Steep Holm is one of 2 contrasting islands lying in the middle of the Bristol Channel between Brean Down in Somerset and Barry in South Wales. Rugged Steep Holm is part of Somerset in England whilst nearby low-lying Flat Holm is part of Wales.
Both these locations are formed of carboniferous limestone and are geologically a westwards continuation of the Mendip Hills. The rock was formed in a shallow sea about 300 million years ago from the remains of marine animals - mainly shellfish and corals. Later in geological time, perhaps about 230 million years ago, these rocks were subjected to great movements of the earth's crust which folded them with crests and troughs in an east-west direction – Steep Holm is one of the crests. Red marl from the Triassic period fills some of the joints in the limestone, which shows evidence of karstic (cave forming) processes during this period.
During much of the last 1.8 million years, because so much water was locked up in the Ice Age glaciers, the sea level in the Severn Estuary was some 50 m (160 ft) below the current level and Flat Holm and Steep Holm were joined to the Somerset coast. Sometime since the start of the Mesolithic period, 15,000 years ago, the ice sheets retreated and the flat plains surrounding the river estuary flooded leaving the the highest points as islands in the estuary. Sea levels reached their maximum height around 5,000 BC at which time even Brean Down was a true island.
At present Steep Holm rises 78 metres above sea level and the island is surrounded by steep cliffs as its shoreline is swept by the waters of Bristol Channel, which has one of the highest tidal ranges in the world. This is so great that the island, which covers 63.26 acres (25.6 hectare) at mean low water shrinks to around three quarters of this (48.87 acres) at high tide.
The erosion has produced caves, sea stacks and natural arches, such as the one at the listing co-ordinates at the western end of the island which is known as Rudder Rock.
This will eventually become a sea stack when the rock connection to the island erodes so much that the bridge collapses.
The eastern end of the island is more sheltered from the Atlantic storms but is still swept by fierce currents and these have caused a long spit of pebbles called The Gooseneck to develop out from the East Beach where landing usually occurs.
The island is presently owned by the Kenneth Allsop Memorial Trust, a charity which took over the administration of Steep Holm in 1974 in memory of the broadcaster and naturalist Kenneth Allsop, and purchased it in 1976. The mission statement of the Trust is: "To protect, preserve and enhance for the benefit of the public the landscape, antiquities, flora, fauna, natural beauty and scientific interest of the island of Steep Holm in the County of North Somerset and to advance the education of the public in the natural sciences." The Trust runs day-long boat trips from Weston-super-Mare to a shore landing at East Beach. One of the barrack blocks provides visitor facilities but in order to protect the wildlife, the geology and the public climbing on the cliffs and walking around the base of the island at low tide are prohibited.
To claim this Earthcache you must complete at least 2 of the following 3 tasks (some might be impossible due to the state of the tide or the weather) and (now optional) post photographs of yourself or your gps on the path above Rudder Rock (Danger: Go no further down than N 51 20.385 W 003 06.892 as the cliffs are very steep) and standing with the Gooseneck in the background at low tide (N 51 20.370 W 003 06.248 is a good spot to stand but there are others)
To the best of your ability
1) Estimate the amount of erosion at Rudder Rock as you approach or leave the island. For example do you think that the vertical split is around 80% the height of the cliff, 20% or some other percentage? (The top of the cliff is around 45 metres above sea level by the way)
2) As you land take a photo of the cliff at the head of the beach with its sloping limestone strata. When you upload this onto your computer screen you will be able to measure the angle that the rocks dip at and e mail me this.
3) Walk around the island on the perimeter path and count the number of sea stacks or rocky islets you can see around the coast of the island from this. Make sure you take care and do not stray too close to the crumbling cliff edge and remember that Rudder Rock is not yet a sea stack.
If you e mail me your answers AND post photographs of yourself or your gps at Rudder Rock and The Gooseneck with your log, you can claim this Earthcache.
Note: The Gooseneck is only visible for around an hour at low tide. To work out when you need to be at the photo spot click HERE to find out the times and heights of low and high water on the day of your visit.
Local Archeology & Human Occupation:
Near the beach on Brean Down, where the layers of rock date back to between 14,000 and 10,000 BC, fragments of reindeer, giant deer, Arctic Fox, aurochs, bison, mammoth, wolves and lemmings have been found. These are all animals capable of living in the very cold climate not far away from the ice caps and many were hunted by man. A worked giant deer antler dating to about 10,000 BC has been found in the area and it is probable that Steep Holm saw similar human activity. The island also harbours the remains of a 12th century Augustinian priory.
In the 1800's, following a visit by Queen Victoria and Prince Albert to France where they had been concerned at the strength of the French Navy, both Flat Holm and Steep Holm were fortified to help defend against invasion. The construction of Palmerston Forts on each began in 1865 and was completed in 1869, protecting the approaches to Bristol and Cardiff. Steep Holm had several gun batteries and a central group of brick-built barrack blocks. Some of which are now Scheduled Ancient Monuments.
In WW II, search light batteries were built on Steep Holm, connected to those at the Brean Down Fort by underwater telegraph cable. Parts of the cable were stolen for scrap after the end of WW II, echoes of the past when caves on the western and north-eastern sides of the island were used by smugglers!
The island is now uninhabited with the exception of the wardens, for the island is now protected as a nature reserve, having been made a Site of Special Scientific Interest (SSSI) in 1952. It is also a Geological Conservation Review (GCR) because of the south-western shoreline from the North West Point to Lighthouse Point, where a wave cut portion of the limestone displays large fossil "ripple marks".