Hengistbury Head Geology: Overview

The approach to Hengistbury Head starts approximately 5 metres above sea level, this being just west of the Iron Age defences known as the Double Dykes . About 100 metres East of the Double Dykes the promontory rises steeply and starts to level off at about 30 metres. The head is 36 metres high at its highest point which is approximately a quarter of the way along or about 700 metres from its most easterly point. From this high point Hengistbury Head gently slopes down to a height of approximately 15 metres at its Eastern end. This gently sloping small plateau is known as Warren Hill. Approximately half way along Warren Hill, the Northern aspect of the Hengistbury Head is bisected by a nineteenth century open cast iron ore mine.

As you walk along the beach below Warren Hill, one of the most memorable and distinct features of Hengistbury Head is the clearly defined Strata. The bottom strata dates back about 60 million years. The change in the strata over time illustrate the changing conditions and climate associated with this place. It should be remembered that Hengistbury Head, even with a base 60 million years old is still quite new. No dinosaurs ever walked here, as they had died out many millions of years before the first sands for Hengistbury Head were laid down.

The strata of Hengistbury Head. On the left a new pile of talus (fallen cliff face) waits to be washed into the sea. In timescale from top to bottom is about 60 million years.

During the last Ice age (about 12,000 years ago) Hengistbury Head was several Kilometres inland. At that time the River Stour flowed to the South of Hengistbury Head while the River Avon flowed out to the North. Both of these rivers probably joined into the ancient River Solent that is believed to have meandered through what is now the area of sea between the Isle Of Wight and the mainland, known as the Solent. The Solent River originally flowed into the sea east of Southampton and was contained on its journey by a southerly chalk ridge stretching from the Needles at the Eastern end of the Isle of Wight to Old Harry Rock at Studland. Over time the river eroded into the chalk ridge as at the same time the sea cut into the ridge from the South. Eventually the ridge was breached. The river changed course and initially flowed out to the sea somewhere between the Needles and Old Harry Rock. Further erosion took place and over time the whole ridge was destroyed and the river valley was invaded by the sea.

The River Avon and the River Stour originally took different routes to The River Solent. However eventually they eroded the land separating them and merged into one, near where Christchurch Quay is today. They then followed the path originally taken by the River Avon. The final stretch of the river bed originally used by the River Stour was abandoned.

The old disused Stour river bed where it meets the beach

After the Rivers Stour and Avon merged they followed the same course North of Hengistbury Head. Later on, another small river began to flow in the old Stour bed, but in the opposite direction. It is possible that this river was actually the small River Bourne. Although today this river flows out to sea several kilometres West of Hengistbury Head, in the past, before coastal erosion, the river hooked round and joined the Stour and Avon at Hengistbury Head. Google Earth is part of the free GooglePack S/W and provides excellent zoomable satellite images of Hengistbury Head Note: You need to select the USA version of GooglePack to get Google Earth

The base of the head is formed from Boscombe Sands (a compressed and soft rocklike sand that is easily friable (crumbles)). Above the Boscombe sands is about 3 metres of greenish sandy clay known as the Lower Hengistbury Head Beds. This is topped with up to 15 metres of brown sandy clay. Embedded within this layer are large ( approximately 1-2 metres diameter) boulders of Ironstone. This is known as the Upper Hengistbury Beds. On top of this is about 3 metres of white compressed sand containing islands of clay. This layer is known as the Highcliffe beds. A layer of river bed gravel sits on top of this and is about 1 metre thick. Finally the top of the promontory is covered by a thin topsoil which in the main consists of windblown sand. All of the strata are inclined at about 3 degrees to the horizontal (declining to the south east).

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A rough artists impression of what the Solent River may have looked like 12000 years ago.

Formations similar to those at Hengistbury head can be found further along the coast at Highcliffe and also inland at St Catherine's Mount which is a similar Promontory to Hengistbury Head although it is approximately 3 kilometres inland. St Catherine's Mount, today, probably resembles Hengistbury Head as it was 12,000 years ago.

More detail on strata and other geological aspectsof Hengistbury Head can be found on this link

Geology Part II - The Strata in Detail

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