Alum Bay is famous for its coloured sands, chalk Sea Stacks called "The Needles" and lighthouse. It is a designated area of outstanding natural beauty.
It also has fold features, showing both vertical and horizontal rock folds.
The principal routes to the beach are the chair-lift (fee applies) or steps which lead down to the beach from within the 'Needles Park' (clearly signed in the park).
The geology of Alum Bay tells a story of massive biological and physical change spanning 50 million years. The northern and middle sections of the bay are made of Eocene sediments, deposited in a shallow, warm sea between 35-54m years ago whereas the southern end comprises towering chalk cliffs, deposited in deeper water around 80m years ago.
The rocks either side of the chair lift show the different fold features, on the Southern side the strata are vertical whereas those on the Northern side are horizontal.
However, the main reason that Alum is famous is for it's striking coloured sand and cliffs.
The sands are largely derived from the Bracklesham Group, located along the middle sections of the bay. Although the sediments were originally lying horizontally, the pressure of continental movement over millions of years has resulted in localised folding, which is now evident by the vertical position of the beds.
The sands have gained their colour from a variety of sources. Green is provided by glauconite which is common in marine material such as the Barton Clay but is usually much contaminated with clay material. Pure quartz sands can give white. Lignitic material can provide a black colour. Bright yellow might be obtained from jarosite encrustations. Yellow and brownish sands owe their colour to limonite (or goethite) which is the ferric hydroxide (effectively rust). Red colours often indicate early oxidation; this is a process which occurs in palaeosols, ancient soils.
In order to log this cache please go to the posted co-ordinates and: 1. At the posted co-ordinates, find the stronger grey/white vertical rock "wall" which stands proud between yellow/orange and red rock. Estimate the width of this rock and mail the answer to me through my profile above and 2. Ideally take a photo of your GPS with the coloured sands in the background and post this with your log.