Geological Forensics 01 EarthCache

This EarthCache demonstrates how Geology and Forensics are often used to together to explain features we find in rocks.

Geology is the study of the Earth; its rocks; its structure; everything within it- and also the processes that shape its surface. Forensics is the use of science and technology to investigate and establish facts. Geologists, and especially palaeontologists, use the evidence found in rocks to deduce the environment that a sedimentary rock or fossil was deposited in, or the 'story' of how the crystals in a metamorphic or igneous rock formed.

The southern section of Portsea Island is below sea level. To help prevent flooding, and to minimise the potential damage caused by waves from the sea, humans have built sea defences along the coast. These defences include groynes, constructing artificial beaches, large convex-sectioned concrete walls, and angled surfaces leading from the promenade down to the sea bed. Some of these angled surfaces have blocks built in to them to disperse the force of the waves, others are simply made of concrete, or are faced with flat rectangular- or square-shaped slabs of natural rock.

The latter have been used as a sea defence on the seaward side of the promenade from the WSW of Southsea Castle, along to the Bluereef Aquarium to the west. The promenade is a 4m wide tarmac path. It has a wall constructed of natural stone on the landward side (BE CAREFUL - the landward side of the wall is a deeper drop than the seaward side). The seaward side of the path is bounded by a 'scaffold' type horizontal barred fence, these supported by uprights at approximately every 1.5m. BE VERY CAREFUL when the sea is either 'high', and/or it is windy, and/or a large ship has just passed by, as waves can easily wash up through this fence, as often shown by the seaweed and flotsam spread along this stretch of the promenade.

Most of the rock slabs on the seaward side of the fence are Purbeck Limestone, quarried from the quarries in nearby Dorset. This Cretaceous-age limestone is itself divided into several distinct sections, each formed in a different environment. One of these is demonstrated here in the slabs used to protect the foreshore - a coastal plain consisting of muddy sands, with shells and evidence of terrestrial 'creatures'.

To Log this EarthCache, please do the following:
Walk westwards along the Promenade from south of Southsea Castle. As the path becomes horizontal, at the seaward side is a slipway (I recommend NOT venturing on this). The horizontal-barred fence then starts. Walk westward along this until you reach the 13th upright. Stand between this and the 14th upright. As usual with EarthCaches there is no physical cache. After looking out to sea to admire the view, look down to where the tarmac, then the concrete, meets the limestone slabs. Study the large western slab, then email the answer to these questions:

1. What are the two 'features' in the rock slab?

2. What 'it' made them?

3. As one looks out to sea, if this rock slab was in its natural location, which way was 'it' moving - to Gosport or Chichester?

Please - no photos of the slabs, as they will give the game away, but please do share photos of yourself and the views :-)