Some of the old roads, in contrast to the old hollow ways found in other areas of England, are causeways raised above the level of the surrounding land, with a drainage ditch running along each side.