An Apostle - A Limestone Stack - Explored!
A stack or sea stack is a geological landform consisting of a steep and often vertical column or columns of rock in the sea near a coast, formed by wave erosion. Stacks typically form in horizontally-bedded sedimentary or volcanic rocks (clearly seen above on what is probably a 25-30m-high stack), particularly on limestone cliffs. Stacks are formed over time by wind and water, processes of coastal geomorphology.
They are formed when part of a headland is eroded by hydraulic action, which is the force of the sea or water crashing against the rock. The force of the water weakens cracks in the headland, causing them to later collapse, forming free-standing stacks and even a small island. Without the constant presence of water, stacks also form when a natural arch collapses under gravity, due to sub-aerial processes like wind erosion. Erosion causes the arch to collapse, leaving the pillar of hard rock standing away from the coast - the stack. Eventually, erosion will cause the stack to collapse, leaving a stump. Stacks can provide important nesting locations for seabirds, and many are popular for rock climbing.
The stack above is one of the world-famous Twelve Apostles in Port Campbell National Park, seen in early morning sunshine. The Twelve Apostles are a collection of limestone stacks by the Great Ocean Road in Victoria, Australia. Their proximity to one another has made the site a popular tourist attraction - although I was the only person around at this time of day!
An Apostle - A Limestone Stack - Explored!
A stack or sea stack is a geological landform consisting of a steep and often vertical column or columns of rock in the sea near a coast, formed by wave erosion. Stacks typically form in horizontally-bedded sedimentary or volcanic rocks (clearly seen above on what is probably a 25-30m-high stack), particularly on limestone cliffs. Stacks are formed over time by wind and water, processes of coastal geomorphology.
They are formed when part of a headland is eroded by hydraulic action, which is the force of the sea or water crashing against the rock. The force of the water weakens cracks in the headland, causing them to later collapse, forming free-standing stacks and even a small island. Without the constant presence of water, stacks also form when a natural arch collapses under gravity, due to sub-aerial processes like wind erosion. Erosion causes the arch to collapse, leaving the pillar of hard rock standing away from the coast - the stack. Eventually, erosion will cause the stack to collapse, leaving a stump. Stacks can provide important nesting locations for seabirds, and many are popular for rock climbing.
The stack above is one of the world-famous Twelve Apostles in Port Campbell National Park, seen in early morning sunshine. The Twelve Apostles are a collection of limestone stacks by the Great Ocean Road in Victoria, Australia. Their proximity to one another has made the site a popular tourist attraction - although I was the only person around at this time of day!