2 Million years display!
The Hilbre Islands consist of a ridge of Bunter sandstone of the lower Triassic period ( 180 million -225 million years old). This was an area of dry climate ,but sudden, heavy rainfalls caused periods of flooding in the desert.
Sandstone is the main rock type on Hilbre. Pebble layers (conglomerates) can be found in parts of the island and are the result of material that has been moved a short distance as a result of river flash floods.
Mudstones are also present on the island. These were left behind at the end of a period of flooding. It is in these beds that tracks of dinosaurs ,such as the Pseuduchium Archosaurs have been found. These creatures are thought to have roamed the muddy desert surface leaving their footprints behind.
The rocks were affected by later earth movements and the rock layers were tilted by 10 degrees towards the north east. These were later cracked and faulted by subsequent earth movements.
Hilbre Island is disappearing...
The topography of the Hilbre Islands can be attributed to a combination of the underlying geology of the area and the effects of the continuous erosion of the sea over a period of several thousand years. The islands themselves consist of a low plateau with a maximum height of 56 feet above mean sea level on the west side.
The islands are constantly being undercut by the sea. Evidence of cliff fall can be seen be seen in a number of places as well as well as other geomorphological features such as caves (Lady’s Cave),stacks(Lion Rock),wave cut platforms and small sandy beaches( Niffy Bay).
The islands are known from historical records to have reduced considerably in size in the last 2000 years due to the erosion by the sea despite efforts in Victorian times to build extensive retaining walls on the west side of the island. Little Eye is now almost completely eroded and further coastal defences are needed to stop further erosion of this unique island group.