Kent
Kent is a county in southeast England.
Kent is at the southeastern end of England. It borders the River Thames and the North Sea to the north, and the Straits of Dover and the English Channel to the south. France is 21 miles (34 km) across the Strait.
The major geographical features of the county are determined by a series of ridges and valleys running east-west across the county. These are the results of weathering to the Wealden dome, a dome across Kent and Sussex created by Alpine movements 10 20 million years ago. This dome consists of an upper layer of chalk above subsequent layers of upper greensand, upper clay, lower greensand, lower clay, and red sandstone. The ridges and valleys formed as the exposed clay eroded faster than the exposed chalk, greensand, or red sandstone.
Geological map of southeast England, showing a concentric circular pattern formed by the weathering of the Wealden dome.Sevenoaks, Maidstone, Ashford, and Folkestone are built on greensand, while Tonbridge and Tunbridge Wells are built on red sandstone. Dartford, Gravesend, the Medway towns, Sittingbourne, Faversham, Canterbury, Deal, and Dover are built on chalk. The easterly section of the Wealden dome has been eroded away by the sea, and cliffs such as the white cliffs of Dover are present where a chalk ridge known as the North Downs meets the coast. Spanning Dover and Westerham is the Kent Downs Area of Outstanding Natural Beauty.
The Wealden dome is a Mesozoic structure lying on a Palaeozoic foundation, which usually creates the right conditions for coal formation. This is found in East Kent roughly between Deal, Canterbury, and Dover. The coal measures within the Westphalian Sandstone are deep (below 244 m 396 m) and subject to flooding. They occur in two major troughs, which extend under the English Channel where similar coalfields are located.
Seismic activity has occasionally been recorded in Kent, though the epicentres were offshore. In 1382 and 1580 there were two earthquakes exceeding 6.0 on the Richter Scale. In 1776, 1950, and on 28 April 2007 there were earthquakes of around 4.3. The 2007 earthquake caused physical damage in Folkestone.
Geological cross section of Kent, showing how it relates to major townsThe coastline of Kent is continuously changing, due to tectonic uplift and coastal erosion. Until about 960, the Isle of Thanet was an island, separated by the Wantsum channel, formed around a deposit of chalk; over time, the channels silted up with alluvium. Similarly Romney Marsh and Dungeness have been formed by accumulation of alluvium.
Kent's principal river, the River Medway, rises near East Grinstead in Sussex and flows eastwards to a point near Maidstone. Here it turns north and breaks through the North Downs at Rochester, then joins the River Thames as its final tributary near Sheerness. The Medway is some 70 miles (113 km) long. The river is tidal as far as Allington lock, but in earlier times, cargo-carrying vessels reached as far upstream as Tonbridge. The Medway has captured the head waters of other rivers such as the River Darent. Other rivers of Kent include the River Stour in the east.